MMOSAl. KfnmHat^ U.S. DEPARTMENT OF COMMERCE Elliot L. Richardson, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator ENVIRONMENTAL RESEARCH LABORATORIES Wilmot N. Hess, Director Collected Reprints-1974 Volume II ATLANTIC OCEANOGRAPHIC AND METEOROLOGICAL LABORATORIES ISSUED SEPTEMBER 1976 Boulder, Colorado a a u o a a a 3* Atlantic Oceanographic and Meteorological Laboratories Miami, Florida 33149 For sale by the Superintendent of Documents, U. S. Government Printing.OHice, Washington, D. C. 20402 FOREWORD This is the ninth annual publication of collected reprints which brings together the published research results of the NOAA Atlantic Oceanographic and Meteorological Laboratories (AOML). This publication provides a single source for articles which ap- peared in various scientific journals, and those which appeared as internal scientific and technical publications, during 1974. The Atlantic Oceanographic and Meteorological Laboratories conduct research programs to study the physical, chemical, and geological characteristics and processes of the ocean waters, the sea floor, and the atmosphere above the ocean. During 1974, these programs were organized among the Director's office and four major groups: Ocean Remote Sensing Laboratory Physical Oceanography Laboratory Marine Geology and Geophysics Laboratory Sea-Air Interaction Laboratory The reprints in this collection are arranged alphabetically by first author within each of these groups. Harris B. Stewart, Jr. Atlantic Oceanographic and Meteorolog- Di rector, AOML ical Laboratories NOAA/Environmental Research Laboratories 15 Rickenbacker Causeway Virginia Key Miami, Florida 33149 U.S.A. m Digitized by the Internet Archive in 2012 with funding from LYRASIS Members and Sloan Foundation http://archive.org/details/collectedreprintOOatla CONTENTS VOLUME I General 1. Stewart, Harris B., Jr. A New Look at the CHALLENGER Expedition, International Oceanographic Foundation Publication, Sea Frontiers 20, No. 6, 333-337, Nov. -Dec. 1974. 1 2. Stewart, Harris B., Jr. Current from the Current, Oceanus 17, (Woods Hole Oceanographic Institution), 38-41, Summer 1974. 6 3. Stewart, Harris B., Jr. The Sea and Its Resources (El Mar Y Sus Recursos), Science 183, 224, Jan. 1974. 10 4. Stewart, H. B., Jr. Federal Agency Activities in Marine Science Assistance to Developing Countries, Conf. Proc. U. S. Marine Scientific Research Assistance to Foreign States (National Academy of Sciences), 13-15, Mar. 1974. 11 5. Stewart, H. B. , Jr. NOAA's Activities in Marine Science Assistance to the Developing Countries, Conf. Proc. U. S. Marine Scientific Research Assistance to Foreign States (National Academy of Sciences), 202-211, Mar. 1974. 15 6. Stewart, H. B. , Jr. The Bologna Workshop on Marine Science, Conf. Proc U. S. Marine Scientific Research Assistance to Foreign States (National Academy of Sciences), 241-247, Mar. 1974. 25 7. Von Arx, W. S., H. B. Stewart, Jr., and J. R. Apel The Florida Current as a Potential Source of Useable Energy, MacArthur Workshop on Energy from the Florida Current, Palm Beach Shores, Florida, 91-103, Feb. 27- Mar. 1, 1974. 32 Ocean Remote Sensing 8. Apel, J. R. Statement on Seasat-A; Hearings before the Subcommittee on Space Science and Applications, Committee on Science and Astronautics, U. S. House of Representatives, No. 25, Part 3, 270-290, U. S. Government Printing Office (identical testimony given before the Senate), Feb. -Mar. 1974. 44 9. Apel, J. R., and H. M. Byrne Oceanography and the Marine Geoid; Proc. Inter. Symposium on Applications of Marine Geodesy, Marine Technology Society, Washington, D. C, 59-66, 1974. 65 10. Apel, J. R., and R. L. Charnell Ocean Internal Waves off the North American and African Coasts From ERTS-1; Proc. 3rd ERTS-1 Symposium, I3 Section B, NASA SP-351, Paper M2, Goddard Space Flight Center, 1309-1316, 1974. 73 11. Apel, J. R., R. L. Charnell, and R. J. Blackwell Ocean Internal Waves off the North American and African Coasts From ERTS-1; Proc. 9th Inter. Symposium on Remote Sensing of the Environment II, Ann Arbor, Michigan, 1345-1351, 1974. 81 12. Apel, J. R., and J. R. Proni Scientific Results From Remote Sensing of the Oceans; Marine Technology Society Journal 8, 25-28, Jan. 1974. 88 13. Apel , J. R., and J. W. Siry A Synopsis of Seasat-A Scientific Contributions, Sect. 1 of Seasat-A Scientific Contributions, National Aeronautics and Space Admin., Special Report to the National Science Founda- tion, 3-13, 1974. 93 14. Apel , J. R., and J. W. Siry The Earth and Ocean Physics Applications Program (EOPAP): Ocean Dynamics Program, Sect. 3 of Seasat-A Scientific Contributions, National Aeronautics and Space Admin., Special Report to the National Science Foundation, 139-151, 1974. 104 VI 15. Byrne, H. M., and W. 0. von Arx Geostrophic Current Investigations with Seasat, Seasat-A Scientific Contributions, National Aeronautics and Space Admin., Special Report to the National Science Foundation, 41-44, 1974. 117 Physical Oceanography 16. Charnell, R. L., J. R. Apel , W. Manning, III and R. H. Qualset Utility of ERTS-1 for Coastal Ocean Observation: The New York Bight Example, Marine Technology Soeiety Journal 8, No. 3, 42-47, Mar. 1974. 121 17. Charnell, R. L., and D. V. Hansen Summary and Analysis of Physical Oceanography Data Collected in the New York Bight Apex During 1969-70, NOM-MESA Report No. 74-33 44 pages, Aug. 1974. 127 18. Chew, F. The Turning Process in Meandering Currents: A Case Study, Journal of Physical Oceanography 4, No. 1, 27-57, Jan. 1974. 174 19. Dietz, R. S. Book Review. A Revolution in the Earth Sciences: From Continental Drift to Plate Tectonics (A. Hal lam. Clarendon, Oxford 1973), American Geophysical Union EOS 55, No. 4, 181-182, Apr. 1974. 205 20. Hansen, D. V. Book Review. Estuaries: A Physical Introduction, (K.R. Dyer. Wiley, Chichester, 1973) Marine Geoloqy 16, 161-162, 1974. 207 21. Hansen, D. V. Book Review. Marine Physics, (R.E. Craig. Academic Press, New York, 1972) American Meteorological Society 55 3 No. 10, 1244, Oct. 1974. 209 22. Hansen, D. V., and J. F. Festa Inlet Circulation Induced by Mixing of Stratified Water Masses, Rapp. R. -v. Reun. Cons. Int. Explor. Mer. 167, 163-170, Dec. 1974. - 210 vn 23* Hazelworth, J. B., B. L. Kolitz, R. B. Starr, R. L. Charnell and G. A. Berberian New York Bight Project, Water Column Sampling Cruises #1-5 of the NOAA Ship FERREL, August-November 1973, NOM-MESA Report, No. 74-2, 191 Pages, July 1974. 218 24. Herman, A. Atlantic Oceanographic and Meteorological Laboratories Com- puter Users Guide, NOAA Technical Memorandum ERL AOML-25, 89 pages, Nov. 1974. 412 25. Maul, G. A. Applications of ERTS Data to Oceanography and the Marine Environment, COSPAR Approaches to Earth Survey Problems Through Use of Space Techniques, Proceedings of the Sympo- sium held in Constance, F.R.G., 335-347, May 23-25, 1973. 506 26. Maul, G. A. The Gulf Loop Current, Proceedings of Conference/Workshops on Marine Environmental Implications of Offshore Drilling Eastern Gulf of Mexico , 87-96, Jan. 31, Feb. 1-2, 1974. ' 520 27. Maul, G. A. Relationships Between ERTS Radiances and Gradients Across Oceanic Fronts, Third Earth Resources Technology Satellite - 1 Symposium, Vol. 13 Paper Ml, Technical Presentations Section B, National Aeronautics and Space Administration, 1279-1308, Dec. 1973. 531 28. Maul, G. A. Remote Sensing of Ocean Currents Using ERTS Imagery, Revue Photo-Interpretation, 50-65, 1973-4. 561 29. Maul, G. A., R. L. Charnell, and R. H. Qualset Computer Enhancement of ERTS-1 Images for Ocean Radiances, Remote Sensing of Environment 3, 237-252, 1974. 577 30. Maul, G. A., D. R. Norris, W. R. Johnson Satellite Photography of Eddies in the Gulf Loop Current, Geophysical Research Letters 1, No. 6, 256-258, Oct. 1974. 594 vm 31. Mofjeld, H. Book Review. "Estuaries: A Physical Introduction", Limnology and Oceanography 18, No. 6, 1012, Nov. 1973. 597 32. Mofjeld, H. 0. Tidal Currents on the West Florida Shelf, Proceedings of Conference /Workshops on Marine Environmental Implica- tions of Offshore Drilling Eastern Gulf of Mexico, 127-130, Jan. 31, Feb. 1-2, 1974. 598 33. Molinari, R. L Data From the NOAA Ship VIRGINIA KEY and the SUSIO Ship BELLOWS, Collected During CICAR Survey Month II, NOAA Technical Memorandum ERL AOML-22 , 153 pages, Aug. 1974. 603 34. Segar, D. A. Flameless Atomic Absorption Gas Chromatography, Analytical Letters 7, No. 1, 89-95, Jan. 1974. 759 35. Whitehead, J. A., A. Leetmaa, and R. A. Knox Rotating Hydraulics of Strait and Sill Flows, Geophysical Fluid Dynamics 6, 101-125, 1974. 766 VOLUME II Marine Geology and Geophysics 36. Dietz, R. S. Ocean Basins, Encyclopedia Britannica 13, 15th Edition, Macropedia, 433-437, 1974. 791 37. Dietz, R. S The Oceans From Sky lab 4, Sea Frontiers 20, No. 6, 359-363, Nov. -Dec. 1974. 796 38. Dietz, R. S, Ocean Wide, Ocean Deep, Industrial Research 16, No. 12, 58-63, Nov. 1974. 801 IX 39. Dietz, R. S., and J. C. Holden Collapsing Continental Rises: Actual is tic Concept of Geo- synclines - A Review, Modern and Ancient Geosynclinal Sedi- mentation, eds., R. H. Dott, Jr. and R. H. Shaver, Society of Economic Paleontologists and Mineralogists Spec. Pub I. No. 19, 14-25, 1974. 807 40. Dietz, R. S., and J. McHone Impact Structures From ERTS Imagery, Meteoritics 93 No. 4, 329-334, 1974. 820 41. Dorman, L. M., and J. W. Lavelle A Connected Least-Squares Adjustment of Navigation Data, NOAA Technical Report ERL 303-AOML 153 54 pages, July 1974. 826 42. Dorman, L. M. , and B. T. R. Lewis The Use of Nonlinear Functional Expansions in Calculation of the Terrain Effect in Airborne and Marine Gravimetry and Gradiometry, Geophysics 39, No. 1, 33-38, Feb. 1974. 883 43. Drake, David E. Suspended Particulate Matter in the New York Bight Apex: September - November 1973, NOAA Tech Report ERL 318-MESA l3 53 pages, Nov. 1974. 889 44. Drake, D. E., D. A. Segar, R. L. Charnell, and G. A. Maul Comparison of Optical Measurements and Suspended Solids Concentrations in the Ocean, Proceedings NOIC Turbidity Workshop, Washington, D. C, 123-141, May 1974. 945 45. Keller. G. H. Marine Geotechnical Properties: Interrelationships, and Relationships to Depth of Burial, Veep Sea Sediments, 77-100, 1974. 964 46. Keller, G. H. Mass Physical Properties of Some Western Black Sea Sedi- ments. The Black Sea: Geology, Chemistry and Biology, eds. E. T. Degens D. A. Ross, AAPG Memoir 20 3 332-337, 1974. 988 47. Lattimore, R. K., P. A. Rona, and 0. E. DeWald Magnetic Anomaly Sequence in the Central North Atlantic, Journal of Geophysical Research 79, No. 8, 1207-1209, Mar. 1974. 995 48. McKinney, T. F., W. L. Stubblefield, and D. J. P. Swift Large-Scale Current Lineations on the Central New Jersey Shelf: Investigations By Side-Scan Sonar, Marine Geology 17, 79-102, 1974. 998 49. Nelsen, T. A. An Automated Rapid Sediment Analyzer (ARSA) , NOAA Technical Memorandum EEL AOML-21, 26 pages, May 1974. 1022 50. Peter, G., C. Schubert, and G. Westbrook Caribbean Atlantic Geotraverse, Geotimes, 12-15, Aug. 1974. 1051 51. Rona, P. A. Relation in Time Between Eustacy and Orogency: A Presently Indeterminate Problem, Geology 2, No. 4, 201-202, April 1974. 1055 52. Rona, P. A. Subsidence of Atlantic Continental Margins, Tectonophysics 22, 283-299, 1974. 1056 53. Rona, P. A., and R. S. Dietz Sediment Accumulation, Sea-Floor Spreading5and Eustacy: Reply, Geological Society of America Bulletin 85, 831-832, May 1974. 1073 54. Rona, P. A., R. N. Harbison, and S. A. Bush Abyssal Hills of the Eastern Central North Atlantic, Marine Geology 16, 275-292, June 1974. 1074 55. Rona, P. A., and D. U. Wise Symposium: Global Sea Level and Plate Tectonics Through Time, Geology 2, No. 3, 133-4, 1974. 1092 XT 56. Rowe, G. T., G. Keller, H. Edgerton, N. Stares inic, and J. Macllvaine Time-Lapse Photography of the Biological Reworking of Sediments in Hudson Submarine Canyon, Journal of Sedimentary Petrology 44, No. 2, 549-552, June 1974. 1094 57. Scott, M. R., R. B. Scott, P. A. Rona, L. W. Butler, and A. J. Nalwalk Rapidly Accumulating Manganese Deposits from the Median Valley of the Mid-Atlantic Ridge, Geophysical Research Letters 1, No. 8, 355-358, Dec. 1974. 1098 58. Scott, R. B., P. A. Rona, B. A. McGregor, and M. R. Scott The TAG Hydrothermal Field, Nature 251, No. 5473, 301-302, Sept. 1974. 1102 59. Stubblefield, W. L., M. Dicken, and D. J. P. Swift Reconnaissance of Bottom Sediments on the Inner and Central New Jersey Shelf (MESA Data Report), MESA Report No. 1, 39 pages, July 1974. 1104 60 Swift, D. J. P. Continental Shelf Sedimentation, Geology of Continental Margins: a survey volume, 117-135, 1974. 1145 61. Swift, D. J. P., and P. Sears Estuarine and Littoral Deoisitional Patterns in the Surficial Sand Sheet Central and Southern Atlantic Shelf of North America, Memoires de V Institut de Geologie du Bassin D'Aquitaine 7, 171-189, 1974. 1164 Sea-Air Interaction 62. Au, B., J. Kenney, L. U. Martin, and D. Ross Multi -Frequency Radiometric Measurements of Foam and a Mono-Molecular Slick, Proceedings of the Ninth Inter- national Symposium on Remote Sensing of Environment } Vol. Ill, Willow Run Laboratories, Ann Arbor, Michigan, 1763-1773, Apr. 15-20, 1974. 1183 xn 63. Augstein, E., H. Schmidt, and F. Ostapoff The Vertical Structure of the Atmospheric Planetary Bound- ary Layer in Undisturbed Trade Winds Over the Atlantic Ocean, Boundary -Layer Meteorology 6, 129-150, 1974. 1194 64. Cram, R., and K. Hanson The Detection by ERTS-1 of Wind-Induced Ocean Surface Features in the Lee of the Antilles Islands, Journal of Physical Oceanography 4, No. 4, 594-600, Oct. 1974. 1216 65. Hanson, K. J. Comments on the Quality of the NWS Pyranometer Network Data from 1954 to the Present, Report and Recommendations of the Solar Energy Data Workshop, Nov. 29-30, 1973, National Science Foundation NSF-RA-N-74-062, 31-33, Sept. 1974. 1223 66. Hanson, K. J. Radiation Sensor Comparisons During the GATE International Sea Trails (GIST), Bulletin American Meteorological Society 553 No. 4, 297-304, Apr. iy/4 (also published with data as N0AA Technical Report ERL 301-A0ML 14, Apr. 1974). 1226 67. Hanson, K. (Editor), E. Flowers, G. Herbert, D. Hoyt, P. Kuhn, S. Manabe, R. Pueschel , and L. Stearns Environmental Research Laboratories Radiation Programs - Requirements and Recommendations, NOAA Technical Report ERL 300-OD 12 3 22 pages, May 1974. 1268 68. Lamb, D. , and W. D. Scott The Mechanism of Ice Crystal Growth and Habit Formation, Journal of Atmospheric Sciences SI, No. 2, 570-580 Mar. 1974. 1292 69. Ostapoff, F., and S. Worthem The Intradiurnal Temperature Variation in the Upper Ocean Layer, Journal of Physical Oceanography 4, No. 4, 601-612, Oct. 1974. ' 1303 xi n 70. Ross, D., B. Au, W. Brown, and J. McFadden A Remote Sensing Study of Pacific Hurricane AVA, Pro- ceedings of the Ninth International Symposium on Remote Sensing of Environment 1, Willow Run Labora- tories, Ann Arbor, Michigan, 163-180, Apr. 15-19, 1974. 1315 71. Ross, D. B., and V. Cardone Observations of Oceanic Whitecaps and Their Relation to Remote Measurements of Surface Wind Speed, Journal of Geophysical Research 79, No. 3, 444-452, Jan. 1974. ' 1333 72. Scott, W. D., and Z. Levin Reply to "Comments on the Effect of Potential Gradient on the Charge Separation During Interactions of Snow Crystals with an Ice Sphere", Journal of Atmospheric Sciences 31, No. 2, 598-599, Mar. 1974. 1342 73. Webster, W. J., Jr., T. T. Wilheit, D. B. Ross, and P. Gloersen Analysis of the Convair-990 Passive Microwave Observations of the Sea States During the Bering Sea Experiment, Results of the U.S. Contribution to the Joint U.S./U.S.S.R. Bering Sea Experiment, Goddard Space Flight Center, Greenbelt, Maryland, 165-193, May 1974 (Also published in Proceedings of the Symposium on the Analysis of Data Collected on Joint U.S.-U.S.S.R. Bering Sea Experiment, Leningrad, U.S.S.R., May 1974). 1344 xiv Ocean Basins 433 Explora- tion and develop- ment Dietz, R„S. (1974) Ocean Basins, Encycl. Britannica, 15th Ed. v. 13, Kacropedia, p. 433-438. Ocean Basins The ocean basins and the continents constitute the largest relief features on ^liarth, with the ocean basins, covering three-fifths of the Earth's surface, dominant. Water, in- cluding that of the shallow seas, actually covers 71 per- cent of the Earth, but only 60 percent of this overlies the deep ocean basins, which occur below the 2,000-metre (6,500-foot) contour line. The average depth of the sea is 3,800 metres (12.500 feet), whereas the average height of the continents is 840 metres (2,760 feet). Thus, the total relief contrast is 4,640 metres (15,220 feet). The distribution of ocean basins and continents is asym- metrical. Continents are generally antipodal (diametri- cally opposed) to ocean basins. The antipodal position of Australia, for example, is within the North Atlantic Ba- sin, and Antarctica opposes the Arctic Basin. The ocean basins lie principally in the Southern Hemisphere, and the Antarctic Basin encircles the Earth. In a sense, ihe three major oceanic basins (Pacific, Atlantic, and Indian) may be regarded as huge gulfs that extend off the Antarc- tic Basin, wiih the Arctic Basin being a secondary north- ward extension of the Atlantic. Thus, unlike the separated and isolated continents, the ocean basins are all intercon- nected, so that there is really only one worldwide ocean basin. This ocean basin is subdivided into a number of individual ocean basins largely as a matter of conve- nience. A classical view of natural philosophers held the oceans to be as deep as the mountains arc high, which is roughly correct if only the greatest mountains aie considered. The first deep-sea sounding was made in the centra! South Atlantic in 1840; a heavy plummet was lowered 2,425 fathoms (4,435 metres 114.500 feet)) on the end of a long line. The first generalized map of the ocean basins was fashioned in 1895, using the 7,000 oceanic soundings deeper than 2,000 metres (6,500 feet) that were then available. The advent of the echo sounder in 1920, with which precisely timed echoes are bounced off the bottom, revolutionized deep-sea soundings. A modern survey ship can obtain a sounding every second along its track. The problem of obtaining accurate position control, or fi\es, under all conditions of weather and in any part of the world was solved recently through satellite navigation, determination of fixes continuously from low-orbited satellites. The bathymetry (depth measurement) of the entire ocean floor is rapidly being revealed and charted in the 1970s with literally millions of soundings. Before about 1930 the ocean floor was regarded as flat, monotonous, and generally featureless. Charts since then show a topography remarkably varied in both shape and relief. Some seamounts (isolated conical submarine peaks) and escarpments (steep slopes) are higher and more rugged than any on land, whereas the abyssal (deep-sea) plains aie the levelest surfaces on the face of the globe. It has also been learned that the ocean floor, like the surface of the Moon, is a distinct geomorphic domain {i.e., occupied by distinctive landforms); con- structional and depositional physiography are quite un- like that on land. Erosional landforms on the continents are iculptured by wind, ice, and running water, but only sluggishly moving water modifies the deep ocean floor. Terrestrial stream action is imitated beneath the sea by turbidity currents, mud-laden tongues of water that peri- odically pour down the continental shelves and slopes to the ocean floor. Weathering (rock disintegration by chemical and mechanical processes), as weil as erosion, proceeds slowly beneath the sea, so that the sea-floor morphology (fault scarps, volcanic knolls, and other fea- tures) tends to retain a pristine appearance. Undersea constructional topography commonly differs from that on land. There is, for example, no undersea equivalent of folded sedimentary mountains. The major features of the ocean floor are deep-sea trenches, rifts, and fracture zones that are created by the interaction along their boundaries of shifting rigid crustal plates. The giant volcanic cones that create seamounts are especially spectacular. The smaller features represent a variety of volcanic topographic forms, related mainly to fissure eruptions (along linear cracks rather than through a cen- tral vent) and rifting of the ocean floor. The mineral-resource potential of the deep ocean floor commonly has been considerably overstated. Basalt, which is the common rock of the oceanic crust and of seamounts, offers uninteresting mineral prospects. Ice- land and Hawaii provide subaerial examples of oceanic rocks, and these, like all oceanic islands, have little to offer in the way of useful minerals. On the other hand, much interest has been accorded to marine phosphorites and manganese nodules, both of which are formed on the sea floor. The manganese nodules may someday be com- mercially recovered because of their high content of cop- per, nickel, and cobalt. Metalliferous sediments beneath pockets of hot brine in the Red Sea are another possibili- ty. Also a highly mineralized layer commonly lies be- tween the sediments on the sea floor and the underlying oceanic crust. With tne exception of precious coral, there is no mining of the deep-sea floor today. Precious coral occurs primar- ily around some of the coral atolls and seamounts of the central western Pacific, where it is gathered from deep crevices by the Japanese. This article treats the geologic and geographic features of the ocean basins and includes a section on their origin. For further information on the areas marginal to ocean basins, see continental shf.lf and slope, and for treatment of sediment transport from these areas to the ocean basins see canyons, submarine; density cur- rents. See also oceans and seas; oceanic ridges; and gea-floor SPREADING for additional detail on oceanic pro- cesses of relevance and earth, physiography of for an overview of the dimensions and interrelations of land and sea areas. COMPONENTS OF OCEAN BASINS The oceanic crust. The oceanic crust contrasts sharply with ihe granitic crust that makes up the continental blocks. The ocean floor is separated from the Earth's upper mantle (zone beneath the crust) by three distinct layers, which have been revealed by seismic refraction studies. These are: Layer 1 (zero-two kilometres [zero-one mile] thick), consisting of unconsolidated sed- iments that have been derived from the continents by submarine density currents or surface transport; Layer 2, Mineral resources 791 434 Ocean Basins v \T SV* ^-J i ! / !'• - • \ ' v. ^^ S-ia™ • .. ■ •> **^~ Azores Plateau vV- V^. ,>> f *s v\ A. . v •- — llC^iS^*,' ■•"•■' -.•■>>-. ." '•■- ^ .-Ampere • , \ / vV, r^ «-•■!►' •" >')Un '*n'Jl- ' V- i '..V->' Madeira -N '' - t#-s f ' r, .C? ' Bermuda islands J^. . V / • \V VfcolrSeamounl Plato Searhourrts ^T * I \ \* -• --P •• » ■ . ..-•." i -..- V.W '/ •• «."v - • ' r v Canary ,, ' -'/I ^- \ i ! Wr >f ^ < ■ ■■ . v ■ ■ '*,a^ v J y •:.v.v- •-. ^ ., . ■ ". •-.> "-_v,r.. ■ 'v^n* :■>:>.'. ■-:,'•■> v; // ..'»•„■ ^. V - '^U, - . w ♦"■" ■■■'^'•U, ' '•',1V''V'>i''A.1 Kryiov Cape Verde -M^. Midoceanic ridge, fracture zones, and sea-floor topography of the North Atlantic. Drawing by E. Derdeyn Relation of rocks and features to plate tectonics comprising Layer 2a (0.5 kilometre [0.3 mile] thick), consisting of pillow lava, a submarine form produced by the rapid quenching of lava as it poured from fissures onto the ocean floor, and Layer 2b (two kilometres [one mile] thick), a series of feeder dikes (dikes are solidified sheets of lava that intrude pre-existing rocks) that origi- nally provided passages for the lavas onto the ocean floor; and Layer 3 (five kilometres [three miles] thick), consisting principally of gabbro, a coarse, crystalline, basic intrusic rock, a form of olivine basalt. Unlike the sediments that arc added by deposition from above, these igneous rocks are all injected from below. They are de- rived by the partial melting of the primitive iron- and magnesium-rich rock of the upper mantle. The nature of the igneous crustal layers found below the sediments is in accord with the concept of sea-floor spreading (q. v.). As 100-kilometrc- (60-mile-) thick litho- spheric plates move apart at midocean rifts, mantle rock moves up from below to fill the void. Much of this injec- tion takes place by viscous-solid flow, but there is also some molten rock present that is squeezed to the top. Outpouring of lava onto the sea floor is quickly chilled into bolster-shaped pods with glassy surfaces that are called pillow lavas (Layer 2). Beneath these pillow lavas are feeder dikes, along which the lava rose to the sea floor. With sea-floor spreading these dikes are pulled apart and injected with new dikes, forming a complex system of dikes (Layer 2b). These dikes are derived from an underlying layer of magma that cools slowly and crys- tallizes to form gabbro (the intrusive equivalent of ol- ivine basalt) and associated suites of rocks. This interpretation of the oceanic crust is not fully agreed upon by all authorities. According to this interpre- tation, however, all of the oceanic crustal rocks have the general composition of olivine basalt. Major features. The major features within the ocean basins arc the midocean ridges (rises), trenches, and frac- ture zones. These grand features arc related, because they are all associated with the boundaries of the Earth's ma- jor crustal plates. These boundaries almost invariably lie within the ocean basins rather than on the continents. The trenches mark zones of undcrthmsting associated with the descent of the crust into the mantle; the mid- ocean ridge forms along the pull-apart zones; and the fracture zones reflect lines of crustal disruption associated with great shearing action where one crustal plate has slid past its neighbour. Thus, the concept of plate tec- tonics (that the Earth's surface consists of a small number of crustal plates the boundaries of which are sites of ma- jor deformation) accounts for these three major types of features that dominate the ocean basins. Midocean ridges. The midocean-ridge system actually forms a continuous swell throughout the world oceans with an overall length of 60,000 kilometres (37,000 miles), or more than the circumference of the Earth. It is a broad arch one to three kilometres high which may be either exceedingly rough or quite smooth. It is by far the largest and most extensive mountain range on the face of the Earth. Nearly everywhere it is deeply submerged, with only an occasional small island, such as Saint Helena or Ascension, narking its presence. Iceland alone is an exposed broad expanse of the spine of a midocean ridge. The expansion of rocks when hot apparently accounts in large part for the relief of the ridge above the normal level of the ocean floor. As the Earth's mantle loses this excess heat away from the ridge crest, the sea floor sub- sides to its normal depth, but this process of cooling takes several tens of millions of years. This broad swell in the ocean floor forms a median ridge through the Atlantic and Indian oceans. This median po- sition is almost precisely true for the Atlantic, where it faithfully follows the contours of the opposing continen- tal slopes. The feature was first described and studied in the Atlantic and was appropriately termed the Mid- Atlantic Ridge. It is high, rugged, and marked by a prominent dorsal cleft, or rift valley. The ridge has a similar aspect in the Indian Ocean, although it is con- siderably more complex. Its overall form is like that of an inverted Y, but nevertheless the ridge maintains a rough- ly mid-ocean position relative to the surrounding conti- nents. The midocean-ridge system of the Atlantic and Indian oceans south of Australia joins with the East Pacific Rise (Albatross Cordillera). In the Pacific it is common prac- tice to use the term rise rather than ridge, because, al- though this rise is simply an extension of the midocean- The East Pacific Rise 792 Ocean Basins 435 Greatest ocean depths ridge system of the other oceans, the Pacific swell has a smooth, low silhouette and generally lacks an axial rift valley. The fast Pacific Rise also does not occupy a mid- ocean position but runs north-south, paralleling South America and intersecting North America at the mouth of the Gulf of California. This rise remains deeply sub- merged, and its presence is suggested by only a single volcanic ishmd rising from its crest, Easter Island. The difference in topographic expression between a ridge and a use has been explained in terms of plate tectonics. Fast spreading, defined as the opening of the sea floor at a rate faster than six centimetres (two inches) per year (or three centimetres [one inch] per year on each spreading limb), as is characteristic of the Pacific, produces a rise. Slow spreading, on the other hand, re- sults in the formation of a ridge. Sea-floor spreading is a symmetrical process that accretes new ocean floor equal- ly to both Hanks of a rift; when a former landmass splits apart, the ridge maintains a median position as the newly created ocean basin increases in size. This phenomenon occurred in the Atlantic and Indian oceans, but, in con- trast, the rise in the Pacific did not rift a landmass when it was formed, and consequently there is no reason for it to be median. Trendies. Oceanic trenches are long, narrow, arcu- ate depressions in the ocean floor. They occur prin- cipally around the periphery of the Pacific Basin, but examples aie also found in both the Atlantic and Indian oceans. Individual trenches have lengths of thousands of kilometres, widths of roughly 100 kilometres (60 miles), and depths of two to four kilometres (one to two miles) below the adjacent ocean floor. Nearly all of the hadal regions, which are those deeper than 6,000 metres (20,000 feet), lie within ticnches. Their continuity is remarkable— 9,000-metre- (30,000-foot-) deep Tonga Trench is about five kilometres (three miles) wide, but it is continuous for 700 kilometres (400 miles). Typically, trenches have an asymmetrical V shape with a steeper slope towaid land and a gentle slope toward the ocean basin; a low aich sometimes intervenes before the normal deep ocean floor is attained. Trenches and their asso- ciated island arcs, surmounted by explosive volcanoes, are the most active geological features on the face of the Earth. The great earthquakes and tsunamis (gieat sea waves produced by submarine earth movement or vol- canic eruption) generated from them are invariably asso- ciated with trenches. The greatest depths are found in trenches and so are near continental margins or island arcs rather than in the middle of the ocean basins. The deepest depression is the 10,850-inetre (35,600-foot) Challenger Deep, discovered by hms "Challenger II" in 1948, in the Mariana Trench not far from Guam. Some greater depths for this deep have been claimed, but they remain unsubstantiated. The oceanographcrs Jacques Piccard and Don Walsh de- scended to the bottom of the Challenger Deep in 1960 aboard the bathyscaphe 'Trieste," a feat comparable to the ascent of Mt. Everest. Some other great deeps of the Pacific arc Tonga Trench, 10,800 metres (35.400 feet); Kermadec Trench, 10,800 metres (35,400 feet); and Philippine Trench, 10,030 meties (32,900 feet). The greatest depth in the Atlantic Ocean is 9,200 metres (30,200 feet), found in the Puerto Rico Trench, just north of that island. It is now commonly agreed that trenches are subduct ion zones — that is, zones where the outer, 100-kilometre- (60-mile-) th'ek outer shell of the Earth plunges into the mantle at angles from 30° to nearly vertical. The bending of this rigid crustal plate in adapting to the spherical geometry of the Earth is the cause of the arcuate shape of the trench. The descending litho>pheric plate contains numeious rock types that are unstable in the regime of high pressures and temperatures that exists in the mantle. Hence, they cannot be consumed and are melted and returned to the surface as magmas and lavas that build up the arc behind the trenches. The Aleutians-Alaska Arc, which lies behind the Aleutian -Islands, is a prime exam- ple; the Kuril and Mariana arcs are others (see further ISLAND AKCS). Fracture zones. Since the early 1950s, bathymetric surveys have revealed a laigc number of horizontal linea- tions of high and rugged topogiaphy called fracture zones. These are long, narrow ridges and depressions that usually separate oceanic tidges of different depth. The fracture zones may be as much as 100 kilometres (.60 miles) wide and 2,000 kilometres (1,000 miles) long. The first to be described was the Mendocino Fracture Zone, extending westward for 3,300 kilometres (2,100 miles) from Cape Mendocino, California. Subsequently, three other almost parallel extensive fracture zones have been surveyed off western North America — namely, the Murray, Molokai, and Clarion fracture zones. These ap- pear to be scarps associated with offsets of a former ex- tension of the East Pacific Rise, which was overridden by the westward drift of North America. In the Atlantic Basin there are also numeious fracture zones that olfset the axial rift of the Mid-Atlantic Ridge. These fracture zones also extend far beyond the limits of the offsets and, in some cases, can be traced nearly to Africa or North America before their trace is lost beneath the thick-lying blanket of sediments along the continental margins. Earthquake activity indicates that these fracture zones are actively shearing (moving) today only where they connect segments of actively spreading ridges or where they connect a rift to a trench. The extensions of the fracture zones onto the adjacent segments of the ocean floor are dead (immobile), although the rugged relief along their trends remains as evidence of earlier faulting and cuistal slippage. Seamounts and guyots. A seamount is a mountain be- Mountains neath the sea, generally in the form of an isolated, conical beneath elevation of the sea floor at least one kilometre high, the sea Seamounts are the most prominent and sti iking features on the ocean floor. More than 2.000 seamounts have been reported, and many more await future discovery. There remains no doubt that seamounts are nearly all volcanoes (mostly extinct), because when dredged the bedrock is always basalt, and their shai>es and slopes tire like that of a volcano on land. They are composed of alkaline basalts derived from depths of 150 kilometres (90 miles) or more within the deep portion of the upper mantle. The Northeast Pacific Basin is especially rich in sea- mounts that commonly trend northwest to southeast in long festoons. Many of these chains arc entirely sub- merged, such as the Magellan Seamount Group in the far western Pacific. Others, such as the Hawaiian chain, are mixed groups of islands, banks, and seamounts. Forming an extension of this chain is the giant, deeply submerged Emperor Seamount Chain off Japan. Each of these sea- mounts is named after a semi-mythical Japanese emperor. Oceanic islands, those rising from the deep ocean bed beyond the continental shelves, may be classified as either high islands or low islands. High islands are simply the tops of giant seamounts that are both tall enough to pierce the surface and young enough not to have been eroded away by wave action. These are nearly all active, dormant, or recently extinct volcanoes, because erosion reduces an island to a shallow bank after a few million years. Strings of islands, such as the Hawaiian chain, may be formed when the Earth's outer crust drifts over a deep, stationary lava pipe. Thus, the volcanically active island alwa>s lies at one end of the chain. Low oceanic islands, those lying essentially at sea level, generally are coral atolls in tropical latitudes. As Darwin surmised about the mid-iyth century, these atolls have formed by the deposi- tion of limestone upon a subsiding, extinct volcano. The upward growth by corals and lime-secreting algae offsets subsidence and maintains the atoll precisely at sea level, so that these limestone edifices are "the gravestones of departed volcanic islands." Some large, deeply submerged seamounts, especially in the central North Pacific, are flat-topped and are termed guyots, after Arnold Henry Guyot, a 19th-century Swiss- Li. S. geologist. An especially large cluster of guyots is that of the Mid-Pacific Mountains, which stretch from west of Hawaii to Wake Island. ' Because truncation of a seamount can occur only by wave action at sea level, guyots are thought to be 793 436 Ocean Basins drowned ancient islands that have subsided one or more kilometres beneath the sea surface. They are found in regions unfavourable to coral growth, so that no atoll was built up to offset their subsidence. This sinking usu- ally is largely a result of regional subsidence of the ocean floor and of the horizontal drift of the seaniount as the ocean crust moves down the (lank of a rise. Local subsi- dence, or foundering, caused by the load empb.eed on the crust by a volcanic seamount, may also play a role, but sinking caused by a lelutivc rise of sea level (addition of new water to the oceans) apparently is not important. Although the oceans probably are growing deeper with time as new water is squeezed out of the Earth's mantle, this deepening is exceedingly slow, probably not more than a few centimetres per million years. Abyssal lulls and plains. Hills and knolls on the ocean floor aie termed abyssal: they are protuberances smaller than seamounts, rising to heights from a few tens to several hundred metres above the ocean floor in regions largely devoid of sediment. Extensive regions of chaotic roughness especially characterize the Pacific floor along the flanks of the midocean ridges. Where careful surveys have been made, these hills commonly display an elon- gate form. They are caused by faulting of the oceanic crust, volcanic extrusions, and other kinds of deforma- tion. Featureless Extensive regions of the ocean floor are abyssal plains, plains flat, featureless, sedimentary plains with slopes of less on the lhan one part in 1,000. Over broad reaches these plains sea floor will not vary in depth by as much as one metre, and they are the lcvelest regions on the face of the Earth. This nearly perfect flatness is derived by the long-continued deposition of sediments by muddy bottom flows, which pond in the deepest hollows, burying any existing irregu- larities. These plains are found in all ocean basins but are best developed near continental margins and in the Atlan- tic Ocean, where deposition rates aie high. Fine examples off the eastern United States are the Hatteras and Nares plains, lying at 5.5 kilometres (3.4 miles) depth, which have been developed by sediments shed from North Ame'ica. The world's gicalest abyssal plain is probably that underlying the Bay of Bengal, which has been built up by the muddy Ganges and Irrawaddy rivers. Sediments of lite ocean floor. The ocean floor is blan- keted in most places with a sedimentary cover. Two basic types are recognized: namely, terrigenous sediments (sands, silts, and clays) that are shed from the continents or from islands and pelagic, or open-sea sediments — the finely suspended clays and remains of pelagic (floating- form) plants and animals that "rained" gently on the bottom. The terrigenous sediments generally arc deposited near the base of the continental slope as sedimentary fans or aprons. They are mostly turbidites laid down by turbidity currents (a type of density current in which the density contrast arises because of the high sediment concentra- tion of the flow), and they attain great thickness. Al- though covering a laiger area, the pelagic oozes form a thinner blanket (zero-two kilometres thick). The most common is globieerina ooze, composed of minute cal- cium carbonate shells of protozoans, mostly of the genus Globigaina. This ooze covers vast expanses of the Atlan- tic and Indian oceans. Calcium carbonate dissolves in the deeper portions of the oceans so that in much of the central Pacific Basin calcareous oozes are replaced by red clay. Diatom ooze, composed of opaline siliceous shells of marine algae, are found mainly beneath colder waters. A belt of diatom ooze cordons the world in the Antarctic region, and another zone lies across the far north Pacific. Another siliceous ooze, radiolarian ooze, is typical of tropical regions. A belt of this ooze extends across the Pacific beneath equatorial waters. It is composed of the minute remains of radiolarians, a pelagic protozoan (see flllther MARINE SEDIMENTS). Basin boundaries. Continental slopes. The outer edge of the continental slope is maiked by an abrupt brink where the sea floor plunnes three to fi\c kilometres (two to three miles) to join the abyssal floor. The continental slopes are the longest, highest, and sti .lightest boundary walls in the world. Only the lofty Himalayan rampart facing India attains the scale of a continental slope. If the ocean waters were removed, the continents would stand as pedestals everywhere. The continental slopes are the margins of the continents and, hence, are the boundaries of the ocean basins. Their declivity is typically 3° to 5°. Some continental slopes can be classified as accretion- ary, because they were created by oceanic crust under- th i listing the continental margin. This origin applies to much of the Pacific margin. Other slopes are modified scarps or faults related to continental breakup and conti- nental drift. This origin applies to much of the Atlantic and Indian ocean margins. Such slopes have commonly been extensively modified by sedimentation. The continental rise. In many parts of the world the continental slope is separated from the abyssal ocean floor by a broad apron. This continental rise is the lop of a prism of sediments shed from the continents and laid down mostly by turbidity currents on the deep ocean floor. Such rises arc particularly characteristic of the At- lantic and Indian oceans. A particularly fine example is developed off the eastern United States, extending as a smoothly sloping apron for about 250 kilometres (150 miles) from the 1,000-fathom (2,000-metre [6,000- foot]) level to the deep abyssal plain. Geophysical inves- tigations indicate that this continental-rise prism may at- tain a thickness of more than six kilometres. This huge sedimentary prism is regarded as a potential major oil province of the future. After initial deposition by turbidi- ty currents, the sediments of the continental rise may be extensively reworked and are deposited by deep bottom currents. This condition is particularly true along the western sides of an ocean basin. The Blake Nose, a huge lens of sediment projecting outward from the continental rise off the south central United States, is an example of this bottom-current effect. Because the deep currents tend to move parallel to the bottom slope, they are called contour currents and their deposits contourites. ORIGIN OF OCEAN BASINS The new concepts of plate tectonics and sea-floor spread- ing have worked a revolution in the Earth sciences. Among other things, the concepts provide an adequate explanation for the origin of ocean basins. The theory holds that the Earth's outer shell is broken into about eight large, rigid, spherical caps, plus many small sub- plates. Except for the Pacific plate, which includes much of the Pacific Ocean, each major plate contains a separate continent embedded within it. An ideal plate may be envisioned as being rectilinear. Along one edge, where the plate is heavy, it dives into the Earth's mantle along a trench called a subduction zone. Opposing this zone of lithospheric descent, a rift is formed. As the rift grows larger, the void left behind is constantly healed by the upwelling of mantle rock that emplaccs new ocean crust, a process known as sea-floor spreading. New ocean crust is presently being generated at about 1.5 square kilometres (0.6 square mile) per year, a rate sufficient to repave the entire ocean basin in 200,000.000 years. To accommo- date this crustal movement, the rift and the trench are connected by large zones of shear or slippage called transform faults. Thus, crust is consumed at the trenches, created at the rifts, and conserved along the transform faults. The crustal plates and the continents embedded within them undergo drift, and this condition provides the mechanism for continental drift (q.v. ). Typical drift rates range from one to several centimetres a year, a remarkably rapid geologic process. To understand why the Earth has ocean basins, the ori- gin of continents must be considered, because the ocean basins are simply those depressed crustal regions that lie between the isolated continents. The continental plateaus are slabs of granitic rock or sial (siliceous or acid igneous rock), and they literally float in the Earth's denser mantle like blocks of wood floating in water. Following the prin- ciple of Archimedes, the continents adjust themselves to a level at which the weight of the mantle rock displaced is equivalent to their own weight, which is called isostatic (equal-weight) equilibrium. The 35-kilometre (22-mile) Formation of ocean basins between the continents 794 Ocean Currents 437 thickness of the continents and their density contrast with sinia (mantle rock) is such that a five-kilometre (three- mile) relief results between oceanic and continental lev- els The generation of the pranitoid rocks that form the continents requites at least two stapes of melting and gravitational differentiation (separation according to density dilTeiences) of the low-density rock from Ihe heavier lock, hirst, as the midocean rifts pull apart, new oceanic basalt fills in the void, repaving the ocean floor. This basalt is a partial melt or differentiate of the primi- tive, heavy, ultrabasic material of the Earth's mantle. Because of crustal drift this basalt is eventually consumed within trenches, subduction zones that carry the crust downward into the hot regime of the upper mantle. There the oceanic basalt is remelted, giving olf sialic (lighter) rock thai rises up to the surface as lava or granitic intrusions. This new rock generally forms an island arc that ultimately becomes accreted to the margin of a conti- nent. In this manner the continents grow and the regions between these sialic plateaus become the ocean basins. BIMJOGltAPHY. The literature on the ocean basins is ex- tensive and is growing at a rapid rate. Only a brief sampling of English-language publications can be included here. Some general nontechnical discussions about the ocean floor are: B.C. heezgn and CD. not LISTER, The Face ol the Deep (1971 ), a magnificent monograph of deep sea photo-, whh explanatory text; r.p. sufpard, The Earth Beneath the Sea (1959), which emphasi/cs the geomorphology of the ocean floor; d.h. and M.P. tarling, Continental Drift (1971), summarizes the now accepted concept of drifting continents in terms of plate tec- tonics; H.w. menard, Anatomy of an Expedition (1969), tells how a modern scientific expedition is organized to study a portion of the Pacific Basin. Some popular books that deal with the oceans generally are: J. dugan, Man Under the Sea, rev. ed. (1965), which concerns man's entry into the subsur- face world; and J. piclakd and R.s. diet/, Seven Milc< Down (1961), a documentary account of the bathyscaphe "Trieste" and its ultimate dive to the bottom of the Challenger Deep. Sonic important textbooks and basic reference works include the following: The classic text on oceans generally is by II. U. sverdrup, M.W. Johnson, and R. Fleming, The Oceans (1942). An excellent treatment of the Pacific is presented by H.w. menard in Marine Geology of the Pacific (1964). P.P. S1IUPARD, Submarine Geology, 2nd cd. (1963); and P.H. KUE- nen, Marine Geology (195(1), discuss the ocean floor gener- ally. Erosional forms are covered in f.p. sniPARn and R.F. DILL, Submarine Canyons and Other Sea Valleys (1966). The mineral potential of the ocean floor is described in j.L. Mi-RO, Mineral Resourced of the Sea (1965). Some more general reference works are: R.w. FAIRBRIDGE (ed.), Ency- clopedia of Oceanography (1966); and M.N. iull and A.E. maxwell (cds.), The Sea, 4 vol. (1963-70). Charts of the coastal regions of the United Stales may be obtained from National Oceanic and Atmospheric Administration (noaa), National Ocean Survey, Washington, DC; chart and bathymetric maps for other countries arc issued by the Naval Oceanographic Office, Washington, D.C. Physio- graphic maps of the Atlantic, Pacific, Arctic, and Indian oceans may be obtained from the National Geographic So- ciety; and original oceanographic data for selected regions is available from noaa, Environmental Data Service, Na- tional Oceanographic Data Center, Kockville, Maryland. (R.S.D.) Ocean Currents The great water masses that cover nearly 71 percent of the earth's surface are interconnected by a rather orderly system of ocean currents. The driving forces for this water motion aie w ind friction at the sea surface and horizontal and vertical differences in the density of scawater. Dif- ferential heating and cooling, precipitation, and evapora- tion pioduce differences of water density at the sea sur- face Overturning of water masses, vertical convection, and mixing provide the mechanisms foi distributing densi- ty differences from the sea surface into deeper layers. This creates horizontal density differences and, conse- quently, horizontal pressure differences and currents at all depths in the oceans. As far as the driving forces arc concerned, a distinction is made between these two com- ponents of the general oceanic circulation (wind friction and differential density); they ate not independent of each other, however. Because the oceanic circulation is so closely linked to the atmosphere and its behaviour, the great oceanic current systems cannot be as stable or as steady as might be expected. The usual charts depicting ocean currents show only the prevailing current directions and speeds, not their variability. Such charts represent the average trend of water displacements and are comparable to climatic wind charts. This article treats the nature, distribution, and causes of ocean currents and oceanic circulation, and oceanic-at- mospheric interactions, including climatic effects. Relat- ed aspects of these topics are discussed in the articles vvatfk waves; tidls; oceans and seas; atmosphere; winds and storms; and climate. DISTRIBUTION OF OCEAN CURRENTS Charts that show the horizontal distribution of ocean cur- rents are based on a large number of direct and indirect current observations. Most of the data are obtained from ship drifts, however. If careful record of the course and speed of the ship is made then a "dead reckoning posi- tion" is established. I his would be the true position if no drift by currents has aflected the course and speed of the ship. The difference between dead reckoning and the actual position as determined by astronomical or elec- tronic means indicates the average current. Whenever possible, these differences are determined at least 24 hours apart. The general pattern of currents throughout the world's oceans is shown in Figure 1 for the Northern Hemisphere winter. More detailed maps are available for individual oceans or for paits of the oceans, and the adjacent seas. Figure 1 shows that the distribution of currents in the upper strata of the oceans tends to coincide with the pre- vailing winds of the world. It should be recognized, how- ever, that this smooth, average representation of the oceanic circulation only outlines the general trend of hori- zontal water movements. Because ocean currents are three-dimensional water dis- placements, the vertical components of currents are also of interest. In general, vertical speeds arc much smaller than horizontal speeds. Nevertheless, vertical motions are important for an accurate description and explanation of the oceanic circulation system. Significant vertical blanch- es in the current structure occur mainly where horizontal currents cither diverge or converge. The phenomenon of upwelling water in the surface strata of the oceans is caused by diverging surface currents in the open ocean, or near the coasts of continents where a supply of water from deeper layers is required to compensate for the sea- ward motion of surface currents. The formation and spreading of water masses in the deep sea also depends upon veri.cal branches in the current system for explana- tion. THE CAUSES OF OCEAN CURRENTS The equations of motion in hydrodynamics make use of one of Newton's fundamental laws of mechanics when applied to a continuous volume of water. They state that the product of mass and current acceleration equals the vector sum of all forces that act upon the mass. Besides the external force of gravity, the most important forces that cause and affect ocean currents are horizontal pressure gradient forces, the Coriolis forces, and friction- al forces. Pressure gradients. The hydrostatic sea pressure, p, at any depth below the sea surface is given by the product A = g f> z, where g is the acceleration of gravity, p is the density of seawatcr, and z the depth below the sea sur- face. Because differences in density at any fixed depth are due to differences in temperature and salinity, the sea pressure, p, will vary correspondingly from region to re- gion. This part of the total internal pressure field in the oceans is called the relative field of pressure. In a homogeneous ocean of constant potential density, horizontal pressure differences are only possible if the sea surface is tilted against level'surfaces. Level surfaces are everywhere perpendicular to the force o'f gravity (the plumb line). In this case, surfaces of equal pressure, called Vertical com- ponents of currents 795 T Diets, R.S. 0974) The oceans frcm Sky lab /+. Sea Frontiers, v. 20, no, 6, p. 359-363, nov-oec e Oceans from S&yfa 7 By Roberts. Dietz NO A A Atlantic O'ceanographic and Meteorological Laboratories Miami, Florida Skylab 4, man's longest mission in space, has produced a wealth of spectacular photographs from near- space, providing a new perspective of our earth. In all, more than 2,000 photographs were taken, using a hand- held 70-millimeter Hasselblad and a 35-millimeter Nikon. With astronauts Colonel Gerald Carr, Dr. Edward Gibson, and Colonel William Progue. Skylab circled the earth once every 93 minutes for 84 days between No- vember 10, 1973 and February 1, 1974, completing a total of nearly 1,500 revolutions. Quite naturally, most effort was devoted to land photography, but many excellent views also were obtain- ed of coastal zones, oceanic islands, and the open sea. The orbital inclina- tion was 50° so that the astronauts could see nothing beyond 50°N. or 50°S., but could sec all of the earth in between. The same sequence of flight paths was reoccupied every 7 I revolutions (5 days) so that changes in ice patterns, etc., at some particular site could be noted. Thus, the astro- nauts monitored the build-up of sea ice in the Gulf of St. Lawrence and the drift of icebergs in the South Atlantic. Many unusual occanographic phe- nomena were noted for the first time. The confluence off Argentina of the cold Falkland Current with the warm Brazil Current was traced eastward to- ward Africa for 2,200 miles (3,500 kilometers) with the boundary being marked by eddies and ring currents. Elsewhere, the astronauts noted subtle discoloration of the sea caused by plankton blooms. It proved especially useful to peer at sea surface slicks in the area of sun glint (the aureole of sun reflection) as their curious pat- terns revealed macrotuibulence swirls, internal waves, and windshear effects. ©Florida and the Straits of Florida (See photograph on next page.) The southern tip of Florida shows (a) the greater Miami metropolis, (b) Biscaync Bay, (c) the Everglades, (d) Florida Bay, and (e) the Florida Keys. Fringing Florida in a graceful arc is a slightly submerged chain of coral reefs, the only living reefs in the United Stales mainland. On the right margin of the photo is the island of Bimini in the Bahamas. The sinuous lidgc to the south of this island is the famous oolite banks composed cf pure aragonitc pellets. These deposits are November-December 1974 359 796 797 currently being mined for use in the manufacture of cement and other products requiring unusually pure lime (calcium carbonate). The light- colored circular region in the bottom center of the photo in the area of sun glint is Cay Sal Bank, nearly all of which is under water. Between Florida and the Bahamas lie the the Straits of Florida, which is the site of the major arm of the north- setting Gulf Stream, the world's most remarkable planetary current. A sec- ond arm of the Gulf Stream flows along the open Atlantic side of the Bahamas, merging with the Florida Straits flow over the submerged Blake Plateau to the north (not shown). With a flow rale averaging 3.5 knots, the Gulf Stream is one of the world's fastest and, with a total flow of 70 sverdrups, it is one of the mightiest currents. (A sverdrup, named after Harald Sverdrup, a famous Norwegian oceanographcr, is a measure of flow equal to 1 million cubic meters per second. By comparison, the Missis- sippi has a flow of 0.02 sverdrups, so that the Gulf Stream flow is 3.500 times greater. All of the world's rivers have a total flow of about 2.0 sver- drups.) That portion of the Gulf Stream that flows through the Straits of Florida is rated at 30 sverdrups. Oceanographers have recently discov- ered a weak south-setting underflow along the bottom near the Florida margin. The spinning of the earth causes a shift of warm water to the right in the northern hemisphere, i.e., toward Bimini where the sea level stands 10 inches (25 centimeters) higher than off Florida. Thus, there is a slight, but measurable, tilt of the sea's surface. The Gulf Stream flow is due, in part, to a hydraulic head as the waters stand 4 inches ( 1 0 centimeters ) higher in the Gulf of Mexico than in the Atlantic Ocean. This unbalance is created by the southeast trade winds that push water into the Gulf of Mexico. ©The Island of Hawaii A near- vertical view of Hawaii (the Big Island), the world's greatest vol- cano, from Skylab 4. Snow-capped (a) Mauna Kea and (b) Mauna Loa both rise more than 1 3,000 feet (4,000 meters) above sea level and over 33.000 feet (10,000 meters) above their ocean-floor bases making them the world's tallest mountains. Mauna Kea is a recently extinct volcano, while Mauna Loa and (c) Kilauea (barely discernible) are the active centers of lava effusion. Within the white snow aureole of Mauna Loa, the summit caldera is clearly evident. These Hawaiian volcanoes, along with Iceland, appear to generate more than one-third of the world's lava. Vivid color variations clearly depict the suc- cession of lava flows — the dark-brown streaks around Mauna Loa are the youngest flows, while the older flows appear more green owing to a cover o." vegetation. The western coastline, exposed to the onslaught of large waves, is etched in white while little evidence of breaking swell can be seen along the eastern leeward coast. The V-shaped reentrant along the nordicastern coast is Hilo Bay at the base of which lies (d) Hilo, the capital city of the Big Island. Hilo has the dubious distinction of being the world's most likely city- to suffer November-December 1974 361 798 799 damage from tsunamis (sometimes erroneously called "tidal waves"). Appropriately, it is the center of the Pacific tsunami warning system. ©Northern Gulf of California This view, photographed by a Sky- lab 4 astronaut, is westward looking from the Mexican mainland, across Baja California and into the open Pa- cific, where the cold California cur- rent moves sluggishly southward. Up- wclling along this coastline brings nutrient salts to the surface waters, making these waters highly productive of sea life. The Gulf of California is also highly productive, as the Colo- rado River, the delta of which can be seen at the center along the right margin of the photo, brings in nutri- ents from the land. Unfortunately, this outflow of water has been largely stemmed in recent decades by the use of the Colorado River for irrigation in the Imperial Valley of California and elsewhere along the river basin. The addition of nutrients causes an intense springtime bloom of phytoplankton so that diatom ooze now covers much of the bottom of the gulf. Some of the world's largest tides, up to 33 feet ( 10 meters ) , surge into the gulf's apex. On the far side of Baja California is Ojo dc Liebre (Scammon's) Lagoon. About 5,000 California gray whales, Eschrichtius gibbosus, migrate south each January and February from the arctic seas to give birth to their young within this sheltered lagoon. A great transform fault runs through the axis of the Gulf of Cali- fornia, entering the mainland beneath the Colorado River delta. It separates the Pacific crustal plate from the North American plate and is an extension of the famous San Andreas fault of Cali- fornia. Slippage along this fault car- ries Baja California northward relative to the mainland at a rate of 2.5 inches (6 centimeters) per year. Spreading zones along this fault have opened the gulf by rifting it from the mainland over the past 15 million years. O Internal Waves off the Magdalena Delta The Magdalena River pours a mud- dy plume into the sea off northern Colombia. The plume is carried west- ward into the western Caribbean Sea under the influence of the southeast trade winds. Revealed for the first time, and still a puzzle to oceanogra- phers, are several fields of giant inter- nal waves presumably caused by tidal excitation of the thermocline — the boundary zone between the warm sur- face water and deeper cold water. (The lighter spots with accompanying shadows are groups of clouds while the more subdued and regular wave patterns arc the internal waves.) An unseen but immense submarine can- yon is incised into the submarine portion of the delta immediately off the river mouth. This chasm has been the site of frequent undersea avalanches, mud flows, and turbidity currents, which commonly break submarine telephone cables along their route. The cities of (a) Barranquilla and (b) Cartagena can be vaguely discerned. November-December 1974 363 800 1G, ocean deep The roles of the sea in relation to human life are many. Planet Earth is Planet Ocean for the waters really dominate our sphere. To fathom-high man, the ocean seems enormously deep and an endless frontier. But, as the world grows smaller and its population larger, the role of the sea is changing. bz:z:ji::z:z: •• U^S^^%:i^^^ZKSS^m^?.S-fiT^SffPt^f.yft ■ sfcijj !-. ...> .y- •, .y. -• ■AA^r Dr. Robert S. Dietz, NOAA Atlantic Oceano graphic and Meteorological Laboratories Life originated in the sea, and without the sea all life would cease. Because of the high specific heat of water, the oceans act as a great global thermostat and heat reservoir, leveling out the extremes of temperature that would prevail without its moderating influences. The sea's surface provides an avenue for the least-expensive mode of transport known. But it has also been a barrier— for example, keep- ing Creat Britain free from foreign invasion since 1066 A.D. The shore provides a playground, and the open sea is the ultimate repository for all hu- man waste. Ocean fisheries are a major source of food. Less appreciated is that the sea is a major storehouse of minerals. Even today the value of oil recovered from the continental shelves around the United States exceeds the income of fisheries. While the undersea world is our nearest frontier, it is also the most distant. It lies at our feet but it remains unknown— virtually un- explored and unused. Plate tectonics and continental drift In the past decade we have achieved a new model of the earth, based upon plate tectonics and its corollary of continental drift. This new paradigm of global tectonics has been as revo- lutionary to earth science as Darwin's theory of evolution was to biology a century ago. We now know that the earth's crust consists of a mosaic of about eight major crustal plates which are in relative motion. New ocean floor is born and accreted to the plates along the mid-ocean ridges by a process of dike injec- tion which we have called sea-floor spreading. New crust is offset by the consumption of old crust which descends by subduction into the deep-sea trenches mostly around the Pa- cific Ocean. Connecting the ridges to the trenches are zones of shear called transform faults. The continents are embedded within these plates so that they drift passively. North Amer- ica, for example, is drifting westward about 2 cm per year— approximately the rate at which one's fingernails grow. This may seem ponderously slow, but it is a remarkably rapid geological process. Without doubt, plate tectonics has been the major payoff resulting from the support of oceanic research by our federal establish- ment. In years to come, plate tectonics will play an enormous role in exploiting mineral resources both at sea and on land. It is difficult to assess fully the importance of this new insight into how the earth really ticks. Any attempt to do so would be like trying to determine the value of knowing the earth is round rather than flat. The concept has been a triumph of marine geology and geophysics because most of the evidence and virtually all of the plate boundaries lie beneath the sea. Mineral resources The rising standard of living of man every- where has placed great emphasis on expand- ing the extraction of mineral resources. As with food, man would like to turn to the sea. But the outlook is not bright. Prospect would be much better if the ocean floor were an ancient terrane like the mineral- rich Precambrian shield of Canada— as many geologists thought, as recently as a decade ago, that indeed it was. In terms of plate tec- tonics, we know that the ocean crust is com- posed of basalt (congealed lava). In basalt, the metals are too evenly and thinly diluted to form ore deposits. There are, of course, exceptions— on the sea bed we find extensive fields of phosphorite concretions and manganese nodules with a high content of copper, nickel, and cobalt. Hy- drothermal deposits of base metals also have INDUSTRIAL RESEARCH— NOV 15, 1974 801 been identified, associated with hot brine pools in the Red Sea. Any exploitation of these deposits, however, would require an enormous capital investment. I do not intend to denigrate the eventual future potential of manganese nodules. They will doubtless one day become an important ore for several base metals. A large zone of these nodules has recently been delineated far south of Hawaii and overlying the radio- larian ooze belt of the Pacific. They have contents of nearly 2% for both copper and nickel. Such deposits would certainly be ores on land today but the cost of sea mining is high. South African diamond operations, for example, reveal that it costs five times as much to recover alluvial diamonds from the continental shelf as by strip mining on land. The only deep-sea mineral deposits, if we may properly call them so, now being ex- ploited are the deep-sea precious corals. Jap- anese fishermen recover these in tangle dredges from the slopes of Pacific seamounts. There is one bright hope which remains vir- tually unappreciated. This is the potential re- covery of oil from the continental-rise sedi- mentary prisms. These areas lie along the base of most continental slopes of the world e.g., the slopes along the Atlantic margin of North America. (I refer here not to oil de- posits on continental shelves which are cur- rently being exploited. I refer rather to deeper deposits adjacent to the continental slopes overlying the abyssal ocean floor.) There is every reason to suppose that these giant prisms, the largest sedimentary deposits in the world, are petroliferous. The basic con- ditions for oil accumulation are met— source hods, porous reservoirs, stratigraphic traps, young sediments, and absence of appreciable thermal or dynamic metamorphism. In any calculation of the world's petroleum reserves, these giant prisms are ignored be- The sea against hunger There has been much sunny prose written about the sea as a vast cornucopia for feeding the earth's exploding population. In reality, the oceans lack this potential and there is little hope of changing this condition. At present, the oceans, yield about 70 million tons of fish products— about 4% of the world's food supply. This yield may conceivably be dou- bled or tripled, but only at a greatly increased cost per ton of fish. Perhaps the brightest hope is to tap the wholly unutilized crop of antarc- tic krill, Euphausia superba. The krill is a shrimp-like planktonic animal which is essen- tially the entire food of the baleen whales. But any gains in fish landings are currently offset by population growth. The spectre of mass starvation will continue to stalk the earth until our population is stabilized. We need not look far to understand this dilemma. Per unit area the organic production, of the ocean— that is, the amount of carbon fixed into living tissue— is only about one half that of the land. The oceans, being twice as extensive as the land, therefore, produce only an equivalent amount of plant matter. Most of our food, however, comes from the seeds, tubers, etc., of the flowering or vascular plants such as abound on land but which are com- pletely absent from the open ocean. Except for such nearshore flowering plants as eel grass, surf grass, and turtle grass, only algae live in the sea. Even if these were usable as food, they are so thinly dispersed and the standing crop at any particular time is so low that their collection is not feasible. We must INDUSTRIAL RESEARCH— NOV 15, 1974 802 "V*1"-":- J^4i^^ seraa .; vv'V rely upon fish and shellfish to convert the algae into food usable for man. On land we derive our food primarily at the first trophic level. That is, we eat starches and sugars derived directly from plants. Only the more wealthy nations such as the United States can afford to obtain much of its nourish- ment at the second trophic level— that is, eat cattle which, in turn, have fed on grass. But when we eat tuna, we are being nour- ished at the fifth trophic level. Tuna feed upon small fish, which feed upon euphausiids, which feed upon copepods, which feed upon algae (diatoms). There is a factor of ten loss of food value at each succeeding higher trophic level. Thus ten thousand pounds of algae are needed to generate one pound of tuna. For diis reason, the seas can never supply an abundance of inexpensive food. It can only supplement our basic carbohydrate diet with an excellent source of low-fat protein. Contrary to expectation, it apparendy is easy to overfish the oceans. Fishing grounds are highly localized, and most of the ocean is a biological desert. Examples of disastrous de- clines in fisheries are legion. A case in point was the virtual disappear- ance of the California sardine (actually a pil- chard) fishery after World War II. Overfishing was apparently an important factor in this disaster, but an ultimate understanding re- mains elusive. Studies by John Isaacs of the Scripps In- stitution of Oceanography have shown a re- markable fluctuation in fossil pilchard scales and teeth in the sediments of the basins off California. This indicates there may be a natural cycle of changing pilchard abundance. In the past few years there has been a cata- strophic drop in the catch of large bluefin tuna in the North Atlantic. These, the largest of all the tuna, sometimes weigh in at 500 pounds or more and are the prize catch of sport fish- ermen. Landings are now off 98%. This short- age probably is caused primarily by intensive fishing pressure in die western North Adanb'c to supply the great demand from Japanese buyers. Tuna, eaten raw as sashimi, brings a high price as a delicacy in Japan. Marine mammals Seaquariums and TV shows have created a growing interest in marine mammals— baleen whales, toothed whales, sea lions, sea otters, etc. They are among the most intelligent of mammals. We are growing to regard them as creatures with which we can associate and not just simply slaughter for dog food. Knowing sea mammals better is beginning to affect our moral judgement. The world does not belong to man alone. Many of the sea mammals are endangered species— especially the baleen whales. Future generations may remember our generation as the one which discovered nuclear energy but also exterminated the blue whale, the largest and most magnificent animal that exists or ever has existed on earth. The blue whale is not gone but its numbers may be too low to ever stage a comeback. We can hope that its story will be like the California grey whale, which was thought to be extinct in the 1920s. Under full protection. the grey whale has survived and has increased its numbers steadily. The 1974 whale count off Monterey, California, showed 4,000 whales, the largest count ever, and the actual number is considerably larger. Other bright spots are the successful man- agement of the Pribolof fur seals and the comeback from near extinction of the Cali- fornia sea otter. The Navy and other groups have shown that sea mammals are remarkably tractable and trainable. They are easily domesticated and 60 INDUSTRIAL RESEARCH— NOV 15, 1974 803 i i - J J. . J, > ^K^A^JS^A ■& enjoy an association with man. This pertains not only to standard performers at seaquar- iums, such as the bottle-nosed dolphin ( Tursi- ops truncatus) and the California sea lion but to many other species as well. The killer whale (Orcinus orca) is revealed as a friendly and intelligent animal and not the killer it was reputed to be. The Navy has trained the pilot whale (Globicephala scam- mom) to boat-follow in the open sea and to retrieve objects from depths of nearly 2,000 feet. In all probability we will one day see even the great sperm whale trained to perform useful tasks nearly a mile down. Of great interest are the active sonars ap- parently shared by all of the toothed whales (the sperm whale, dolphins and porpoises). We can still only guess what the dolphin "sees" sonically, but we know it is a remark- ably detailed picture. Possibly his "view," or sonogram of a human swimmer is like an x-ray or radiographic image, for sound waves are not restricted to surface reflections. Dolphin sonar is certainly magnificent, but we can no more understand it than a blind man can envision the sense of sight. Some studies even suggest that one dolphin can read the mind of another. The fragile sea Man has recently begun to realize that our Earth is a fragile environment. Perhaps pacing this realization are the astronaut's photos of Earth from deep space. We also now know that we are alone on Spaceship Earth at least jwithin the solar system. \ Even a decade ago the sea was regarded ^as an endless frontier to be exploited and sub- jected to man's will. Hopefully, we now know ithat we must live with the sea in a symbiotic relationship. To do so successfully requires sophisticated understanding far in excess of 'present knowledge. Any schoolboy knows that the Gulf Stream keeps England warm. But is this truism really true? Would not England be equally warm if the clockwise gyre of the North Atlantic were suddenly reversed into a counterclockwise flow? (Of course, this would never happen short of reversing the earth's direction of ro- tation.) The Gulf Stream then would flow south, but warm current would flow northward from the tropics along the European margin. Would not England be equally as warm under this regime without the Gulf Stream? The point to be emphasized is that we are still far from any complete understanding of this most intensively studied of all ocean cur- rents. The ocean, like the land, is finite and we must guard against its pollution. But pollution is a loaded word. In a sense, the oceans have always been polluted— charged with salt. . It is proper to speak of the outfalls from nuclear plants as providing thermal addition to the sea and not thermal pollution. The over- all effect may be good rather than bad. And, in any event, it would seem to be a trade-off that man must accept for solving the energy problem. Certainly it is a poor use of petroleum simply to burn it for heating space. This most useful and limited fossil fuel should be saved for petrochemicals and for lubricants for the generations to come. It is ominous, that man's intervention has caused major changes in both the biology and the chemistry of the Great Lakes. Lake Erie is already seriously polluted under any definition of that term— and the other lakes are endan- gered. This is quite remarkable when we realize that their size is such that they contain about one quarter of all of the world's fresh water. Fortunately, the Soviets are seriously attempt- ing to safeguard Lake Baikal, which contains INDUSTRIAL RESEARCH— MOV 15, 1974 61 804 an equivalent amount of fresh water, from pollution by pulp mills. To the layman, one bucket of sea water seems just like any other. But the plankton, the fishes and the oceanographer know differ- ently. Life can flourish in one region but not another— both in general and for any particular species. The skeins of life are fragile and easily dis- rupted by the activities of man. Most commer- cial fishes, for example, must come into the shallows, estuaries or marshes at one stage in their life cycle. These areas are readily modi- fied by man's activities. Ocean fertility is based on the nutrient salts, especially phosphate and nitrate. Upwelling, which provides for much of the renewal of these fertilizers, takes place over only about one per cent of the ocean's surface. The most remarkable example of upwelling occurs off Peru, which in the past decade has become the world's leading fishery nation, producing a record twelve million tons of anchovies in 1970. Of late, the catch has dropped off. One won- ders if a disastrous decline will occur, follow- ing the pattern of the California sardine. Only time will tell. Last year the landings had dropped to two million tons. Both intensive fishing and the intrusion of a warm, south-setting current, called El Nino, had taken their toll. But in 1974, following strong management measures taken by the Peruvian government, including at times the complete banning of fishing, the anchovies seemed to have returned in abundance. A total catch of five million tons is anticipated for this year. Tampering with the seas In the years to come, man will either in- tentionally or inadvertently tamper with the sea. Hopefully it will be the former, not the latter. We will also witness increasing inter- national collaboration in studying the seas. In the summer of 1974 a multi-national air- sea interaction study was launched in the tropical Atlantic under the acronym of GATE (Global Atmospheric Research Program— At- lantic Tropical Experiment). At a cost of $53- million it probably is the most expensive expe- dition ever launched. Both the USA and the USSR are participating with ships and scien- tists at a cost of $18-million each. There are dreams, which easily could be- come plans, of tampering with the ocean cur- rents. Many of these flows are inexorable, like the mighty Gulf Stream which carries nearly fifty times as much water as do all of the rivers on earth combined. About 1912 the Congress of the United States was asked for an appropriation to build a barrier from Cape Race, at the tip of New- foundland, across the Grand Banks to obstruct the south-setting flow of icy arctic water. It was supposed that the Gulf Stream would then swing in nearer to the New England coastline and bring us warmer winters. For- tunately, the money was not provided, for there is little reason to suppose that the plan would have worked. Today there are those who propose placing huge impellors in the Florida Strait, tapping the four-knot current for the generation of power. A feasible plan, if not a wise one, would be to tamper with the flow through the Straits of Gilbraltar simply by raising the sill depth or damming it. Cool, low-salinity water flows into the Mediterranean at the surface. At depth, warm, high-salinity water pours out- ward with a flow ten times that of the Mis- sissippi River. This produces a warm mid- water tongue of Mediterranean water. This warm layer invades much of the eastern North Atlantic causing marked physical and eco- logical effects. Henry Stommel at the Woods Hole Ocean- ographic Institution has suggested that, by damming Gibraltar, the world's climate might be drastically altered. According to Stommel, the salinity of the Atlantic might drop. After 30 years, it might be no more salty than the Pacific. In turn, Arctic water might tend not to sink. The deep North Atlantic would then accept abyssal waters flowing in from the Antarctic. Such results would vastly change the abys- sal circulation of the oceans. A series of cur- rent modifications would then be triggered which would reduce the influx of warm water into the Arctic Ocean. The ice pack would grow. Then, if the Ewing-Donn theory of the Ice Ages is correct (contrary to one's intui- tion), this would lead to a decline of glaciers on land and a general warming of the earth. As Stommel points out, common sense rebels against accepting such a fantastic ef- fect from so small an intervention by man. Indeed the argument is loaded with unproved assumptions and tenuous speculations. Stom- mel admits that he could construct an equally plausible argument that such a damming would cool rather than warm the earth. The truth would seem to be that »uch speculations have a certain dreamlike quality. We need first of all to develop a better quan- titative understanding of oceanic circulation. Only then can such speculations be con- strained. Of course, Nature sometimes performs her own experiments. Coring by the Deep Sea Drilling Program has revealed a 3-km-thick layer of salt underlying the Mediterranean Sea. This was laid down in the late Miocene period about five million years ago. INDUSTRIAL RESEARCH— NOV 15, 1974 805 Apparently, inflow through Gibraltar was then so restricted that the Mediterranean be- came a saturated brine basin like the Dead Sea today. As evaporation continued, salt was precipitated and deposited subaqueously. This "salinity crisis" ended only when Gi- braltar deepened sufficiently to permit the highly saline waters to reflux back into the Atlantic. Some scientists have proposed that the Mediterranean Basin dried up to the point of complete dissication, but this view is un- tenable. Some predictions Optimistic predictions are frequently made about man's exploiting the sea for its "un- limited riches." Artists, uninhibited by prac- tical considerations, sketch undersea cities fre- quented by fish-men and midget submarines. Science cannot compete with such science fiction. There is a credibility gap between such brochuremanship and practical realiza- tion. Nearly a century ago Alexander Agassiz, while exploring the South Pacific, lamented that he could not even feed his own crew with the fish caught in his deep-sea 'trawl. We can hardly care for the world's excess population by housing them beneath the sea, since only the rich could afford this luxury. This would be like attempting to care for Haiti's excess people by housing them aboard luxury liners and dispatching them on an endless trip around the world. But if the sea is not a bottomless cornu- copia, it does have many assets. We should not write off the oceans, for the history of technology reveals that bizarre contempla- tions are often achieved. The land is broad, but the sea is wider. Today the frontiers of the West have passed into history, but the oceans around us remain a deep frontier. The Truman proclamation two decades ago, which added the contiguous continental shelves to the United States, added more ground than the Louisiana Purchase. With today's quickened pace of technology, the general promise of the oceans looms large. Yet it remains impossible to identify fully just what resources are to be gleaned. Legal problems of jurisdiction and owner- ship abound. But these already have been sat- isfactorily solved for the North Sea. By treaties concerning oil rights, this aqueous territory has been peacefully carved up among the several contiguous nations. We can be sure that the deep abyss, the basin into which the ancient sediments have gathered, holds many magnificant secrets. The ocean may hold the key to man's survival. We are already straining the array of traditional land resources including, curiously enough, even water. We must seek help from the sea, we must turn to the sea. ■ THE AUTHOR Dr. Robert S. Dietz teas a eodiscocerer of sea floor spreading. He is a marine geologist at NOAA Atlantic Occanograpliic and Meteorological Laboratories, Miami, Flu. He specializes in the structure and processes of tlie deep ocean floor. 806 COLLAPSING CONTINENTAL RISES: ACTUALISTIC CONCEPT OF GEOSYNCLINES-A REVIEW BY ROBERT S. DIETZ and JOHN C. HOLDEN A reprint from MODERN AND ANCIENT GEOSYNCLINAL SEDIMENTATION R. H. DOTT, JR. and ROBERT H. SHAVER, editors Society of Economic Paleontologists and Mineralogists Special Publication No. 19 1974 807 COLLAPSING CONTINENTAL RISES: ACTUALISTIC CONCEPT OF GEOSYNCLINES— A REVIEW ROBERT S. DIETZ AND JOHN C. HOLDEN NOAA, Atlantic Oceanographic & Meteorological Laboratories, Miami, Florida ABSTRACT In the 1950's, geosynclinal theory was dominated by the tectogene concept and Marshall Kay's synthesis. These and earlier concepts were derived from field study of tectonized geosynclines on land. In 1959 C. Drake, Maurice Ewing, and G. Sutton, applying the data of marine geophysics, recognized that sedimentary prisms now being laid down along the eastern margin of the United States may represent nascent miogeosynclines and eugeosynclines. They assumed that there is a close parallel with Kay's model and included in their interpretation a shelf-edge basement high that supposedly is equivalent to the tectonic borderland and, also, a toe of sialic crust underlying the continental rise that supposedly makes the rise ensialic. The eugeosyncline then would be elevated eventually to continental level largely by sialization of oceanic crust and without horizontal translation of the prism. Between 1963 and 1967, we have developed what may be called an actualistic concept of geosynclines that is based upon sea-floor spreading and collapsing continental rises. This, too, was based upon Kay's model, except that gross surgery was applied. The seaward half of the miogeosyncline was deleted, as though it never existed and making it a wedge that thickened out, so to speak, like the modern terrace wedge. Also omitted was the tectonic borderland; instead, a continental slope was inserted between the miogeocline and eugeocline. (For simplicity and since none of these sedimentary prisms are really synclinal in form, we prefer the terms miogeo- cline and eugeocline.) In this model, the miogeoclinal sediments were deposited ensialically on a downflexing continental margin and the eugeoclinal sediments ensimatically on oceanic crust. There seemed to be insufficient reason to equate the shelf-edge basement high wi;h a tectonic borderland or to insert a sialic toe beneath the continental rise. Tectonization was envisioned as the result of underthrusting of the continental margin (sub- duction), which collapsed the continental rise, magmatized it, and inserted allochthonous crust and mantle rock within the eugeocline. Our model is explicitly concerned with the mio-eugeoclinal couplet of the Atlantic type, such as would form marginal to a rift ocean on the trailing edge of a drifting continent. With the rapid development of plate tectonics and especially with the recognition of opening and closing ocean basins, much sophistication has recently been added to geosynclinal theory by J. Dewey, J. Bird, A. Mitchell, H. Reading, W. R. Dickinson, and many others. introduction to do this ourselves, we are certain that essen- t-, r it.: • * u -„A tially all authors will embrace plate tectonics I he purpose of this paper is to review briefly . ,. . , the development of actualistic geosynclinal the- and actualism. A 1c°"feren^e °n geosynclines oryi in North America between the years 1951 convened in, say, 1966 would have resulted m to 1967 as was suggested by the symposium con- ^Ulte a different set of papers in which at least vener. These dates are not arbitrary, as 1951 is some °* the authors would insist that there are a landmark year in which Marshall Kay, to "° modern-day equivalents of Paleozo.c and whom this conference is appropriately dedi- Precambr.an geosynclines. cated, published his classic monograph, North T^SPace Imitations prevent any rev.ew of pre- Am»rican Geosynclines (1951 ). A geologic rev- Kay co™?*tsn except to pay h°mage to ,Stllle s olution occurred commencing in about 1967 with (*:*■> l936> 19411 ) v,ews on orthogeosynchnes as the wholesale acceptance of what is now called hem% marg,na to cratons and comprised of a plate tectonics. This, in turn, has remarkably af- mio-eugeosynchnal coup et and, also, to Haug s fected geosynclinal theory and resulted in a (1900) correct opinion that eugeosynclmal sedi- clear acceptance of actualism based upon inter- ™e nts, were laid down in the bathyal zone al- action of subduction zones with continental though by this he referred to water a few hun- margins. The extent of this revolution probably dred rn,eters defP and not to the abyssal ocean can be assessed by reading the other papers in fl°or- FrJ0T to 1950 !t was unpopular to suppose this volume. Although lacking prior opportunity that sediments were carried beyond what was called wave base and over the edge of the conti- 1 Editor's note. The authors prefer "actualistic" to nental slope. We should also recall that one of "uniformitarian" whenever modern sea-floor phe- Schuchert's (1925) "certain facts" of geology nomena are used as analogues for interpreting ancient Was that, not only did the Paleozoic borderland rocks (R. S. Dietz, written communication, May 10, r A i i_- r a ±x. j. tt ■*. j c±. * 1973). See p. 1-2 for a discussion of the history and of Appalachia he off the eastern United States, meaning of actualism. but the continent was surrounded by seven other 14 808 COLLAPSING CONTINENTAL RISES 15 borderlands as well. We can also recall the vogue for tectogenes both as great downfolds within the craton and as features related to trenches. For these last two concepts, let it be sufficient to say, requiescat in pacem. An excel- lent summary of geosynclinal theory prior to 1950 has been provided by Glaessner and Teic- hert (1947). KAY S CONCEPT OF GEOSYNCLINES The need for brevity prevents us from re- viewing Kay's (1951) fundamental work except to reproduce his plate 9, our figure 1, which quickly became the textbook example of a mio- eugeosynclinal couplet even though it was not Kay's intent that this be so (personal communi- cation). It should be recalled that at that time *A. N. Y. VT. N. HAMP. ME. MIOGEOSYNCLINE EUGEOSYNCLINE MIO. OUTER HALF TEC. BDRLND / Fig. 1. — Kay's geosynclinal couplet. A drawing to show that, if three out of five elements are deleted from Kay's. (1951) classical example of an ensialic mio-eugeosynclinal couplet, model is transformed into an ensialic- ensimatic actualistic geosynclinal couplet. Outer half of miogeosyncline, tectonic borderland, and island arc are eliminated ; a continental slope is inserted, beyond which eugeocline is inserted. A, Mio-eugeosynclinal couplet along eastern North America palinspastically reconstructed as of mid-Ordovician when orogenesis began, according to Kay (1951) ; B, deleted elements, cut out of diagram A by scissors; C, new paste-up of mio- eugeoclinal couplet with new ensimatic eugeocline being downdropped along continental slope according to actualistic concept of geosynclines (Dietz', 1963a), by which pre-Middle Ordovician sedimentary prisms shown may be equated with sedimentary prisms along modern continental edge of eastern North America (adapted from Dietz and Sproll, 1968). 809 16 ROBERT S. DIETZ AND JOHN C. HOLDEN almost nothing was known about the ocean floor — almost nothing about its realms of sedimenta- tion, nor was it even known that the ocean crust differed from continental crust inasmuch as the seismic refraction studies of Ewing and col- leagues were just commencing. In fact, many then-extant misconceptions can now be dis- missed with a smile. Considering the state of the art, we may conclude that Kay's synthesis showed remarkable insight. He, for example, recognized the marginal position of most ortho- geosynclines and the possible construction of the continents by the accretion of geosynclinal foldbelts. On the other hand, the continental terrace sedimentary accumulations of the mod- ern east coast and Gulf Coast were regarded, not as miogeosynclines, but as a new type of geosyncline, the paraliageosyncline, having uncertain affinities with miogeosynclines. Kay was naturally unaware of the enormous sedi- mentary prisms that lay at the base of modern continental slopes. While not subscribing to the then-usual belief that all geosynclines were nec- essarily ensialic, Kay made few inferences about the nature of the crust underlying geosyn- clines. The nature of this crust, although basic to a complete understanding of geosynclines, is nowhere shown on his figures. All of Kay's eu- geosynclines were palinspastically reconstructed to lie at sea level with no indication of the posi- tion of that most important of all topographic boundaries, the continental slope. The role of turbidity currents in transporting sediments to the deep sea, so ably championed by Ph. H. Kuenen, was then only just beginning to be rec- ognized. In figure 1 we also show how we sup- pose Kay's concept, with some modification, can be adapted to our actualistic concept of geosyn- clines. MODERN ATLANTIC CONTINENTAL MARGIN AND GEOSYNCLINES The paper on continental margins and geo- synclines by Drake and others (1959) was an- other important landmark in North American geosynclinal theory. The authors attempted to equate Kay's concept and his palinspastic recon- struction of the Paleozoic Appalachian ortho- geosyncline (an inner miogeosyncline and an outer eugeosyncline) with the modern mid-Me- sozoic to Recent shelf and continental rise prisms (fig. 2). Thus, it was an actualistic ap- proach using the guiding precept that the pres- ent is the key to the past. Kay's example called for a geanticlinal barrier or tectonic borderland separating the miogeosyncline from the eugeo- syncline. Drake and others, in turn, identified by seismic methods shelf-edge basement highs along the eastern United States and cited exam- ples from other parts of the world that they supposed to be geanticlinal barriers in the sense of Kay. We doubt that on the basis of the seis- mic data available today one can argue any longer that such shelf-edge subsurface highs are typical of most shelves. In any event, as Burk (1968) has emphasized, buried shelf-edge highs may have many origins, some of which are non- tectonic (fig. 3). Drake and others (1959) then equated the continental rise prism with Kay's Appalachian eugeosyncline. They looked for evidences of volcanism within the prism, the hallmark of a eugeosyncline according to Stille, with only doubtful success. It was not recognized that an island-arc stage might appear later or that oceanic crust volcanics might be allochthonous, having been intercalated by sea-floor spreading. Nevertheless, their recognition of the continen- tal rise as a nascent eugeosynclinal foldbelt was certainly a great step forward in actualism. An interesting aspect of the continental rises of Drake and others (1959) with which we later disagreed (Dietz, 1963a) is their sialic un- derlining, termed transitional crust in the text but shown as sial rather than sima in the inter- preted seismic profiles. We suppose that this view, which appears to be optional insofar as seismic velocities are concerned, was in accord with the tenor of the times, which held that both miogeosynclinal and eugeosynclinal prisms were laid down on sialic foundations. Also, the view fitted well with the idea that sialization of the upper mantle must eventually follow in or- der that the crustal thickness beneath continen- tal rise prisms be increased to the continental thickness of about 35 km. From these begin- nings, the concept of a sialic toe extending from the continental slope into the deep sea became commonplace a decade ago, especially among scientists of the Lamont Geological Observa- tory, and is still widely held. Heezen's and oth- ers' (1959) stylized section across the Atlantic Ocean strongly emphasizes both the shelf-edge anticline and the continental rise sialic toe (fig. 4). It is noteworthy that Dewey and Bird (1970, 1971) have adapted this sialic underliner to their synthesis of geosynclines and mountain building. In their view, however, the toe is not newly formed sial ; rather, it is a remnant of continental rifting in which the pullapart was not a clean break but involved a taffylike neck- ing and thinning. Earlier Hsu (1965) relied heavily upon this sialic toe as evidence of crus- tal thinning and for the eventual disappearance of Appalachian-type sialic masses. 810 COLLAPSING CONTINENTAL RISES 17 o Ul */) I to z o t- o ID z 3 < _i z Z z o « UJ o < V (Tl rt a, ■*-» a, S< g M-4 m 0 m c ■/J o 3 u O Ul JS , rt rt a o en o C ? -n eu E V u ■^ a n a — C7 i* CD O 0 UJ •fl-O o ">•£ <-> >>o (/>•£! — t_, rt U in C rt i- ;» tu P o1" tu (»*) SS3NMDIH1 O -£ n O Om- N =2 (U ° o c I 8 | T- C 2 .23 £ 811 is ROBERT S. DIETZ AND JOHN C. HOLDEN BLOCK FAULTS ROTATIONAL FAULTS REVERSE OR THRUST FAULTS COMPRESSIONAL FOLDS ARCHING OR UPLIFT DIFFERENTIAL SUBSIDENCE REEF GROWTH VOLCANIC CONSTRUCTION PLUTONIC INTRUSION Fig. 3.— Shelf-margin ridges. Buried outer ridges discovered by seismic methods along some continental margins may have many origins, some of which are shown in this diagram from Burk (1968). Unless they de- form the miogeoclinal wedge, indicating that they were tectonically active during its deposition, these highs cannot be considered as tectonic borderlands in sense of Kay ( 1951). This pertains to those highs off the eastern United States where an undeformed Jurassic-to-Recent wedge overlaps shelf-edge buried ridge, which must, therefore, be at least as old as Jurassic. One possible explanation of the east coast ridge is that it is the outer flank of a graben associated with initial continental rifting. More likely explanation is that ridge is an Early Cretaceous shelf-ridge reef, an extension of that known from the Gulf Coast, west margin of Florida, and Bahama platform. Continental drift reconstructions reveal that eastern seaboard was then nearer equator than now (Dietz and Holden, 1970). MIOGEOSYNCLINES AND EUGEOCLINES Several years ago we (Dietz and Holden, 1966) proposed the term miogeocline as a sub- stitute word for miogeosyncline. This was partly in the interest of simplicity but, more im- portantly, to emphasize that miogeosynclines are seaward-thickening prisms of shallow-water sediments laid down mostly above surf base. Thus, miogeosynclines comprise only half of, or one limb of, a syncline. We pointed out that all folded and cratonized miogeosynclines seem to have this aspect. Further, it seemed unlikely to us that the outer limb of the miogeosyncline was lost by uplift, thrusting, and subsequent erosion, as some writers argued, in such manner that the outer limb would be lost from the geologic re- cord. With our model it was possible to equate directly ancient miogeosynclinal prisms with such modern shelf-terrace prisms as that cap- ping the coastal plain and continental shelf of the eastern United States (fig. 5). The term miogeocline now has become widely accepted, as has the companion word eugeoclim as well. We believe that this is proper, espe- cially for those uses in which the plate-tectonic concept of geosynclines is implied. Certainly, if we equate eugeoclines with the continental rise prism, the sedimentary body is wedge shaped as well, but in this event the thickening is toward the continental slope. Only when the miogeo- cline and eugeocline are placed together as a couplet is the resulting sedimentary body syncli- nal in form (fig. 1). ACTUALISTIC CONCEPT OF GEOSYNCLINES AND MOUNTAIN BUILDING In 1963 we (Dietz, 1963a) took issue with previous thoughts on the geosynclinal cycles as 812 COLLAPSING CONTINENTAL RISES 19 ttuoyjOj re — -EH (TJ.X to v CV ^ TS c c 2.^< 2 8 8 C M o re c Ih c K c re 5 u £ o C ;- ^ o MH u Cm c u 3 re 13 TO O 3 0 u u :< 'p M"0 ~ C ^ re — tB"< c u -o , . u O 3 re U, ^ .C 0 = co U re re CD < C -^ a 1 CO u o re E u > '— 3 u CO u. cu o 3) c Cm "0 "o , C Xl ^j • d-o o a O " u 3 s.S'a.l g h^ ra>x> 11 K _ rt t/i M o?3 S.S^ I s s 2- & •8 A g s o .5 -.2.2 E c oSf5.o3 2 S 5-9 "1 a S s g Ei3 § » _. § ui g "S E S fj I ^ P !" P I >! bo.S r" tj fe 03 1) to3spfc 814 COLLAPSING CONTINENTAL RISES 21 applied to the eastern margin of North Amer- ica. Utilizing Hess' (1962) concept, sea-floor spreading, translation of the ocean floor, and underthrusting (subduction) at continental margins was propo?ed as the driving mecha- nism. This was termed "an actnalistic concept of geosynclines and mountain building," and continental rise prisms were regarded as nas- cent eugeoclines. The proposed model is best ex- plained in a series of drawings (figs. 6-7), but a few words of explanation are needed as well. Sedimentation phase. — Along the trailing edge of a drifting continent like North America, a large prism of terrigenous sediments accumu- lates at the base of a continental slope and builds a continental rise. These sediments would be of the poured-in type, carried down subma- rine canyons and deposited as turbidites, or, in the broad sense, would be equivalents of flysch. As it grows, this prism, a eugeocline, slowly subsides isostatically, causing downwarping of the adjacent sialic continental margin. Prograd- ing paralic deposits build up a monoclinal wedge of shallow-water miogeoclinal deposits on this marginal flexure. Because sedimentation causes the subsidence, this entire geosynclinal develop- ment is gravitationally induced (Dietz, 1963a). We erred in 1963 in not recognizing the impor- tant role of lithospheric cooling (Sclater and Francheteau, 1970), which now appears to be an important cause of continental margin subsi- dence. From the simple dike-injection concept of sea-floor spreading, it is not immediately clear why the sialic craton should subside rather than only the ocean floor being created at a level of a few kilometers lower than the sial. Nevertheless, it appears, from the history of high Africa and from the arching of the sialic flanks of the Red Sea, that continental uplift and crustal thinning by erosion precedes conti- nental rifting and the appearance of a midocean ridge. Mantle plumes and associated so-called hot spots may be involved. However, we should not entirely set aside regional isostatic down- bowing owing to sediment loading as a compan- ion cause. A recent analysis by Walcott (1972) found this effect to be both real and important. Orogenic phase — "Orogeny is ushered in by the simatic ocean floor moving toward and underthrusting the buoyant con- tinent— presumably by the mechanism of sea-floor spreading. The eugeosyncline is compressed, folded, thrust, magmatized and metamorphosed. Ultra- basics, from the old sea floor upon which the sedi- ments were deposited, are caught up in the folding. The miogeosyncline is also affected, but to a milder extent, as it is resting on tectonically passive sial — only the sima is active. . . . The eugeosyncline is accreted to the continent and becomes an intrinsic part of it — its outer margin forms a new continental slope" (Dietz, 1963a). Late and postorogenic phase — "The sea floor continues to underthrust, so now a trench forms at the continental margin. The sea floor, including its sedimentary layers and any de- tritus poured into the trench, is mostly carried beneath the continental raft and granitized. . . . Granite batholiths invade the continental margin, adding buoyancy and causing diapiric and general uplift of alpine mountains. Eventually the sea-floor thrusting ceases and the mountains are eroded. With erosion, further isostatic uplift occurs, but eventu- ally a congealed 'and stable craton results. The stage is set once more for the sedimentation of a new con- tinental rise and eventual development of new mar- ginal orthogeosynclines" (Dietz, 1963a). It is interesting to recall that the following five views, to which many of the arguments on the actnalistic geosynclinal concept were ad- dressed, were regarded as unorthodox at the time : ( 1 ) that deep-sea sediments, even as tec- tonized metasediments, are ever found on conti- nents (permanency of continents and ocean ba- sins); (2) that large amounts of terrigenous sediments reach the deep ocean floor and that the continental rise prism is a giant, isostatically downbowed turbidite prism; (3) that fragments of the ocean crust and upper mantle appear in eugeoclines so that it was not really necessary to drill a Mohole to obtain such samples — we have been unable to discover any friend of the defunct Mohole Project for several years now; (4) that eugeoclines are generally ensimatic and only the miogeoclines are ensialic ; and (5) that miogeosynclinal sediments, prior to exogeo- synclinal deposition, were derived from the landward side and that they thicken azvay from their source. Many recent papers on geosyncli- nal theory that embrace sea-floor spreading and plate tectonics seem now to use these views as explicit or implicit premises. Some of our own thoughts on geosynclines and their associated realms of sedimentation have been developed in several papers (e.g., Dietz, 1963b, 1963c, 1964, 1966; Dietz and Holden, 1966, 1967). CONCLUDING REMARKS In this brief review, no attempt has been made to bring the subject up to date inasmuch as the geosynclinal concept is now in a state of ferment occasioned by the advent of plate tec- tonics. Excellent treatments have recently been 815 22 ROBERT S. DIETZ AND JOHN C. HOLDEN 816 COLLAPSING CONTINENTAL RISES 23 provided, for example, by Mitchell and Reading (1969), Dickinson (1970) and by Dewey and Bird (1970). This review also has been explic- itly limited to the mio-eugeoclinal couplet such as would form along the trailing edge of a drift- ing continent. In such a regime, the margin is stable and is of the Atlantic type except that the subsidence is caused by regional isostatic com- pensation owing to the load of the continental rise prism. Added to this is lithospheric subsi- dence associated with cooling as newly formed ocean crust moves away from its place of origin at the midocean rift. Of course, it takes the cre- ation of a new subduction zone to convert an opening ocean into a closing ocean. Such an event is also required to collapse a continental rise, a nascent eugeocline, into a folded eugeo- cline as a mountainous foldbelt or orogen. Let it be sufficient to say, many and varied scenarios are possible along a trench ocean of the Pacific type having margins that are being elevated and frequently subjected to transcur- rent faulting, especially where the strike-slip component of subduction is taken up, not in the trench axis, but within the arc-trench gap. For example, if the Franciscan melange is composed of collapsed trench turbidites and large admix- tures of skimmed-off oceanic crust and if the Great Valley Sequence was laid down in an arc- trench gap, these circumstances suggest a facies quite different from that resulting from the ini- tial collapse of a mature continental rise of the Atlantic type. The concept of actualistic geosynclines wherein sediments are deposited on the ocean floor and then accreted to continental margins by plate tectonics satisfactorily explains how sedi- mentary prisms are transformed into folded mountains. The close relationship between eu- geoclines and foldbelts is not one of cause and effect, but one of jeopardy of position — sedi- ments laid down on the ocean floor are returned to the continental margin by sea-floor spreading. An active continental margin is the locus of in- teraction between continents and subduction zones. Considering the complex history of geosyn- clines, one may ask, should we not scrap this term, as it only leads to confusion? This, of course, is not our decision to make, as terms will thrive or fall depending upon their usefulness in geologic communication. We suppose that the term, together with its plethora of Greek pre- fixes, will remain as a basic concept in geology but also that a new classification will develop. Most significantly, such a classification will be based upon the world today and upon the fate of sedimentary deposits laid down at continental margins within the framework of plate tecton- ics. Geologists will no longer simply attempt pa- linspastically to erect nascent geosynclines from the corpus delicti, ancient, particularly Paleo- zoic foldbelts — at least not as type examples. Rather, we will compare these tectonized depos- its to modern sedimentary prisms. This is the essence of actualism. REFERENCES Burk, C. A., 1968, Buried ridges with continental margins; New York Acad. Sci. Trans., ser. 2, v. 30, p. 397-409. Dewey, J., and'Bird, J., 1970), Mountain belts and the new global tectonics: Jour. Geophys. Research, v. 75, p. 2625-2647. , and , 1971, Origin and emplacement of ophiolite suite: Appalachian ophiolites in Newfoundland: Ibid., v. 76, p. 3179-3205. Dickinson, W. R., 1970, Plate tectonic models of geosynclines : Earth and Planetary Sci. Letters, v. 10, p. 165-174. Dietz, R. S., 1963a, Collapsing continental rises: an actualistic concept of geosynclines and mountain building: Jour. Geology, v. 71, p. 314-333. Fig. 6. — Collapsing continental rises. Miogeoclinal sediments deposited as marginal wedge on craton rather than in. intracratonic trough (i.e., behind a shelf-edge ridge). A, Initially (late Precambrian to Middle Ordovician), miogeoclinal sediments are deposited on a marginally flexing continental edge similar to that now developing on the continental shelf off eastern United States ; B, Orogeny collapses continental rise in Late Ordovician, terminating true miogeoclinal deposition and initiating flysch deposition (e.g., Martins- burg), within marginal cratonic basins or exogeosynclines ; C, continued orogeny and further subsidence of miogeocline wedge and molasse deposition ; D, Appearance as of today but with shoreline showing maximum incursion of prograding sea over coastal plain; not shown is probable collision of Africa with North America and formation of subduction zone at first in open Atlantic with an associated island followed by migration of this arc to continental margin. (From Dietz and Holden, 1966.) 817 24 ROBERT S. DIETZ AND JOHN C. HOLDEN NORTH AMERICA AFRICA ~*K CONTINENTAL SHELF CONTINENTAL slope vPROTO ATLANTIC OCEANIC CRUST APPALACHIANS \ ^ COASTAL I MID ATLANTIC RIFT Fig. 7. — Closing and reopening of Atlantic Ocean. Opening, closing, and reopening of Atlantic Ocean with accompanying formation of marginal foldbelts is depicted (modified from Dietz, 1972). In late Precambrian, North America and Africa were split apart by spreading rift, which inserts a new ocean basin, the proto- Atlantic. By process of sea-floor spreading, ancestral Atlantic Ocean opens. New oceanic crust is created as lithospheric plates move apart. Normal and reversed magnetic anomalies diagrammatical ly shown within oceanic crust. On margins of each continent, sediments produce orthogeosynclinal couplet : miogeocline on continental shelf and eugeocline of adjacent ocean floor. Ancestral (Paleozoic) Atlantic next begins to close. Lithosphere breaks, forming a new plate boundary, and a subduction zone is produced as lithosphere descends into earth's mantle and is resorbed. Consequent subduction collapses eugeocline, creating Appalachian foldbelt. Eugeocline is intruded with ascending magmas that create granodioritic plutons and andesitic volcanoes. Proto-Atlantic then fully closed. Opposing cratons, each carrying a geosynclinal couplet, are sutured together, leaving only a trans- form fault. Suture is locus of squeezed-up pods of ultramafic mantle rock. Sediments eroded -from mountainous foldbelt create deltas and fluvial deposits, that is, molasse. About 180 million years ago, present Atlantic re- opened near old suture line. Today, central North Atlantic is opening at a rate of nearly 3 cm/yr, and new marginal miogeocline-eugeocline couplets are being deposited. 818 COLLAPSING CONTINENTAL RISES 25 — , 1963b, Wave base, marine profile of equilibrium, and wave-built terraces : Geol. Soc. America Bull., v. 74, p. 971-990. — , 1963c, Alpine serpentines as oceanic rind fragments : ibid., p. 947-953. — , 1964, Origin of continental slopes : Am. Scientist, v. 52, p. 50-69. — , 1966, Passive continents, spreading ocean floors, and continental rises: Am. Jour. Sci., v. 246, p. 177- 193. — , 1972, Geosynclines, mountains and continent building : Sci. American, v. 226, p. 30-38. — , and Holden, J. C, 1966, Miogeoclines (miogeosynclines) in space and time: Jour. Geology, v. 74, pt. 1, p. 566-583. — , and , 1967, Deep sea sediments in but not on continents : Am. Assoc. Petroleum Geologists Bull., v. 50, p. 351-362. — , and , 1970, The breakup and dispersion of continents : Permian to present : Jour. Geophys. Re- search, v. 75, p. 4939-4956. and Sproll, W., 1968, Miogeoclines (miogeosynclines) in space and time: a reply: Jour. Geology, v. 76, 1, p. 113-116. Drake, C, Ewing, M., and Sutton, G., 1959, Continental margins and geosynclines : the east coast of North America, north of Cape Hatteras, in Physics and chemistry of earth : London, Pergamon Press, v. 3, p. 110-198. Glaessner, M., and Teichert, C, 1947, Geosynclines: a fundamental concept in geology: Am. Jour. Sci., v. 245, p. 465^482, 571-591. Haug, E., 1900, Les geosynclineaux et les Aires Continentales ; Soc. geol. France, v. 26, p. 617-711. Hess, H. H., 1962, History of ocean basins, in Engel, A., and others (eds.), Petrologic studies: Boulder, Colorado, Geol. Soc. America, A. F. Buddington vol., p. 599-620. Heezen, B. C, Tharp, M., and Ewing, M., 1959, The floors of the oceans : I. North Atlantic : ibid., Special Paper 65, 122 p. Plsii, K. J., 1965, Isostasy, crustal thinning, mantle changes, and the disappearance of ancient land masses : Am. Jour. Sci., v. 263, p. 97-109. Kay, M., 1951, North American geosynclines : Geol. Soc. America Mem. 48, 143 p. Leyden, R., Sheridan, R., and Ewing, M., 1972, Seismic refraction section across the equatorial Atlantic: Eos,v. 53, p. 171-173. Mitchell, A., and Reading, H., 1969, Continental margins, geosynclines and ocean floor spreading: Jour. Ge- ology, v. 77, p. 629-646. Schuchert, C, 1925, Sites and nature of North American geosynclines : Geol. Soc. America Bull., v. 34, p. 151-230. Sclater, J., and Francheteau, J., 1970, The implications of terrestrial heat flow observations on current tec- tonic and geochemical models of the crust and upper mantle: Royal Astron. Soc. Geophysics Jour., no. 20, p. 509-542. Spangler, W. B., 1950, Subsurface geology of Atlantic coastal plain; Am. Assoc. Petroleum Geologists Bull., v. 34, p. 2054-2060. Stille, H, 1936, Wege und Ergebnisse der geologisch-tectonischen Forschung : ( Kaiser- Wilhelm Gessel. Forh. Wiss. Festschr., v. 2. , 1941, Einfiihrung in den Bau Amerikas : Berlin, Bomtraeger. Walcott, R., 1972, Gravity, flexure, and the growth of sedimentary basins at a continental edge: Geol. Soc. America Bull., v. 83, p. 1845-1848. 819 IMPACT STRUCTURES FROM ERTS IMAGERY Robert S. Dietz, John McHone, NO A A Atlantic Oceanographic and Meteorological Laboratories, Miami, FL 33149 ERTS-1, Earth Resources Technology Satellite, provides an earth- covering, photo-like base, 1 : 1 ,000,000, on which known and suspected impact structures (meteorite craters and astroblemes) can be compared. Four types are revealed: bleached rings (Barringer, Lonar and Ramgarh craters); ghost rings (Gosses Bluff); concentric bull's eyes (Araguianha Dome); annular rings (Manicouagan, Lybynkyr). In addition, on glaciated shields "fossil craters" are erosionally etched out as circular lakes which cross-cut the regional tectonic fabric. Many astroblemes have a distinctive appearance on ERTS which suggests that a careful perusal of this imagery should reveal many more probable examples. For example, ERTS reveals a hemi-circular structure, six miles across, eight miles south of Chesterfield Inlet along the northeastern shore of Hudson Bay at coordinates 63° 1 1.5'N, 90°39'W. Only the western hemi-circle of the structure is above water and the central eye is marked by a semi-circular bay two miles across. It appears to be a quite likely astrobleme of the bull's eye type. In July 1974, with Brandon Barringer and Dyer Wadsworth, we made a reconnaissance of two circular lakes in Nova Scotia, viz. Lake Rossignol and Minard Bay on Lake Kejimkujik which appeared from ERTS imagery to be possible impact sites in a glaciated region. Our search for shock evidence and an impact tectonic style were entirely negative. Outcrops were excellent so we feel certain that they cannot be interpreted as astroblemes. However, in southern Nova Scotia two areas of pseudotachylite veins have been discovered by G. Muecke which conceivably could be related to impact shock from a yet unidentified site. We also examined Round Valley Lake in New Jersey as Alvin Cohen suggested that this feature had the style of known impact sites in Canada. Again we could find no evidence of shock and we determined that an island within a lake cannot be interpreted as a central uplift. This illustrates, of course, the need for ground truth. From ERTS the Nova Scotia sites seemed only "possibles" based mainly on circularity but their ready accessibility justified the field investigation. Presented here also are a series of ERTS images, Fig. 1-8, of some established or possible meteorite craters and astroblemes around the world. Dence (1972) may be consulted for further details on Manicouagan, Sudbury, Wanapetei, Clearwater Lakes, Labynkyr, and Lappajarvi. Dence, M. 1972. The nature and significance of terrestrial impact structures; 24th Inter. Geol. Congr., Sec. 15, 77-89. 329 820 Fig. 1 Labynkyr ring, 65 km across. This is a possible astrobleme in western Siberia (63° N, 143° E) with the annular geomorphic style of Manicouagan in a maturely dissected plateau region of the Verkoyansk Mountains 2,000 m high. Image is inverted, south to the north, so that shadows fall toward the observer. Scale on all images is 1 cm equals approx. 10 km (ERTS scene #1097-1204). Fig. 2 Ice-covered Manicouagan astrobleme in Quebec, Canada, on ERTS imagery, one of the earth's most striking features from near space 210 m.y. old (Triassic). Prominence of this annular ring is due largely to flooding associated with the recent creation of a reservoir. Shocked anorthosite (maskelynite) is found in the prominent central uplift (#1150-15044). 330 821 Fig. 3 Clearwater Lake West and Clearwater Lake East in central Canada on ERTS imagery. These circular structures were created by a twin impact in the Carboniferous about 285 m.y. ago (#1 156-15374). Fig. 4 Lake Wanapetei and Sudbury established astroblemes in Canada on ERTS imagery in wintertime. Lake Wanapetei, a Paleozoic impact event, is superimposed on northeast end of the barely discernable Sudbury Basin 40 km long. The latter was created by impact 1.7 b.y. ago and was squashed and tectonized by the Grenville orogeny circa 1.2 b.y. ago. (#1265-15465). 331 822 Fig. 5 &t't? "&t SMtgrafy Lapparjarvi, Finland, an established astrobleme, stands out boldly in this wintertime ERTS image. Although only rudely circular, the central island, which contains shocked melt rocks, is typical of the geomorphic style of an exhumed impact site in a glaciated terTane (#1234-09173). p V> • -.ft. ■3; ,*' <&. 3. , ,-■' ''£-•*''- "v.- HI - ■ ■'' i^jj f iw&i Fig. 6 Araguainha Dome in Mato Grosso, Brazil, nearly 40 km across, an astrobleme of the bull's-eye type. Dark ring marks, Punta Grosso shale, marks the outer central dome external to which are an annular series of grabens and horsts. The serrated white ring near the center is a series of vertically dipping "flat-irons" of Devonian Furnas sandstone, a few hundred meters high, which, in turn, enclose shocked Precambrian granite. This was immediately recog- nized by Nicholas Short of NASA as an almost certain astrobleme from ERTS imagery alone who did not know that one of us (RSD) already possessed shocked rocks from the site. (#1089-13005). 332 823 r i j?hI Fig. 7 Barringer (Meteor) Crater in Arizona, the prototype meteorite crater 1.2 km across on the Colorado Plateau on ERTS imagery. (#1283-17332). Fig. 8 Lonar Crater (left) in India, an established young meteorite cra- ter on the Deccan basalt plateau 1800 m across (#1131-04483). Ramgarh structure possible impact site in Rajas- than, India. It may be an eroded young crater or, more likely the eviscerated central uplift of an ancient astrobleme. (#1132-04524). 333 824 KAABA STONE: PRESUMABLY NOT A METEORITE Robert S. Dietz, John McHone University of Illinois, Urbana, IL Although listed in the Prior-Hey Catalogue of Meteorites as a probable meteorite, such an origin for the sacred Kaaba Stone of Mecca is unlikely. Both a nickel- iron and a stoney meteoritic nature seem ruled out by physical aspects based on visual inspection. One qualified observer, an Arabian geologist, has informed us that it appears to contain diffusion rings such as would be suggestive of an agate. A detailed letter from the Keeper of the Kaaba Stone's staff to a colleague provides much interesting religio- poetic information. It is regarded as a supernatural object ejected from heaven but there is little reason to equate this with a meteorite fall. However, "heaven" seems to be used in the sense of "paradise," hence it may not be geographically vectored toward the zenith. Only a few small broken bits of the Kaaba Stone are presently exposed. Most of the black substance seen is a natural resin cement (gum arabic?). Further information is provided by Farouk El-Baz, geologist with the Smithsonian Institution, who recently made the pilgrimage to Mecca and examined the Kaaba Stone. Based on our discussions with him it seems likely that only small pieces of that stone are evident as black bumps encased in the cementing substance. These bumps may be floating in the mistica or protuberances on a larger object out of sight. It may be, therefore, that the diffusion bands reported above apply to the mistica and not the Kaaba Stone proper. If so, we can say very little about the petrographic nature of that religious relic. 334 825 ^oATMOSflfc, r/V*ENT C* U.S. DEPARTMENT OF COMMERCE Frederick B. Dent, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator ENVIRONMENTAL RESEARCH LABORATORIES Wilmot N. Hess, Director NOAA TECHNICAL REPORT ERL 303-AOML 15 A Connected Least-Squares Adjustment of Navigation Data L.M. DORMAN J.W. LAVELLE BOULDER, COLO. July 1974 For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402 826 DISCLAIMER The Environmental Research Laboratories do not approve, recommend, or endorse any pro- prietary product or proprietary material mentioned in this publication. No reference shall be made to the Environmental Research Laboratories, or to this publication fur- nished by the Environmental Research Labora- tories, in any advertising or sales promo- tion which would indicate or imply that the Environmental Research Laboratories approve, recommend, or endorse any proprietary prod- uct or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this Environmental Research Laboratories pub- lication. 827 CONTENTS Page ABSTRACT 1 INTRODUCTION 1 SOLUTION 4 REAL DATA EXAMPLE 10 SUMMARY 14 ACKNOWLEDGMENTS 14 REFERENCES 15 APPENDIX 18 Introduction 18 Smooth Plotting Program Description 18 Display Program Description 26 Other Considerations 30 Reference 31 Program Listings 32 DRIVER 33 SMPLT 34 MERC 41 TYME 42 LINLSQ 43 PNAVC 45 DRAWER 46 DRAWL 47 PASTA 51 MERK 52 Data 53 828 A CONNECTED LEAST-SQUARES ADJUSTMENT OF NAVIGATION DATA L. M. Dorman" and J. W. Lavelle ABSTRACT An algorithm is described that will determine the position of a ship in the least-squares optimal sense, given infrequent and irregularly spaced estimates of the ship's position and information on the ship's attempted course and speed. The requirements imposed on the solution are: (1) that it be continuous; (2) that it be continuous in the first derivative except at points of ordered intentional speed and course change (e.g., eliminating fictitious discontinuities in the Eotvos correction for gravity data); and (3) that it accommodate short -period small adjustments to an overall course. These constraints, coupled with sufficient pro- cedural flexibility to allow user intervention in the ulti- mate determination of the track's parametrization , make this scheme a useful tool in geophysical navigation work. To emphasize its practical nature and ease of application, we have provided an example of the algorithm's use as well as an appendix which describes the content and use of subroutines written to automate the procedure. INTRODUCTION One of the most vexing problems encountered in the preparation of geophysical data taken at sea is the determination, with adequate accuracy, of the ship's position when a measurement is made. Because of the necessity of relying on position data sampled at irregular inter- vals and with irregular consistency, a reliable and straightforward method is needed to weigh each of the position measurements and to reduce them to a "smooth" track over the ocean surface. It is the Now at Scripps Institution of Oceanography, La Jolla, Calif. 92037 829 construction of an estimate of a ship's track, which is in some sense optimal, that this report addresses. The most accurate navigation control generally available to the scientific community in the open ocean is that from the U.S. Navy satellite navigation system (Guier, 1966) which provides fixes at irregular intervals whose average is 100 min or so. The position so determined is said to have a one-quarter-mile standard deviation. Talwani (1970) reviewed the systems available for interpolation between satellite fixes and discussed adjustment methods. The simplest and most widely used technique is to add a constant correction- velocity vector to the dead-reckoned (DR) track so that the DR position at the time of the second fix coincides with the location of that fix. This allows one to include variations of the ship's course and speed that have shorter periods than several hundreds of minutes. The drawback of this pro- cedure is that the correction velocities will be different for each fix pair so that the first derivative of the track, which in gravity data controls the Eotvos correction, will be discontinuous at the fixes — a situation which may at times be gravely unrealistic. Bowin et al. (1972) linearly interpolated the velocity between the center points of fix pairs to eliminate these discontinuities. Hayes, Talwani, and Worzel (personal communication, 1973) fitted poly- nomials to the cumulative north and east sets for single rhumb lines, obtaining a correction vector which varies smoothly with time in an effort to eliminate the unreal first-order discontinuity problem. 830 In an entirely different approach toward improved navigation, Johnson (1971) demonstrated how observed bathymetric or gravity fields in the vicinity of track crossings may be used to improve the estimates of the ship's position. Although this self -consistency approach can be valuable, the difficulties associated with automating the procedure and the dependence on the observed field will likely limit its application as a general-purpose tool. The algorithm we present may be of some help with that problem, however, as the parametrization of the correc- tions used by Johnson is similar to our own. In fact, depending on the need for additional constraints and the tractability of the observed fields , it may be possible to develop a hybrid procedure based on the inclusion of his crossing equations in our observational system. What we present here is an improved navigation method without the problem of fictitious velocity jumps. We adjust a track so that the long wavelength features of the track are controlled by the satellite (or other) navigation system while the short wavelength features are taken from the DR input. The adjustment process preserves the conti- nuity of the track (a connected track) and allows discontinuities in the velocity (and hence in the Eotvos correction) only at points of actual speed or course change. Finally, the adjustment process is flexible enough to allow user intervention in the decision as to when additional correction parameters are to be used. This later consider- ation allows the track to follow the navigation input more closely (accept shorter wavelength corrections) when fixes are frequent and reliable, but accepts only longer wavelengths when fixes are infrequent or unreliable. 831 SOLUTION In the following treatment, we will work with a DR track which is constructed using ordered or estimated courses and speeds because these are most commonly available, although a DR from log and compass can be as easily used. We are also considering the case of a ship steering a constant course (a rhumb line) over some interval of time and then turning to steer another rhumb line. This is the most common occurrence in geophysical survey work and provides us with the simplicity guaran- teed by the conformal Mercator projection, dealing with the tracks in a rectangular Cartesian coordinate system. The only disadvantages are those of a latitude -dependent scale. The core of our suggested procedure is to make use of an explicit dependence of the ship's position on time, a technique unavailable to the manual smooth plotter. In Cartesian coordinates, the east (X) and north (Y) components of the two-dimensional vector function of time describing the ship's position can be treated separately. Our problem then .becomes one of fitting two functions X(t) and Y(t) to the x- and y-components of the available fixes. To satisfy our objectives con- cerning the wavelength of the adjustments that we are willing to make, we let X(t) be the sum of the x-component of the DR track XDR(t) and let a piecewise smooth correction X(t), whose parameters we determine by using the method of least squares, make the corrected track X(t) pass as closely as possible to the fixes. The term "piecewise smooth" means having a continuous derivative except at a few points. The y-component is treated identically, so we will discuss only the x-component. 832 Before we proceed further, let us define some terms and notation which will become useful. A PR line is a track segment over which the ordered course and speed remain constant. A correction line is a track segment over which the wind^ and currents are expected to be constant or to vary slowly. It may consist of more than one DR line if only small course changes have been made, or it may be only part of a DR line if there is a sufficient number of fixes on the whole line. In short, it is a line on which a single correction velocity and acceleration are operative. A parameter is a polynomial coefficient representing a position, velocity, or acceleration correction which is active for part or all of a correction line. TB(J) is the start time of the Jth parameter. TE(J) is the end of the active time of the Jth parameter. IT(J) is the type of the Jth parameter. The Type 1 parameter (of which there is only one per data set) is the x-component of the origin of the trackline. The Type 2 parameter is a constant velocity correction acting over the time interval delimited by TB and, TE. The Type 3 parameter is a constant acceleration acting over the time inter- val delimited by TB and TE. This notation is chosen to preserve symmetry in the solution. When computing a correction at time TT, the effective time for a parameter is zero if TT < TB; it is TT-TB if TB < TT < TE; and it is TE-TB if TT > TE. In thd terminology of set theory, it is. the inter- section of the sets [0, TT] and [TB, TE]. 833 To insure the continuity of the correction vector, we let X(t) be obtained by integrating the x- components of the various correction velocities and accelerations acting since the time origin of the problem. At times of speed changes or major course changes, where the effect of the wind and seas on the ship's motion can be markedly altered, we require only continuity of position. At those times, we allow the correction velocity to change. Along a track segment where we expect the set to vary slowly, we allow flexibility in the correction by letting a new correction acceleration to be added from time to time, thus allowing curves to be added to the trackline while maintaining continuity of velocity. In the case where the fixes along a track seg- ment are insufficient to determine a correction velocity or acceleration, we can accept the DR track by simply not adding any correction veloc- ities or accelerations. The function X(t) is thus similar to the spline function in that it is piecewise polynomial; but it differs because it will generally be a least-squares approximation instead of an interpolation and because the continuity constraint is not the same at all junction points of the polynomial segments. We demonstrate how the function X(t) is constructed by using as an example a portion of a real survey. The fixes and the adjusted track- line are shown in figure 1, and the navigation input is shown in figure 2. A detailed explanation of the data input is given in the appendix. 834 The parameters of the correction function X(t) , which we must determine by our least-squares fit, are contained in the vector B that we determine by solving the matrix equation A x B = C + E . (1) This matrix equation is composed of one scalar equation for each fix in the data set. C is a vector whose i -component is the x-coordinate of the i -fix minus the x-coordinate of the DR position at the time of the fix. E is a vector of observational error and A is the matrix of coefficients which we will develop shortly. After reading in all the information comprising a set, the beginning, end, and number and types of parameter on each correction line are determined according to the following basic rules : (1) The first parameter (and the only Type 1 parameter) will always be a position (the origin of the adjusted trackline) . (2) The current correction line is terminated and a new one is begun when there is a change in ordered speed or a major (> 10°) course change. (3) Each correction line will have two new parameters, a velocity and an acceleration , except in the following circumstances : (a) If the number of fixes on a correction line is smaller than NDFA, a preset constant, the acceleration is omitted (2 < NDFA). (b) If the number of fixes on a correction line is smaller than NDFV, a preset constant, input course and speed are accepted (1 < NDFV < NDFA) . (c) New velocity or acceleration parameters can be added at any time the user desires to allow for more complicated curves in the correction. The new velocity and acceleration parameters act from their start times until the termination of the correction line to which they belong. . 835 Having determined the number, types, and start and stop times for all parameters in B, the next step is to generate the matrix A. Each row of A, when multiplied by B, must give the integrated correction distance up to the time of the fix. The integrated correction distance for the Type 1 (position) parameter is simply the parameter itself. For the Type 2 (velocity), it is the parameter multiplied by the effective time; and for the Type 3 (acceleration), it is one-half the parameter times the effective time squared. In the example (see figs. 1 and 2), the first equation repre- senting the first fix is BCD + B(2) (TT-TBC2]) + B(3) (TT-TB[3])2/2 = XFixl " XDR (TT) (2) where TT is the time of the fix. The times TB [2] and TB [3] are equal to the start time of the line . In our example , the first line has seven fixes so that the first seven equations are of this form, differing only in the value of TT and X . . Xp. • is the x-component of the DR position at the time of the i -fix. The eighth fix is on the second correction line, and its equation is 2 B(l) + BB(2) (TE[2]-TB[2]) + B(3) (TE[3]-TB[3]) I2 + B(4) (TT-TB[4]) + B(5) (TT-TB[5])2/2 = XFix8 - XDR (TT) (3) where TE[2], T£[3], TB[4], and TB[5] are the times of the first course change. The redundancy in variable names preserves a symmetry which is 836 useful in setting up the algorithm numerically. The generalization of these equations for the i -fix and M -correction line is straight- forward, although we avoid writing down an explicit expression because of the notational complexity involved. In any case, we continue as in the above equations until we have generated all the rows of A. We re- state that the coefficient of the B's represents elements in the A matrix . One will note that A is a "number of parameters" by the "number of fixes" dimensional matrix. This is the observational matrix described by Lanczos (1956). To obtain the square matrix which repre- sents the normal equations , we premultiply by A transpose [AT x A] x B = AT x C + AT x E . (4) Because the error moments vanish in a least-square solution, AT x E = 0, (5) one is left with the equation [AT x A] x B = AT x C (6) which is a nonsingular square matrix premultip lying the column matrix of unknowns B_, that is, the standard least-squares form. T We would like to make one remark about the structure of [A x A] Because a trackline must "forget" a fix that is far removed from it in time, the matrix [A x A] must be diagonally dominant, that is, have elements which diminish in size away from the diagonal. This is the 837 matrix analog of a fading memory. This is useful information to keep in mind when one deals with many days of navigational fixes. If such information is broken down into overlapping sets, one will be able to find overlapping trackline solutions with little difficulty. After the values of the correction parameters have been obtained in this manner, one may go back to equations of the form of Eqs. (2) and (3) to generate X(t), the least-squares optimal track at any time t. What we usually do is to generate a track solution at frequent inter- vals (say 5 min) and write these down as the end product of the calcu- lation. One will, of course, also find the positions of turning points, residuals of fixes from the track, and standard deviations of the corrector estimates. At the same time, we calculate the first deriv- ative of the track, and an EOtvOs correction is generated from the east- west velocity components. The adjusted track and the Eotvos corrections can then be combined with the observed data in the usual manner and can be plotted as in figure 1. REAL DATA EXAMPLE The example plotted in figure 1 treats a number of navigational problems which arose in a survey conducted in 1972 by the NOAA ship Discoverer near the Puerto Rico Trench. Measurements were begun at 0050 hr on Julian Day 100 (100/0050), which is the southernmost east- west line in the plot. We have set the algorithm constants so that two fixes are required before a velocity correction is computed and four fixes are required before an acceleration term is found. 838 Because the first line encompasses seven fixes , both velocity and acceleration corrections are calculated as well as the initial position of the ship. This last number is, of course, unique to the first line of any trackline sequence, as the initial position of subsequent lines is constrained to the end position of the previous line. Please note that there is one inflection point on this line at 100/0130 when the ship made a 3° course change. Because we are looking for the long wave- length corrections, we solve for only one set of correction parameters. At 0830, a turn to the north was made and a second line begun; at that time, only a velocity correction was required as only three fixes were taken. At 1320, the ship turned to the west to find the longitude of the next survey line and then turned north at 1415 to find the proper latitude. Because of the relatively short time to complete these manuevers , fixes are sparse on one of these segments . While this is a vexation in manual smooth plotting, our procedure tolerates this situation. We point out the following about lines of sparse data. There will be no velocity correction to the east-west line at 1320, so the length and orientation of this line are fixed by the lapsed time of the track and by the DR information. Therefore, a good approximation to the ship's course and speed should be input for this segment. This is not hard to do. We have found that an efficient way to handle this problem is to run the program with log speed entered as the first speed approxi- mation. On lines that have more than the minimum number (NDFV) of fixes for determination of a velocity correction, the output will suggest how 839 the log speed is likely modified in the face of prevailing current. This suggested correction to log speeds provides information for a better approximation of actual speed for weakly determined lines. The itera- tive second run through the procedure with the updated speeds provides a good estimate to the actual track. At 1615, the ship turned west to begin reflection profiling, but, as a result of hardware problems re- sulting in a poor record, was forced into retracing its course back to and beyond the start point. While the retracing allowed time to solve the hardware problems, the repositioning resulted in two short track- lines, one of which was poorly determined by satellite information. That line again is fixed in length and direction, but may translate in a way such that the overall sum of squares of residuals is minimum. At 1915, with survey hardware operational, the • ship proceeded for a period of 18 hr. Reading figure 2, one will note that small course corrections were made frequently (denoted by arrows in fig. 1) , but it is not until 101/1300 that a course change of sufficient magni- tude was made to terminate the ongoing correctors . In this case , with- out intervention, the entire line from 100/1915 to 101/1300 would have been fitted with a single velocity and a single acceleration parameter. This was judged to be insufficient in view of the apparent nonconstant and appreciable current along the track. For this reason, new acceler- ation parameters were introduced at 101/0240 and at 101/0700 to in- crease "the flexibility of the fit. These interventions show as NA cards in figure 2. One will note that the number of fixes between the NA's and between the NA's and the end of the line is at least equal to NDFA (in this case, four). 840 As an aside, one should also note that this line is parallel to the east-west line below it, although they were run 24 hr apart. In addition, the two longest north-south lines exhibit a parallelism, all of which suggests the occurrence of a localized current running to the southwest . At 1550, this east-west line was complete, and the ship slowed to bring in some of the streamed gear as the ship turned to the north- east to begin a quick run to the next survey line. Because of the large accelerations and decelerations at both ends of this line, we have decoupled this section of track from both the previous and following track solutions. This is evident as a gap in the line in figure 1. At 101/1910, we began another line. We spare the reader detailed description of the line, which may be easily assembled from figures 1 and 2. Many features of the above description reappear on this track, suggesting that such navigational data are typical of a real survey and can be handled by the procedure. As we have mentioned before, the memory of previous fixes retained by any line fades as the point of interest in time moves away from those fixes . This means that there is no real limitation to the number of tracks that the procedure will handle. If one has more fixes than can be handled by the available computer, then one may break the data into overlapping sets with the assurance that if the overlap were great enough, one would be able to find solutions that blend together in some region. 841 SUMMARY We have suggested and demonstrated the usefulness of an algo- rithm which absorbs position measurements and ordered courses and speeds and calculates a connected smooth plot of the track. This procedure is based on quadradic-connected least-squares approximations for both latitude and longitude fixes explicitly parametrized by time. The resulting calculated track is continuous and assures one of continuous first derivatives (and hence Eotvos corrections), except at points of real speed or course change. Computer subroutines based on this algo- rithm and a description of their use are presented in the appendix. Because of the incompatibility of precise geophysical measurements and poor navigation, we think this procedure may contribute significantly to geophysical measurements taken at sea. ACKNOWLEDGMENTS We thank Stuart M. Smith for critically reading the manuscript. This work was funded in part by the National Science Foundation-IDOE Grant AG-253. 842 REFERENCES Bowin, C. , T.C. Aldrich, and R.A. Folinsbee (1972): VSA gravity meter system: tests and recent developments, J. Geophys. Res. 77:2018- 2033. Guier, W.H. (1966): Satellite navigation using integral Doppler data — the AN/SRN-9 equipment, J. Geophys. Res. 71:5903-5910. Johnson, R.H. (1971): Reduction of discrepancies at crossing points in geophysical surveys, J. Geophys. Res. 7£: 4 892-4896. Lanczos , C. (1956): Applied Analysis^ Prentice Hall Inc., Englewood Cliffs, N.J., 539 pp. Talwani, M. (1970): Developments in navigation and measurement of gravity at sea, Geoexplovation 5:151-183. 843 82619 o ro e 00 ID O ro e (T> m o o o O <0 o ro o O <£> Z o o o 00 o ro e "8 o rO e CD 1 CO CD ?H SL, g -^ 3 •^ CO CO o tO cd CO Alti^ CO V CD t-^ « ^ !n ^ Sh O -^ a +i CO O CO « ^ • 0) v-£ •"W ^ co CO K co •ri Cj (» O r-g S^ ?H 3 S S co O <3i +i •^ V ^3 « -^ <+-, £ « Cj CO +^ £ +i O V *> g £ co •^ S13^ O « co « a. HJ> ^ CO CO Sh CD 5 -^ w -(^ •^ ^ -|^ « -U> £ Co CO V •«i rSi •** "tt +i £ s V K -^ •^ 3 O £ V I CO ^+iQ 3 -v CjtO O CO £ is co In o ?H t-i C} 4i « CO ^ S ?s S -^ T~~i V V 1^1 CO A? « 4J> CO s s s « CO cd cu ?h Cij.S 4i CD o H ^ ^— CO Eh «■« CO . +i Q) p • H ^ "O co •*S 4i r£ «K S £ s ova; « CO CO •^ CD 4^> 3 « \~-i ?H o ^ 3 CD ^ g +i ^ 3 CL, CD r« CD tj CO ^ 4^> rg CD K 4^ a; o s !n •<5 • O K « ■p r-S O g CO ■ts CD CD CD CO CD ?H Sh Co CD » s s a ^ ^ o Cjj^Q CO CO •ti &4 844 DAY TIME LATITUDE LONGITUDE COURSE SPEED TYPE DAY TIME LATITUDE LONGITUDE COURSE SPEED TYPE 100 0050 094 5 TP 101 2314 17 339 -60 040 176 5 SA 100 0100 16 336 -59 091 091* 5 SA 102 0000 180 5 TP 100 0130 097 5 TP 102 0056 17 241 -60 038 180 5 SA 100 OIM 16 339 -59 052 097 5 SA 102 0152 17 188 -60 037 180 5 SA 100 021*6 16 338 -58 598 097 5 SA 102 0240 180 5 NA 100 0330 16 337 -58 560 097 5 SA 102 0240 17 11.2 -60 037 180 5 SA 100 0606 16 333 -58 1*23 097 5 SA 102 0338 17 081. -60 04 1 180 5 SA 100 0706 16 330 -58 371 097 5 SA 102 0530 16 575 -60 057 180 5 SA 100 0752 16 327 -58 332 097 5 SA 102 0600 177 5 TP 100 0830 002 5 TP 102 0718 16 471 -60 078 177 5 SA 100 0902 16 350 -58 297 002 5 SA 102 0756 16 432 -60 084 177 5 SA 100 1052 16 1*56 -58 299 002 5 SA 102 0830 090 5 TP 100 1244 16 562 -58 296 002 5 SA 102 0912 16 393 -60 070 090 5 SA 100 1320 270 61 TP 102 1104 16 393 -59 586 090 5 SA 100 1334 16 597 -58 309 270 61 SA 102 1242 16 386 -59 520 090 5 SA 100 1415 004 55 TP 102 1338 16 381 -59 477 090 5 SA 100 1432 17 009 -58 351 001. 55 SA 102 1426 16 382 -59 438 090 5 SA 100 15H 17 01*9 -58 353 004 55 SA 102 1440 08 3 5 SA 100 161 5 269 55 TP 102 1524 16 386 -59 394 083 5 SA 100 16l»0 17 113 -58 380 269 55 SA 102 1616 16 1*08 -59 339 083 5 SA 100 1715 090 5 TP 102 1654 16 403 -59 307 O83 5 SA 100 1752 17 1 1 1 -58 397 090 5 SA 102 1730 086 5 TP 100 1830 17 113 -58 362 090 5 SA 102 1730 086 5 NA 100 1915 270 5 TP 102 1756 16 1756 -59 247 086 5 SA 100 1936 17 109 -58 337 270 5 SA 102 1842 16 427 -59 204 086 5 SA 100 2018 17 109 -58 385 270 5 SA 102 1915 090 5 TP 100 2100 268 5 TP 102 1940 16 428 -59 141 090 5 SA 100 2214 17 119 -58 509 268 5 SA 102 2030 16 428 -59 094 090 5 SA 100 2230 266 5 TP 102 2042 16 430 -59 081 090 5 SA 101 0156 17 125 -59 134 266 5 SA 102 2215 094 5 TP 101 0240 266 5 NA 102 2224 16 437 -58 581 094 5 SA 101 0240 17 124 -59 178 266 5 SA 103 0106 16 431 -58 426 094 5 SA 101 0336 17 122 -59 238 266 5 SA 103 0115 311 16 TP 101 0428 17 118 -59 292 266 5 SA 103 0250 16 585 -58 599 311 16 SA 101 0616 17 096 -59 397 266 5 SA 103 0334 17 061 -59 085 311 16 SA 101 0700 266 5 NA 103 0438 17 172 -59 210 311 16 SA 101 0700 17 005 -59 4m 266 5 SA 103 0522 17 238 -59 303 311 16 SA 101 0730 273 5 TP 103 0545 180 5 TP 101 0804 17 075 -59 515 273 5 SA 103 0628 17 234 -59 348 180 5 SA 101 0848 17 067 -59 560 273 5 SA 103 0818 17 119 -59 355 180 5 SA 101 0915 277 5 TP 103 0830 177 5 TP 101 1000 17 071 -60 039 277 5 SA 103 0854 17 069 -59 357 177 5 SA 101 1251 282 5 TP 103 1010 16 591 -59 363 177 5 SA 101 1300 292 5 TP 103 1130 092 5 TP 101 1320 270 5 TP 103 1256 16 512 -59 284 092 5 SA 101 1332 17 108 -60 257 270 5 SA 103 1328 16 507 -59 251 092 5 SA 101 1428 17 115 -60 311 270 5 SA 103 1436 16 507 -59 186 092 5 SA 101 1518 17 124 -60 351 270 5 SA 103 1516 16 506 -59 145 092 5 SA 101 1550 103 1626 16 507 -59 079 092 5 SA 99999999 103 1645 179 6 TP 101 1550 038 16 TP 103 1725 000 65 TP 101 1614 17 174 -60 351 038 16 SA 103 '752 16 490 -59 065 000 65 SA 101 1740 17 357 -60 215 038 16 SA 103 1815 179 5 TP 101 1846 17 489 -60 113 038 16 SA 103 1848 16 510 -59 060 179 5 SA 101 1910 103 1940 16 455 -59 060 179 5 SA 99999999 103 2040 16 394 -59 067 179 5 SA 101 1910 090 6 TP 103 2134 16 333 -59 069 179 5 SA 101 1928 17 5:3<> -60 05*1 090 6 SA 103 2145 101 1940 180 5 TP 9999999 101 2124 17 441 -60 034 180 5 SA 9999999 101 2230 176 5 TP Figure 2. A listing of information input into the automated version of the algorithm that resulted in a generation of optimal track. The plot is shown in figure 1. The two -character designators have the meanings: satellite fix (SA); turning point (TP) ; and new acceleration parameter (NA) . Cards of nine separating solution sets are presented. A detailed discussion is provided in the appendix. 845 APPENDIX Introduction This appendix is designed not only to aid an individual wishing to use the programs written to implement the algorithm, but also to provide further insight into the way in which the solution was set up so that the user can extract the best solution from his data. We provide two subroutines: SMPLT and DRAWL. The subroutine SMPLT reads in navigation fixes , as in figure 2 , and calculates a best- estimate dead-reckoned (DR) track from the ordered courses and speeds. It does this by computing the correction parameter vector B for both the x- and y-components of the ship's position vector and then by generating adjusted positions interspersed with the original fixes on an output file having the same format as the input file. The subroutine DRAWL will read the output file of SMPLT and produce a set of charts showing the adjusted track and the fixes used in the adjustment, as in figure 1. The subroutines are written in FORTRAN, as defined by the American National Standards Institute (Standard X3.9 — 1966), to make them as machine -independent as possible. Those included have been run on the Uhivac 1108 and CDC 6600 computers. Nonstandard versions which run on IBM 1130 and IBM 1800 are available. Smooth Plotting Program Description This routine, the core of the solution deck, is called into operation as SMPLT (IDT, LUF, LCP, LCR, LLP, NDFV, NDFA) . These calling arguments have the following meaning: 846 IDT Time interval , in minutes , at which points on the smoothed track - line are generated. For example, in IDT = 5, positions are generated at 5-min intervals and written onto the navigation output file. LUF The logical unit designation of the scratch file upon which the fixes are written. Eight words are written on this file for every fix in a data set. LCP The logical unit designation of the navigation output file (card punch) . LCR The logical unit designation of the input file (card reader). LLP The logical unit designation of the print file upon which is written the input data, the summary of corrections, and the residuals (line printer). NDFV The number of fixes required on a correction line before solving for a constant correction velocity. If there are fewer than NDFV- fixes on a correction line, the ordered course and speed as read from the input file are accepted for that line, and only the position of the line is allowed to change. NDFA The number of fixes required on a correction line before an acceleration parameter is added to the solution for that line. This routine requires a data deck which, aside from spacers and end cards, is formatted (IX, 13, F2.0, F3.1, 2X, F3.0, IX, F4.2, IX, F4.0, IX, F4.2, IX, F4.1, 2X, F3.1, IX, A2 , IX, F6.2) with decimal points implied. This will hereafter be described as the Marine Geology 847 £ Geophysics (MG&G) Standard Navigation Format. The fields of this card, an example of which is seen in figure 2, have the following defi- nitions : Day (13): contains the Julian Date (JD) Time (F2.0, F3.1): contains the Greenwich Mean Time in hours and in minutes to tenths of minutes. Latitude (F3.0, IX, F4.2) and Longitude (F4.0, IX, F4.2): are fix latitude and longitude in degrees and in minutes to hundredths of minutes. The sign convention used is that North latitude and East longitude are positive. Course (F4.1): is the ordered or estimated course, in degrees to tenths of a degree, measured east from north. Speed (F3.1): is the ordered or estimated speed, in knots to tenths of a knot. Type of fix (A2): is a two-character symbol denoting the type of fix; or, if the card does not represent a fix, other control infor- mation as described below. Eotvos correction ( F6 . 2 ) : is the correction , in milligals to hundredths of a milligal, to be applied to gravity observations made on a moving platform. This member is not read off the input cards , but is generated within the subroutine and written on the output card images. The data deck formatted in this way consists of two types of cards: fix and control. The fix cards must bear the time of fix, the latitude and longitude, an estimated course and speed, and a designator describing the type of fix. Recognized fix labels are: satellite (SA); 848 Loran A (LA); Loran C (LC); and Omega (OM). These designators are used in a relative weighting of the fixes. Weighting is vested in a data statement within SMPLT and is now set uniformly to one. Control cards, that is, cards not bearing fix information, are of several types. The first and last cards of a connected track segment are special cards : the first card bears the time of the start of the line as well as ordered course and speed; and the last card of the same set bears only the time of line termination. A second type of control, card is that marking the turning points. In actuality, this type of card is needed only when a turning point and a fix are noncoincident in time. - The subroutine sets new correction parameters upon recognition of new speeds or course changes greater than 10° in the input stream. We denote points of velocity change that are not fixes with a TP (turning point), and the record carries only time, course, and speed. Should the latitude or longitude columns bear infor- mation, the record will be treated as a fix. The third possible control card bears only time, course, speed, and NS or NA. The difference between this and the TP control card is solely in the designator. These control cards force a new correction parameter to become active (either new velocity or new acceleration) in the calculation, although the overall course has not been altered. By using only NA cards, one guarantees velocity continuity. These cards can be used to increase the degree of fit by providing additional flexi- bility for the trackline. 849 In summary, the following rules must be observed in setting up the data deck: (1) All fix and control cards must contain a day and time. (2) Latitude and longitude fields are nonzero only if the card represents a fix. (3) New speeds and changes of course greater than 10° signal a new set of correction parameters into operation. (4) NA and NS cards can be used to increase the number of param- eters otherwise determined internally. (5) The last card of a data set contains information in the time column only. (6) Speeds and courses on sparse track segments, where sparse means the number of fixes is less than NDFV, are accepted at face value and fix the length and angular orientation of that track segment. Subroutine SMPLT has both print and type output. The tape out- put consists of information written in the Standard Navigation MGSG Format , containing every fix read in plus all calculated positions that are designated with a DR. The designators TP, NS, or NA will not appear, although the two-character UP is possible, meaning a break in the track- line. All other information on an UP record is meaningless. Printed output consists of: an input card list; a summary of correction parameters (i.e. , their magnitudes and directions as well as their standard deviations); and lastly, a listing of all" fixes and their residuals from the calculated position north and east. This summary is repeated for every solution set. 850 SUBROUTINE SMPLT c w*" ~y <=> READ DATA CARD SET NCC = FALSE READ CONSTANTS ( RETURN V INITIAIIZE NEW CORRECTION LINE <•> SET CAL=TRUE READ FIRST CARD OF SOLUTION SET IS DATE > 400 INITIALIZE NEW SOLUTION SIT -® FIX ON THIS CARD <») WRITE FIX ON SCRATCH FILE SPD CHANOE SET NCCMRUE 851 NO SOLUTION PARAMETERS FOR PREVIOUS LINE SET UPV ONLY SOLUTION FOR PREVIOUS LINE SET UP V AND 'A' SOLUTION FOR PREVIOUS LINE 852 © NO YES SH END TIMES OF NEW PARAMETERS 0 CAl INCREMENT CORRECTION LINE COUNT RESET REFERENCE COURSE AND SPEED FINISH BOOK KEEPING FOR THIS SOLUTION SH ESTIMATE LATITUDE AT START OF EACH DR LINE COMPUTE POSITIONS OF REOINNINOS OF DR LINES SET UP OBSERVATIONAL EQUATION FOR EACH FIX /WRITE POSITIONS OF/ ADJUSTED TRACK ALONO WITH FIX POSITIONS SOLVE SYSTEMS OF EQUATIONS SET CAl se FALSE SUBTRACT DR POSITIONS FROM FIX POSITIONS PRINT INPUT COURSES AND SPEEDS PRINT CORRECTION , V AND 'A* PARAMETERS P3INT FIXES AND RESIDUALS 853 A complete indexed listing of the subroutine is provided herein. A detailed flow chart will guide the interested programer through the bookkeeping maze integral to SMPLT. Display Program Description This display program, designed to allow visual integration of the data and solution, is called into operation as DRAWL (ALAT, ALONG, NX, NY, A, IDELT, NIN, NOUT, NSCAT, NPLOT) where: ALAT One-dimensional arrays representing the limiting latitudes ALONG and longitudes of a sequence of Mercator plots requisite to the display of a trackline and navigation fixes over a given area. The content of each array must be arranged in ascend- ing sequence (west of Greenwich negative) and must represent whole or one-half degrees only in decimal degrees. NX Dimension of ALAT and ALONG, respectively. Each integer must NY be between two and ten. A Plot scale in inches/degree of longitude. IDELT Time increment in minutes at which time ticks will be made (the routine checks the input file for integral multiples of this unit ) . NIN The logical unit designation of the input file. This ^BCD- coded file will correspond to the output file (LCP) of the subroutine SMPLT. NOUT The logical unit designation of the printed output file. 854 NSCAT The logical unit description of a scratch file. NPLOT The logical unit designation of the plot tape file. This subroutine allows one to plot both fixes as well as the trackline, as in figure 1, on a sequence of Mercator charts which, when manually spliced, serve to describe an area of any size at any- scale. Capability to cross the trackline at set time intervals is also provided. The routine requires only a delineation of latitude and longitude map bounds and an input file (generally the output file of SMPLT), con- taining a time-ordered sequence of points defined by a time, a position, and a two-character descriptor of the point's genesis. The input file is BCD-coded in the MGSG Standard Navigation Format which has been described above. The two-character descriptor may be one of the following: a point lying on a trackline (DR); a satellite fix (SA); an Omega fix (OM); a Loran A fix (LA); a Loran C fix (LC) ; and a break in the track- line (UP). When the DR is identified in the input file, a check is made to see if the accompanying time is a multiple of the time-tick incre- ment, allowing the DR line to be crossmarked. All other designators, aside from the UP, will be plotted with an appropriate symbol. Adjust- ments to the list of recognized fixes can be accomplished with minor changes to data statements. The subroutine will sequentially plot up to 81 Mercator charts of a contiguous area. Control of the plot boundaries is maintained through calling parameters, and a sorting of points and trackline to individual charts is done efficiently within the routine. Graticules, 855 SUBROUTINE DRAWL WliTi FIX ON TAPE WITH IC=4 (PEN UP) G> START: ENTER WITH PAIAMETEI LIST IC s 31 DEFAULT CONVERT MAP SOUNDS TO RADIANS AND MERCATOR COORDINATES COMPARE MAP SOUNDS TO PIOT SIZE IZXA * IZX IZTA « IZT WRITE FIX ON SCRATCH TAPE 856 857 chart labeling, and plot-drift indicators are drawn for each chart. The plot -tape output is initialized and terminated within the subroutine. Control of this aspect can be recovered by the programer by deactivating statements DRW 130Q and DRW 2260. Output consists of a CalComp command tape which will create a diagram, as in figure 1, as well as a printed output review of the sub- routine argument assignments. A complete indexed listing of the sub- routine is provided herein as well as a detailed flow chart. Other Considerations A complete listing of all nonstandard subroutines, called by SMPLT and DRAWL, has been provided. Comment cards in each subroutine describe their function as well as the meanings of the calling arguments. In addition to the listed routines , calls are made to two IBM standard matrix-manipulative routines, MINV and GMPRD (IBM, 1970), as well as to three CalComp standard routines, PLOT, SYMBOL, and NUMBER. Also included in the listings are two driver programs, called DRI and DRA, ch will indicate the way we have employed SMPLT and DRAWL. We have rui each separately because of the insufficient core available in our general-use computer. The user may wish to follow this example or create a single overall driver program if a larger machine is available . Notation used in SMPLT is identical to that used in the descrip- tion of the algorithm. That fact, along with the accompanying flow 858 chart, should provide the interested reader with sufficient material to guide him through the program's internal intricacies. The flow chart and previous description of DRAWL should provide the same service. We believe that we have developed a useful tool for geophysical navigation work. We therefore hope that these descriptions will pro- vide sufficient insight into the machinery of the automated algorithm that the reader will be able to make as much use of the routines as we think they merit. Reference IBM (1970): System/260 Scientific Subroutine Package Programmer's Manual, IBM Corp., Technical Publications Dept. 859 Program Listings 860 DATA LCR/5/ RFAO ,2F6.1,1 74 FORMAT! 10F 12. 2) 75 FORMAT (10112) 76 FORMAT (////////// 50X,12HNORMAL EXIT.) 77 FORMAT ( 10E12.3) 701 FORMAT < 1H1 ,48X,2AHINPUT COURSES AND SPEEDS,/, 12HT0, 7X,6HC0URSE, AX , 5HSP EED, / , 1H ,37X,2(13 2 7HDCGREES, 3X,5HKNOTS ) 702 FORMAT ( 3 6X , 2 ( 1 3 , F6 .2 , AX ) , 2( AX , F 5 . 1 , 5X ) ) 703 FORMAT ( / / // 30X , A7HC0RR EC T IONS APPLIED TO INPUT 1 /1HO,36X,AHFROM,9X,2HTO,A1X,AHSTD./32X,2( 13HD 2 5HN11RTH, 1AX, AH EAST, 5X,AH0E V. ) 70A FORMAT ( 33X , 2 ( I 3 , F6 .2 , A X ) , 2( F5 . 2 , 6H KNOTS, AA, 3 705 FORMAT ( /// /50X , 1 5HC0NTR0L SUMMARY// 1 X ,6AH LIN 1TUDE LONGITUDE ADJUSTMENT MADE TYPE /19X, 2 E NAUTICAL MILES FIX / A3X, 1 3HN0RTH E 706 FORMAT ( I A, I 7 , F6 . 2 , 2X , 2 F 10 .3 , 2F8 . 2 , 6X , A2 ) 707 FORMAT (10X,A0HTHE DETERMINANT OF THE NORMAL M 709 FORMAT (■// 10X, 56HSMPLTR WAS CALLED WITH THE FO ♦RATION /10X,5HINPUT, 15X, IA/lOX, 7HSCRATCH, 1 3X , *N OUTPUT, 3X, IA./10X, 12HPRINT OUTPUT , 8X , I A , // 1 ♦QUIRED ON A CORRECTION LINE BEFORE A VELOCITY ♦ / 10X,I2,81H FIXES REQUIRED ON A CORRECTION L ♦RATION SOLUTION IS ALLOWED. //10X, A5HSM00THED ♦0 BE GENERATED AT.IA.17H MINUTE INTERVALS //// 708 FORMAT( 1H1) WRITE (LLP, 709) LCR ,LUF , LCP, LLP, NDFV ,NDFA , I DT DDR=FLOAT( IDTJ/60.0 CALL MERC ( 30. ,-80. ,8 .0 ,0.0, 1 ) 9 CONTINUE WRITE(LLP,708) CAL=. FALSE. OFFSET*. FALSE. C SET UP NEW SOLUTION REWIND LUF NEQ=0 DO 10 1=1, NCA 00 10 J=1,NRA ) SMP 10 smp 20 500) ,C(500) ,CS( 50) , SMP. 30 (60)iSP(50), SMP AO ) SMP 50 SMP 60 S/ SMP 7 0 SMP 80 O.+EPS SMP 90 NERATED POSITIONS SMP 100 3 3 3/ SMP 110 SMP 120 SMP 130 SMP 1A0 SMP 150 SMP 1 60 EED IN KNOTS, LATITUDE SMP 17;: SMP 1 8 0 *RAD) + .000AlA9;:P2tP2SMP 190 X,FA.O, IX, FA. 2, IX, SMP 200 SMP 210 SMP 220 X,A2) SMP 230 SMP 2A0 SMP 250 SMI' 260 SMP 270 1H0,4 1X,4HFRPM, 9X,SMP 280 HDAY TIME ),3X, SMP 290 SMP 300 SMP 310 COURSES AND SPEEDS S ."•'.:> 320 AY TIME ),6X, SMP 330 SMP 3 = 1 READ (LCR»71)FD,FH,FM, FAD, F AM , FOD , FOM , CSE , SPD, IFX IF (FO .GT. 400.) GO TO 9999 CSF=CSE*:-=SPD RCSE=CSE RSPD=SPD C SET OP tJEW LIME 13 NF IX =0 C READ A CARD 14 READ(LCR»71 ) FD ,F H, FM, FAD, F AN , FOD , FOM , CSE , SPD, IFX WRITE (LLP, 73) FD , FH , F M, FAD , F AM , FDD , FOM , CSr. , SPD , I FX IF (FD . LT. 400. ) GO TO 141 CAL=.TRUE. GO TO 50 141 TT-T1ME(FD,FH,FM) CSE=CSE*RAD FA=ANG(FAD,FAM) FO=ANG(FOD,FOM) IF ( IFX .EO. NS ) GO TO 50 IF ( IFX .EQ. NA) GO TO 50 IF(FA.EQ.O.O.AND.FO.EQ.O.O) GQ TO 15 NE0=NEQ+1 NF IX = NF IX + 1 WRITE(LUF)TT,FA,FO,CSE, SPD , 1 FX ,NEQ , LN 15 IF ( ( (SPD-RSPD)^*2+(CSE-RCSE)**2) .LT. NCC = . FALSE. IF (SPD .NE. RSPD) NCC=.TROE. 17 CONTINUE LN=LN+1 T(LN)=TT CS(LN)=CSE SP(LN)=SPD IF *COS(RCSE)+SIN(CSE)-SIN(RCSE) RCSE=CSE RSPD=SPD IF ( DA .LT. .985) GO TO 50 EPS) GO TO 14 SMP 61C SMP 62 0 SMP 630 SMP 64 0 SMP 65n SMP 660 SMP 670 SMP 68 0 SMP 69( SMP 70' SMP 7 1 0 SMP 72'' SMP 730 SMP 740 SMP 75: SMP 76C. SMP 77 0 SMP 760 SMP 790 SMP coo SMP 810 SMP 8 20 SMP 830 SMP 84 0 SMP 6 50. SMP 860 SMP 870 SMP 880 SMP e9 0 SMP 900 SMP 910 SMP 92T SMP 930 SMP 9 4(.> SMP 950 SMP 960 SMP 970 SMP 980 SMP 990 SMP 100 0 SMP 1010 SMP 1020 SMP 1030 SMP 104(1 SMP 1050 SMP 1060 SMP 1070 SMP loeo SMP 1090 SMP 1100 SMP 1110 SMP 112C SMP 1130 SMP 1140 SMP 1150 SMP 1160 SMP 1170 SMP 1180 SMP 1190 SMP 1200 863 GO TO 14 C Sf:T UP NEW CORRECTION COURSE 50 WRITE (LLP, 72) NF IX ,TT IF (.NOT. OFFSET) GO TO 52 IF (IFX.FO. N A J GO TO 5 6 OFFSEl=. FALSE. GO TO 81 52 CONTINUE IF INFIX .GE. NDFA) GO TO 51 IF (NF1X .GE. NDFV) GO TO 55 GO TO 70 '' C V AND A SOLUTION 51 10=3 TB( IXB)=1R TB( IXB+ 1 )-1R TR = TT IT( IXB)=2 IT( IXB+1)=3 IXB=IXB+2 GO TO 60 C V ONLY SOLUTION 55 10=2 TBI IXB)=TP. TR = TT IT! IXB)=2 1XB=IXB+1 GO TO 60 70 10=1 C NO SOLUTION PARAMETERS ON THIS LINE Tk = TT GO TO 6 0 C A ONLY SOLUTION 56 IF (OFFSET) GO TO 57 OFFSCT=.TRUE. 57 IT ( IXB)=3 TB( IXB) = TT 1XB=IXB+1 GO TO 81 60 IF (IFX ,EQ. NA) GO TO 56 81 IF ( IFX .EQ. NA) GO TO 83 00 82 J = 2, 1XB IFlTE(J-l) .EO. 0.0) TE(J-1)=TT 82 CONT INUE 83 CONTINUE IF (CAD GO TO 100 L=L + 1 IF ( IFX .EQ. NA) GO TO 13 RCSE=CSE R$PD=SPD TR = TT GO TO 13 100 CONTINUE CALCULATE SOLUTION NPAR=IXB-1 NMX=NEQ NLN=LN C ESTIMATE LAT AT BEGINNING PF EACH OR LINE BY LINEAR INTERPOLATION IN C FIX LATITUOES NEQ = 0 REWIND LUF SMP 1210 SMP 122 0 SMP 12 30 SMP 124 0 SMP 125C SMP 1260 SUP 127T) SMP 12R0 SMP 1290 SMP 1300 SMP 1310 SMP 1320 SMP 1330 SMP 1340 SMP 1350 SMP 1360 SMP 1370 SMP 13P0 SMP 1390 SMP 1400 SMP 1410 SMP 142C SMP 1430 SMP 1440 SMP 1450 SMP 1460 SMP 1470 SMP 1480 SMP 1490 SMP 1500 SMP 151C SMP 1520 SMP 1530 SMP 1540 SMP 1550 SMP 1560 SMP 1570 SMP 1580 SMP 1590 SMP 1600 SMP 1610 SMP 1620 SMP 1630 SMP 1640 SMP 1650 SMP 1660 SMP 1670 SMP 1680 SMP 1690 SMP 1700 SMP 1710 SMP 1720 SMP 1730 SMP 174~0 SMP 1750 SMP 1760 SMP 1770 SMP 1780 SMP 1790 SMP 1800 864 •OR. NFO .EO. NMX) GO TO 510 T2=0. F2 = 0. DO 510 1=1, NLN 505 IF (T(I) .LE. T2 T1=T2 F1=F2 READ (LUF) T2,F2,FO,CSE,SPD, 1FX,NEQ,1X GO TO 505 510 FLA< I >=F1+(F2-F1 )*(T ( I )-T 1 ) / ( T2-T 1 ; COMPUTE POSITIONS FOR BEGINNINGS OF EACH OR LINE AX( 1 )=0.0 AY( 11=0.0 00 150 1=2, NLN 11=1-1 TT=(J( I )-T( 11 ) )*FAC*SP< I1)/C0S(FLA( 1 1 )*RAD) AX( I ) = AX( I l)+TT*SIN(CS( I 1 ) ) AY(I )=AY( I1)+TT*C0S(CS< 11 ) ) 150 CO NT INUE C PRINT 74, (CS( I ),SP( I), 1=1, NLN) C PRINT 74, (AX( i ) ,AY( I ), 1=1, NLN) C PRINT 74, (TS( I ),Tfc( I ) ,1 =1,NPAR) C PRINT 74, (T( I ) , 1=1, NLN) C PRINT 74, (FLAi I ) ,1 = 1, NLN) REWIND LUF 101 102 103 104 110 215 DO 200 J=1,NMX READ(LUF)TT,FA,FO,CSE,SPD, IFX,NEO,LN WRITE OBSERVATIONAL EQUATIONS FOR FIX ASSIGN WE I GMT TO F I X W(.NE0) = 1.0 DO 215 1=1,NPAR IS=IT(I) GO TO < 101, 102, 102), IS AINEO, I )=1.0 GO TO 110 IF (TT .LT. TBU )) GO TO 110 TTT = AMINHTT,TE ( I ))-TB(I ) GO TO (110,103,104) , IS A(NEO, I) = TTT GO TO 110 A ) / ( T ( LN+1 ) -T ( LN ) ) PX=AX(LN)+(AX(LN+1)-AX(LN) ) *TTT PY=AY(LN)+(AY(LN+1)-AY( LN) )*TTT B(NEO)=TX-PX C(NEO)=TY-PY CONTINUE REWIND LUF CAL=. FALSE. DO 900 1=1, NMX PRINT 74, ( A( I* J), J=1,NPAR) CALL LINLSQ(A,NRA,NEQ,NPAR,B,W,PARX, CALL LINLSO( A ,NRA , NEQ, NPAP., C, W, PARY, PRINT 74, (B( I ),C(I ) ,1 = 1, NMX) PRINT 74, (PAkX< I ) ,PARY<1 ),I=1,NPAR) PRINT 74, (X( I ),Y(I ), 1 = 1, NMX) PRINT 74, 1950 SMP I960 SMP 197 0 SMP 1980 SMP 1990 SMP 2000 SMP 2010 SMP 2020 SMP 2030 SMP 204 n SMP 2 05?) SMP 2060 SMP 2070 SMP 20 a 0 SMP 2090 SMP 2100 SMP 2110 SMP 2120 SMP 2130 SMP 2140 SMP 2150 SMP 2160 SMP 2170 SMP 2180 SMP 2190 SMP 2200 SMP 22 1"*C SMP 2220 SMP 2230 SMP 2240 SMP 2250 SMP 2260 SMP 2270 SMP 2280 SMP 2290 SMP 2300 SMP 2310 SMP 2320 SMP 2330 SMP 2340 SMP 2350 SMP 2360 SMP 2370 SMP 2380 SMP 2390 SMP 2400 865 CALCULATE 05 POSITIONS AND WRITE ALONG WITH FIXES. TFRST^TU) TLST=T(NLN) LN = 0 TP=TFRST+EPS CAL=. FALSE. IX=TFRST/DOR 1002 READ (LUF) TT, F A, FO, CSE, SPD , I FX , NEO, L CSE=CSE/RAD 1005 IF(TP-TT) 4j015, 1010, 1010 C WRITE F IX 1010 ETV=E01 VOS(CSE,SPU,FA) CALL PNAVC(TT,FA,FO,CSE,SPD, IFX,ETV,LCP) IF WEQ-NMX) 1002, 1014, 1014 J014 TT-9999. COMPUTE DR POSITION CHECK TO SEE THAT WE ARE ON HE CORRECT DR LINE 1015 IF > 1017,1017,1016 1016 LN=LN+1 TP=TP+EPS DT=T (LN+U-TI LN) PX=AX(LN+1 )-AX(LN) DY=AY(LN+1)-AY(LN) C VLO IS LOCAL VELOCITY SCALE IN CM/HR/KT VLO = FAC/COS(FLA( LN)*RAD ) VXB=VL0*SP4 LN)*SINICS( LN ) ) VYB=VLO-SP(LN ) "COS ( CS ( LN ) ) IF (ABS(TP-DDR/2.-T(LN) )-.45*DDR ) 1020,1020, 1017 C SET UP TO PUNCH POSITION OF LINE CORNER 1020 1X= IX-1 TP=T(LN) C INTERPOLATE ON UNCORRECTED DR LINE 1017 TTT=(TP-T(LN))/DT PX-AX(LN)+T1T*DX PY=AY-TB< I) GO TO ( 1101, 1103,1104) , IS 1103 PX=PX+TTT*PARX( I ) PY=PY+TTT*PARY( I) VX=VX+PARX( I ) VY=VY+PARY( I ) GO TO 1110 1104 VX=VX+TTT*PARX( I) VY=VY+TTT*PARY( I ) TTT=TTT**2*0.5 PX=PX+TTT-PARX(I ) PY=PY+TTT*PARY< I) 1110 CONTINUE 1215 CONTINUE SMP 2'. 10 SMP 2420 SMP "2 4'30 SMP 2440 SMP 24 50 SMP 2 4 60 SMP 2470 SMP 2480 SMP 2 490 SMP 2500 SMP 2510 SMP 2520 SMP 2530 SMP 2540 SMP 2550 SMP 2560 SMP 2 570 SMP 2580 SMP 2590 SMP 260O SMP 2610 SMP 2620 SMP 2630 SMP 2640 SMP 2650 SMP 2660 SMP 2670 SMP 2680 SMP 2690 SMP 2700 SMP 2710 SMP 2720 SMP 2730 SMP 2740 SMP 2750 SMP 2760 SMP 2770 SMP 2780 SMP 2790 SMP 2800 SMP 2810 SMP 2820 SMP 2830 SMP 28-40 SMP 2850 SMP 2860 SMP 2870 SMP 2880 SMP 2890 SMP 2900 SMP 2910 SMP 2920 SMP 2930 SMP 2940 SMP 2950 SMP 2960 SMP 2970 SMP 2980 SMP 2990 SMP 3000 866 1216 1217 12)9 1218 TSPD=VX< VX+VY' VY lF(TSF'U) 1216,1216,1217 TSPD=0. 0 TCSE--0.0 GO TO 12 18 TSPO=SORT { TSPD) /VLO TC SE=ATAN2 ( VX, VY J/RAD IF (TCSL) 1 219, 1218, 1218 TC SE-TCSF. + 360. CONTINUE CONVERT FROM M AF^'COORD 1 NATE S TO LAT,LON AND WRITE DR POS CALL MERC ( F L T , F LO , P X , PY , 3 ) ETV=EOTVOS(TCSE,TSPD,FLT) CALL PNAVC ( TPtFl T, FLO , TCS£ , TSPD, IDR,ETV,LCP) IF (CAD GU TO 2000 IX=IX+1 TP=PLOAT ( IX)*DOR IF(TP-TLST) 1005,1220,1220 1220 CAL=.T' SKP 36?,0 SMP 3 6'.0 SMP 3650 SKP 366 0 Sf'.P 3<>7 0 SMP 36fi0 SMP 3690 SMP 3700 868 SUBROUTINE MERC ( A , B, C, 0, 1 CON ) C FLATTENING FOR INTERNATIONAL SP HE KU I D= 1 /297 DATA PlFOR/0.7 85 390 16/,RAD/0.Ol7<,532V2 5/',EPS/.08199109O5/ CALLING SEQUENCE COMPUTE MERCATOR COORDINATES FROM LAT.LON. (. C c c c c c c c c CA CALL HEKCI A, Q,C ,0,ICON ) DEFINE TRANSFORMATION 1CCN=1 A,B = LAT, LCIN IN DE.GRESS OF ORIGIN C- SCALE IN INCHES/DEGREE D=UUMMY '' CONVERT COORDINATES IC0N=2 AfB=LAT,LON OF POINT C,0=X,Y IN CM. FROM M; TRANSFORM MAP COORDINATES OF MERCATOR COORDINATE SYSTEM. '.P ORIGIN TO LAT.LON 1C0N=3 FOR IC0,N = 2 LL1NG PARAMETERS SAME AS GO TO ( 1 ,10,50), ICON 1 SCALE=C*2, 540005 RSCAL = SCAL .E/RAD SCALE IS IN CM/DcGREE 10 X=SCALE*B RPHI-A-RAD EPS1N=SIN(RPHI )-EPS Y = RSCAL-ALOG! TAiJ( PirOR+RPHl*. 5) *(( l.-EPS IN)/ ( l.+EPSIN) )** (EPS- GO TO <20,iO) , ICON 20 XBASE=X YE'.ASE = Y 25 RETURN 30 C'X-XBASE D=Y-YBASE 35 RETURN 50 B= (C+XBASE J/SCALE FAC=EXP( (D+YEASE)/R$CAL ) EPSIN = EPS*SI.\(2.*(ATAMFAC)-PIF0R) ) E-2.*(ATAN(FAC*< ( 1 . +EPS IN ) /( 1. -EPS IN ) ) **( EPS*. 5 ) ) -PI FOR ) EPSIN=EPS*SIN(E> A=2.*(ATAN(FAC*( ( 1 . +EPS IN ) /( 1 . -E PS I N ) ) ** ( E PS *. 5 ) ) -P I FOR ) /R AD RETURN END .5) MEk HER MEK MLR M EP. MLR MER MEK HER ML'r'. MER MER MLR MER MER M E R HEP, M fc R MER MER ME P. MEk M E.R ) M £ R MFR MER MFR MER MFR MER MER MER MER MER MER MER MER MER MER 10 20 30 40 50 60 70 bo 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 2*'0 250 260 270 280 290 300 310 320 330 340 350 360 37C 380 390 869 SUBROUTINE TYPE (T»oDAY,FH) CONVERTS TIM? T PEASUKEO ! f-i HOURS FROM THE BEGINNING OF C JULIAN DATE JDAY AND FH WHICH IS HR.MIN DATA ROUND /O . ' >9999999999/ ITF(1P=T«60. + |,.C)UNO JDAY= I TEMP/ l'VAO ITEM P = ITEMP-1440*JDAY IH=ITEMP/60 ITEMP=ITEMP-IH*AO FH=FLOATi IH)+FLl)AT( I TEMP 1/1 00. RETURN END THE YEAR TO TYM 10 TYM 20 TY(1 :^n TYM 10 TYM '>o TYM 60 TYM 70 TYM 6 0 TYM °0 TYM 100 TYM 110 TYM 120 870 SUBROUTINE L 1MSOI A ,NRA ,NOB, NPAR , C , W, B ,E , F , AI ,DET ) LIN 10 C SOLVES THE MATRIX EQUATION A=J-8=C WHEPE THE SYSTEM IS EVENDETEPvM I NED ORLIN 2q C OVEROETERKINED WITH THE UBSERVAT IONAL EQUATIONS WEIGHTED BY THE LIN 3d C VECTOR W. LIN a.j C NRA IS THE DECLARED ROW DIMENSION Of~- A LJN 1 0 C NOB IS THE NUMBER OF EQUATIONS (THE NUMBER OF ROUS OF A ACTUALLY USEDJLJN fO C NPAR IS THE DIMENSION OF B AND C (THE NUMBER OF UNKNOWNS) LIN 7t C E HILL CONTAIN THE RESIDUAL VECTOR LIN 80 C F WILL CONTAIN THE ESTIMATED STANDARD DEVIATION OF THE PARAMETERS L 1 N 9i. C AI WILL CON1AIN THE INVERSE OF THE OF THE NORMAL MATRIX LIN loo C DET WILL CONTAIN THE DETEERM NANT OF THE NORMAL MATRIX LIN 1)0 DIMENSION A (MR A,. NPAR ) , A I ( NPAR , NPAR ), B ( NOB ), C (NOB) , W (NOB ) , E ( NOB ) , L I N 3 20 * F (NPAR ) LIN \Z0 C WIEGHT LIN J'iO DATA LOUT/6/ l. I H ) 50 DO 11 1=1, NOB LIN )6C DO 10 J-l ,NPAR LIN 170 10 A (ft J)=A( I, J)*WU) LJN 1B0 11 C ( I )^C ( I )*W< I ) LIN K-C C IF SYSTEM IS EVENUETERMINEDtSKIP TRANSPOSE- MULTIPLICATION. LIN 200 IF (NOB . FQ. NPAR) GO TO 670 LIN 210 C PREMULTJPLY BY A TRANSPOSE LIN 22C 00 550 J=1,NPAR LI N 230 DO 550 1=1, NPAR LIN ?«Q SUM=0.0 LIN 250 00 525 K=1,N0B LIN 260 525 SUM=SUM + A(K, J)#A(K, 1*> LIN 270 550 AI ( J, I )=SUM LIN 280 GO TO 680 LIN 290 670 DO 675 1=1, NPAR LIN 200 00 675 J = 1,N0B" LIN 310 675 AI(J,I)=A(J,I) LIN 320 680 CONTINUE LIN 330 C SOLVE SYSTEM LIN 340 CALL M1NV(AI, NPAR, DET, E ,F) LIN 350 C F=C*AT LIN 360 IF (NOB. NE .NPAR) GO TO 562 LIN 370 00 563 J=1,NPAR LIN 3E0 563 F(J)=C(J) LIN 390 GO TO 561 LIN AOO 562 DO 650 J=1,NPAR LIN 41C SUM=0.0 LIN 420 DO 625 K=1,N0B LIN 430 625 SUM=SUM+A(K, J)*C(K) LIN 440 650 F(J)=SUM LIN 450 C B=Al*F LIN 460 561 CALL GMPRD( AI,F,B, NPAR, NPAR, 1) LIN 470 SUM=0.0 LIN 4fcO DO 700 1=1, NOB LIN 490 TEMP=.0 LIN 50O COMPUTE RESIDUALS LIN 510 DO 690 J=1,NPAR LIN 520 690 TEMP=TEMP+B( J)*A{ I, J) LIN 530 TEMP=C( D-TEKP LIN 540 SUM=SUM+TEMP*TEMP LIN 550 E(1)=TEMP/W(I ) LIN 560 C UNSCALE OBSERVATIONS LIN 57C CI()-C(1)/H(I) LIN 580 D0'700 J=1,NPAR LIN 590 A(I,J)=A( I, J)/W ( I ) LIN 600 871 700 CONTINUE ip (nob .eo. npar) return sigmsqasum/fl0at(n06-npar-) 00 705 i = i,;jpar FAC=AI (1,1 )*SIGMSCi TEMP^SQRTI »U>S(FAC) ) 705 F( 1 )=SIGN(TEMP,FAC) RETURN It* FORMAT(5E12.3) END LIN LI N LIN LIN LIN LI N LIN LIN LIN LIN 610 620 630 640 650 660 670 680 690 700 872 SUBROUTINE PNAVC ( T 1ME, FLAT, FLON , CSE , SPD, IT » ETV ,LOUT ) C PUNCHES A CARD I M M ^+ G NAVIGATION FORMAT C TIME IS IN HOURS FROM THE BEGINNING OF THE YE AR , FL A T , F LUN , C SE IN DEG, C SPD IN KNOTS. C LM DORM AN AOML JUN 1973 DATA 1B,NM,R0UND/1H , 1H- , 0. 49999999999/ 1F(F1AT)2,1,1 1 ISA=IB GO TO 3 2 1SA-NM 3 CONT INUE IF(FLON) 5,4,4 4 IS0=1B GO TO 6 5 ISO=MM 6 CONTINUE IT EM P= IF IX ( T1ME*600.+R0UND) 1DA=I TEMP/14400 1 T EM P= I TEMP- 14400* I DA IH=ITEMP/600 IM=1TEMP-600*IH 1TEMP=IFIX(6000.*ABS( F LAT )+ ROUND ) 1LA- ITEMP/fcOOO IAM=JTEMP-I LA*6000 ITEM P= IF IX(6000.*ABS(FL0N)+R0UND) ILO=ITEMP/6OG0 IOM=ITEMP-II.O*6000 1CS=IF IX( 10.*CSE+ ROUND) ISP=1F IX ( 10.-SPD+R0UMD) 1EC=IF IX(ETV*100.+R0UND) WRITE (LOUT, 7 1 ) IU A , 1 H , I M, 1 SA, I L A, I AM, I SO , I LO , I OM , I C S , J Sr , I T , I E C 71 FORMAT (1X,313,2X,A1,I2, 1X,I4,1X,A1,I3,3(1X,I4),1X,A2,,1X,I6) RETURN END PNA 10 PNA 20 PN'A 2C PNA 40 PNA bO PNA 6o PNA 7 0 PNA f C PN A 90 P N A ICO PNA no PNA IPO PNA no PNA 140 PNA ISO PNA 160 PNA 170 PNA 130 PNA 190 PNA 200 PNA 210 PNA 220 PNA 2 30 PNA 2',C PNA 2^0 PNA 26G PNA 27 0 PNA 2L-: PNA 2S0 PNA 300 PNA 310 PNA 320 PNA 330 PNA 340 873 DIMENSION ALAT( 10) , ALONG! 10) RfcAD(5, 102) N IN, MOOT , NSC RAT ,NPLOT, I DELT , NLAT ,NLONG, A 102 FORMAT! 7 15.F10.5 ) RE AO (5, 101) '(ALAT(l) t 1*1 t NLAT) RE AD (5, 10 1 ) ( ALOMGt I ),I =1 , NLONG) 101 FORMAT! 8F1 0.3) REW I NO N IN REWIND NSCRAT CALL OR AW L ( AL AT, ALONG, N LONG, NLAT, A, I DE LT , N IN ,NOOT , NSCRAT ,NPLOT ) END DRA 10 PR A 20 DRA 30 DRA '♦0 DRA bO DRA 60 DRA 7 0 DRA b a DRA 90 DRA ICO 874 SUBROUTINE DRAWL! ALAT, ALONG f NX, NY, A, IDELT,N IN ,NOUT,NSCAT ,NPLOT) DRW In C DRW ?0 C Al'\T= ONE DIMENSIONAL ARRAY WITH NY .GE . 2 . AND .LE . 1 0 IN DECIMAL DEGREES DRW 30 C ASCENDING SEOJENCE ( WhOL E OR HALF DEGREES ONLY) DRW <\(j C ALONG= ONE DIMENSIONAL ARRAY WITH NX. GE . 2 . AND.LE . 10 IN DECIMAL DEGREESDRW 50 C ACCEKDING SEQUENCE (WEST OF GREENWICH NECA T I V E ) ( KHOL & OR HALF DEREES ODRW 60 C A= SCALE If; INCHES/DEGREE DRW 7r; C IDELT= TIME INCREMENT IN MINUTES AT WHICH TIME TICKS WILL BE MADE DRW BO C (CHECKS WIN FOR INTEGRAL MULTIPLES OF THIS UNIT) DRW 90 C N1N = INPUT TAPfc NUMBER IN BCD MGG FORMAT (ONE FILE) DRW 100 C NOUT=PRINTED OUTPUT TAPE NUMBER DRW 110 C NPLOT- PLOTTING TAPE NUMBER DRW 120 C NSCAT= SCRATCH TAPE NUMBER DRW 130 C DRW 140 DIMENSION ALAT( 10 ) ,ALONG( 10 ),XF ( 10) , YF ( 10) , IBUF( 1500) ,RFX< 10) DRW ISO 1 ,RFY(10) , LMA( 10) , LNA(IO) DRW 160 DIMENSION U(4),IS(4) DRW 170 INTEGER W0RD,W0RD1,W0P.D2 , DRW 180 DATA PI,P'.;, EPS/3. 1415926, 28. 0.1.0E-5/ DRW 190 DATA W0RD1 , WQRD2/2H.DR , 2 HUP/ DRW 200 DATA I A( 1 ) , I A( 2 ) , IA( 3) , I A(4 ) , NW0RD/2HSA t 2H0M , 2HLC , 2HL A , 4 / DRW 2)0 DATA 1S( 1 ) , I S< 2) , I S ( 3), IS(4) , 1SDFLT/2, 12,0,5, 11/ DRW 220 RAD«X)=PI /130.0-X DRW 230 C DRW 24'0 C DRW 2 50 WRITE (NOUT, 106 ) N I N , NOU T, NSC AT , NPL OT , A , I DE LT , ( AL AT ( I ) , I = 1 , NY ) DRW 260 106 FnRMAT(74HlSUBR0UTINE DRAWL HAS BEEN CALLED WITH THE FOLLOWING ARGDRW 270 1UMENT ASSIGNMENTS, , /5X, 15H1NPUT TAPE , 1 6 , / 5X , 15H0UT PUT TAPE OR!-.' 280 2 , I6,/5X, 15HSCRATCH TAPE , I 6, /5X, 14HPL0T TAPE , I 7 , //5X , 17HTH0RW 2r,0 3E PLOT SCALE IS,F10.4,28H INCHES/DEGREE OF LONGITUDE , /5X , 16H.T IME DRW 300 4T1CK^ EVERY, 111, 10H MI NUT E S , / /5X , 24ITL AT I T UDE BOUNDS ARE ,10FDR'.: 310 510.3) DRW 320 WRITE (NOUT, 107) ( ALONG ( I ) , I = 1 , NX) DRW 330 107 F0RMAT(5X,24HL0NGITUDE BOUNDS ARE .10F10.3) DRW 340 DELT=FL0A1 ( IDELT)/2'< .0/60.0 DRW 350 IF (DELT.LT. ( 1.0/24.0/60.0 )) DEL T= ( 1 0 . 0/24 .0/60 . 0 ) DRW 36n DO 1 1=1, NX DRW 370 RFX( I )=RAD( ALONG! I ) ) DRW 380 IF (RFX( I ).LT.0.0) RFXd ) = 2 .0*P I + RF X ( I ) DRW 390 1 CALL MERK(0.0,RRR,RFX(I ),XF( I) ,A, + 1 ) DRW 400 DO 2 J=1,NY DRW 410 RFY( J)=RAD( ALAT( J) ) DRW 42D 2 CALL MERK(RFY( J) , YF ( J) ,0.0, RRR, A,+l) DRW 430 IRX = NX-1 DRW 4^.0 IRY=NY-1 DRW 450 DO 80 1=2, NY DRW 460 DIFF=YF ( I )-YF ( 1-1 ) DRW 470 IF (DIFF.LE.PW) GO TO 80 DRW 480 WRITE (NOUT, 103) DRW 490 103 FORMAT) 105H1Y0UR CHOSEN LATITUDE MAP BOUNDS WOULD RECU1RE A PLOTTIDRW 500 • 1G SHEET LARGER THAN THIRTY INCHES. PROGRAM STOPS.) DRW 510 STOP DRW 520 80 CONTINUE DRW 530 C DRW 540 18 I2XA=0 DRW 550 1ZYA=0 DRW 560 15 READININ, 161 ) I TEM, DAY ,T 1 , T 2, YL AT, YLATM , XLONG , XLONGM , ALPHA, V ,WORD DRW 570 IF JDAY.GT. 990.0 ) GO TO 16 DRW 5B0 161 FORMAT! I1,2F3.0,F3.1,2X, F3.0, IX , F4. 2 , IX , F4.0 , IX , F4. 2 , 1X,F4.1,2X DRW 590 1 F3.1,1X,A2) DRW 600 875 T]ME = DAY*Tl/2'V.0+T2/'?4.0/lbu .0 YLAT=RAD ( YLAH S1GM( YLA1 f;, VLAT) /60.0) XLONR-RADI XLLiNGfSIGf-; ( XLONGM ,XL0N0,) /60, IF ( XLONG. IT, 0.0) XLG.\G-2.0*PI+XL0NG CALL MtRK(YLAT,Y,XLDNG,X,A,+l) DO 11 J=i, IKX DO 11 K=1,IRY JJ = J KK=K IF ( ( (X. LE.XFU+1) ) ,AND.(X.GT.XF< J) ) J , 1 (Y.GT.YF (K) ) ) ) GO TO 12 0) AND. ( (Y.LE.YF (K+l ) ) .AND. 11 12 HI 6 71 77 16 133 181 38 34 36 10 18 (IZY.EQ. IZYA) ) GO TO 6 CONT INUE GO TO 18 IZX=JJ 1 ZY = KK IF ( WORD. EO. WORD 2 ) GO IF (( IZX.EO. IZX A J.AND. WRITE (NSCAT*) X , Y, YLA T, XLONG f I ZX , I ZY , T ICE ,V, ALPHA, IC WRITE INOUT, 111 ) X,Y,YLAT, XLONG, IZX, IZY ,TIKE,V, ALPHA, IC FORMAT ( IX, 4C 12. 5, 2 16 ,3 El 2. 5, 16) IF ( WORD. Nfc. WORD 1) GO TO 7 IC = 1 IT IMF. -IF IX(TIME/DELT+.49) TEST = T IME-F4.0AT ( I T ICE ) *OELT IF (A8S(TLST).LT..0007 ) 1 C= 3 CO TO 77 IC=IS0FLT+?0 DO 7) M=1,N'/.'0RD IF (W0RD.EQ.1AIM)) !C=IS(M) + 20 CONT INUE WRITE (NSCA'T) X,Y,YL AT, XLONG, IZX, IZY ,TIME, V , ALPHA, IC WRITE (NOUT, 111) X,Y, YL AT, XLONG, IZX, IZY, T IME ,V,. ALPHA, I C IZXA=IZX IZYA=IZY GO TO 15 IC=9 WRITE (NSCAT) X , Y , YL AT , XLONG, IZX, IZY, TIME, V, ALPHA, IC REWIND NSCAT WRITE(N0UT,133) F0RMAT(//15H FILE COMPLETE.) X,Y,YL AT, XLONG, IZX, IZY , T IME , V , ALPHA, I C GO TO 38 POINTS OUTSIDE PLOT AREA.) READ (NSCAT) IF (IC.NE.9) WRITE(N0UT,181) FORMAT (30H0ALL RETURN JZ = 1 LMA( 1)=1 LNA(1)=1 IF ( HRX.EO.D.AND. (IRY.EO.D) LMAI1)=IZX LNA(1)=IZY READ (NSCAT) X , Y , YLAT , XLONG, IZX, I ZY, T IME , V , ALPHA , IC IF ( 1C.EQ.9) GO TO 35 DO 36 JI=1,JZ IF (( IZX.EO. LMAIJI )). AND. HZY.EQ . LNA< J I )) ) GO TO 34 CONTINUE JZ=JZ+l GO TO 35 DRW 610 DRV 620 DRW 6 30 DRW 640 DRW 650 DRW 660 DRW 67C DRV.' 6 S 0 DRW 69 0 DRW 7 00 DRW 710 DRW 7 2 0 DRW 7 30 DRW 740 DRW 7 SO DRW 760 DRW 77 0 DRW 730 DRW 7 90 DRW 800 DRW 810 DRW 82G DRW S30 DRW 840 DRK 8 50 DRW 660 DRW 8 70 DRW 880 DRW 890 DRW 900 DRW 910 DRW 9 20 DRW 930 DRW 940 DRW 9 50 DRW 960 DRW 970 DRW 980 DRW 990 DRW 1000 DRW 1010 DRW 1020 DRW 1030 DRW 1040 DRW 1050 DRW 1060 DRW 1070 DRW 1080 DRW 1090 DRW 1100 DRW 1110 DRW 1120 DRW 1130 DRW 1140 DRW 1150 DRW 1 160 DRW 1170 DRW 1180 DRW 1190 DRW 1200 876 35 150 110 53 52 54 55 59 57 188 LMA( JZ ) = IZX LNA( JZ ) = IZY GO TO 34 CONT INUE PLOTT IMG PACKAGE OF A PLOT TAPE HAS BEGON.) TORN AT ( 3 5HOCRF AT ION WRITE (i\-OUT, 150) CALL PLOTS! IS UP , 1 5 00 • HP LOT ) CALL PLOT (O'.O, -30. 0,-3) CALL SYMBOL! 1.0,9.9, .28 , 2 PHMACH INE ASSISTEO SMOOTH PLOT , 90 . 0 t 28 ) CALL SY.\3()L( 1.42, 12. 1, .2 1, 1 6HN0AA/AGML/M I AM I ,9 0.0, 16) XREF=0.0 YREFLD=0.0 WRITEC.OUT, 110) JZ FORMAT (33H0NUMBER OF MAPS BEING PRODUCED IS t 16 ) 00 51 1=1, J Z rev; if: d nscat LM=LMA( I ) LN=LNA< I ) yref=(pw+1.37-(yf t ln+1) -yf (ln) ) ) /2.0-yrefld yrefld=(pw+1. 37- ( yf( ln + 1 )-yf( ln) ) ) /2.0 xrff=x?;ef-i5.o CALL PLOT ( X'RL-F, YREF,-3) CALL SYMBOL < -2. 5 ,0.0,. 14, 4, 0.0,- 1 ) CALL PLOTlb.0,0.0,3) JN=IF1X( ( RFYILN+1 1-RFYI LN ) )/( . 5*PI/ 180.0 ) + 1 . OE-4 ) + 1 IN=iFJX< (RFX{LM+1)-RFX(LM ))/(.5=PI/180.0)+1.0E-4)+l XREF=FLOAT ( IN-1)*A*.5+. 25 YREF=YF ITRIP=+1 READ (NSCAT) X , Y , YLAT,XLONG , 1 ZX , IZY, TIME ,V,ALPHA,IC IF (IC.E0.9) GO TO 51 IF ( ( IZX.NE.LMl.GR. ( IZY.NE.LN) ) GO TO 57 X=X-XF ( IZX) Y=Y-YF( IZY ) WRITE (NOUT, 188) X,Y,IC FORMAT! 1X,2E14.5, 110) ALPHA=AMOO( I 4 50.0- ALP HA) ,360.0) TIME=(TIME+EPS) DRW 1 210 DRW 12 20 DRW i;>' DP.W 12'-0 DRW 1 2 V DRW 12;' DRW 1270 DRW 1 2m) DRW 12o,-i DRW 13 1 ;i DRW 1310 Dr.;; i '?.:•: ■.■ DRW 1 33: DRW 1 34 0 DRW l?.5'-i DRW 13> . DRW 1370 DRW 1 3 ;•.■:■■ DRW 13V.' DRW 1 ', J V DRW 1 * i •: DRW 1420 DRW 14 30 DRW 1440 DRW1 14 &f! DRW 14 60 DRW 147': DRW 14,';(! DRW 14'.'.) DP>' 15 00 DRW 1510 DRW 1 5 ?. " DRW 1530 DRW 1-540 DRW 1550 DRW 15 6': DRW 157;; DRW 1 5 P 0 DRW 1590 DRW 16 00 DRW 1610 DRW 1620 DRW 16 30 DRW 164 0 DRW 1650 DRW 1660 DRW 1670 DRW 168 0 DRW 1690 DRW 1700 DRW 1710 DRW 1720 DRW 1730 DRW 1740 DRW 1750 DRW 1760 DRW 1770 DRW 17flO DRW 1790 DRW 1800 877 IT IMF = IF I X ( TIME ) 10UIT=IC IF ( I0UIT.GE.2O ) IQUIT=2 GO TO 161,62,63,6*) , ICJU IT 61 corn iuve IF ( ITRIP. 60.-1) CALL P LOT (RXPAGE , RYPAGE, 3 ) CALL PL0T(X,Y,2> GO TO 59 62 IC = IC-20 IANN=0 IF (ITRIP. EO.l) CALL WHERE ( RXPAGE , RYPAGE , .5 ) CALL SYMBOL(X,Yt .07, I C , 0.0,-1) XHR = ( ( TIME -FLOAT! IT I ME ) ) *=2«.0 + EPS) IHR= IF IX (XHR ) XMJN)= ( ( TIME-FLOAT ( I T I M E ) -FL OAT ( I HR ) /2* . 0 ) < 6 0 .0*24 . 0 + E PS ) XHR --FLO AT ( IHR i =: 1 CO . C + X.'. IN 66 IF (ALPHA. GT.!?0.0. AND. ALPHA. LT. 270.0) AL PHA = ALPHA + 180 .0 ALPHA=AMOD( ALPHA, 360.0) IF ( ALPHA. GE. 270.0) ALPH A=A LPHA-360. 0 ALFHA = ALPHA+S1G;J ( 90 .0 , ( -ALPHA ) ) ALPHf> = RAD( ALPHA) CALL NUMBER ( IX+. 11*C0SI ALPHB) ) , { Y+. I 1*SIN ( ALPHB ) ) , .07 »XHR , ALPHA 1,-1) IF ( IANN.EQ.1) GO TO 6 7 IF (ITRIP. EO.l) CALL PLOT ( R XPAGE , RYPAGE , 3 ) ITRIP=-1 GO TO 57 63 CONT INUE IF ( ITRIP. EO.-l ) CALL PLOT ( RXPAGE , RYPAGE , 3 ) CALL SYM60L(X,Y, .07, 13, ALPHA, -2) XHR sTIME-PLOATUTIME) IF (ABS( XHR) .GT.2.0E-5) GO TO 59 XHR = T I ME CALL SYMBOL (X,Y, .07 , 11 , ALPHA, -2) IANN=1 GO TO 66 67 CALL SYMB0L1999. 0,999.0, .07, 5H/0000, ALPHA, 5) CALL PL0T(X,Y,3) GO TO 59 64 CALL PL0T(X,Y,3) GO TO 59 51 CALL SYMB0L(-2.5,0.0,.14,3,0.0,-1) XREF=XREF+5.0 CALL SYMBOLJXREF, (YREF/2.0-1.40) ,.28,10HEND OF JOB, 90. 0,10) CALL PLOT (0.0,(YREF/2.0- 1.40) »-3) CALL PLOT(XREF ,0.0,999) WR1TE(N0UT, 162) 162 FORMAT! 15H0PL0T FINISHED.) RETURN ENO DRW lain DRW 16 20 DRW 1830 DRW ISfO DRW ie?o DRW I860 DRW 1S7C DRW ) »ao DRW isO;: DRK 190C. DRW i r i : o Okw 1920 DRW 1^30 DRw 19^0 DRW 19 00 DRW I960 DRW 19 70 DRW 19 BO DRW 199C DRW 2000 DRV! ? 0 i 0 DRW ?010 DRW 20 30 DRW 204 0 DRW ?r,<)Q DRW 2060 DRW 2070 DRW 2 060 DRW 209C DRW 2100 DRW 2 i 1 0 DRW 2120 DRW 21 30 DRW 21'tO DRW 2150 DRW 2160 DRW 2170 DRW 2180 DRW 2190 DRW 2200 DRW 2210 DRW 2220 DRW 2230 DRW 22*0 DRW 2250 DRW 2260 DRW 2270 DRW 2280 DRW 2290 DRW 2300 878 SUBROUTINE: PASTA ( IT YPE,XX,X , Y , S I Z E , ANOL L ) THIS ROU 1TYPE-CO XX=L AT IT X=HORI ZO Y = VERT 1C SIZE=PLO ANGLE --AN DIME DATA DATA DATA Z-XX ( IF IF ( IF ( IF ( IF ( Z = AB Z = Z* NVAL NM IN XNVA XNM I CALL CALL CALL CALL CALL RETU END TINE IS NTKOL C UDE OK NTAL PCI AL POSI T HE IGM CLE OF NSION X- XNOTE ( BLANC/ PI/ 3.1 XX.GT.P ITYPE.t ( I TYPE . ITYPc.E ( ITYPE. S(Z) 180.0/3 =-IFIX(Z =IFIX( < L=FLOAT N=FLOAT NUMBER SYMBOL NUMBER SYMBOL SYMBOL RN USED IN THE ANNOTATION OF A MERCATOR CHART. ODE (ONE FOR LAT1TUUE AND TWO FUR LONGITUDE) LONGITUDE IN RADIANS S IT ION OF ANNOTAT ION TIDN OF ANNOTATION T OF AwNOTAT ION ANNOTATION W0TE<4) 1 ) , XNOTE (2) 1H / 41 5926/ XNOTE ( 3), XNOTE (4) /INN, 1 HE t 1HS, 1HW/ I) Z=XX-2.0*PI 0. 1) WORO = Xi\OTE( 1) I 0. 1 ) .AND. (Z .LT.0.0 ) ) 0.2) W0F;D = XN0TE( 2) LQ.2) .AMD. (Z .LT.0.0) ) . 1415926+1. OE-4 WORD=XNOTE (3) WORD=XNOTE (4) Z-FLOATJNVAL ) ) *60 .0+1 . 0E-4 ) (NVAL) ( N h I N J (X,Y,SIZE, XNVAL, ANGLE, -1 ) (999.0,999.0 , S I ZE , BLANC , ANGLE , 1 ) (999.0,999.0, SIZE, XNM IN, ANGLE , -1 ) ( 999. 0,9 99.0, SIZE, BLANC, ANGLE, 1 ) (999.0,999.0, S I Z E , WORD , ANGLE , 1 ) PAS 1 ') PAS 20 PAS 30 PAS 4G PAS 5 0 PAS 60 PAS 70 PAS 60 PAS 9 0 PAS 10Q PAS 1 10 PAS 1 20 PAS 130 PAS 14Q PAS 15C PAS 160 PAS 170 PAS 180 PAS 190 PAS 200 PAS 2)0 PAS 220 PAS 2 30 PAS 240 PAS 250 PAS 260 PAS 270 PAS 280 PAS 290 PAS 300 PAS 310 PAS 320 PAS 330 879 SUBROUTINE MERMPHI , Y , L AMD A, X , A, ITRIP) ANGULAR VALUES IN RADIANS, A IN ITRIP. EO.l IF FORWARD TRANSFORM INTERNATIONAL SPHEROID LAVELLE/AUML/JUNE 197 2 INCHES/DEGREE, AND ITRIP. EQ.- 1 IS REAL LAMDA OAT A WEE tP I /8» 1991 8905E -2 t 3. 1*15926535/ IF ( ITRIP. EO.-) ) GO TO 1 X=A*180.0/PI -LAMDA Y = A*H!0.0/PI*ALOG(TAN(PI /4. O+PH 1 / 2 . 0 ) *( ( 1 ,0-WEE*SlN 1 WEE'\SIN -PI/4.0) PH1=2.0*( Al AN(EXP(Y/A/180.0*PI ) /( ( 1 . O-WE E*S I N ( PH I ) ) /( 1 1 *SIN(PHI ) ) )**(WEE/2.0) !-Pl/4.0) LAKUA=X/A/180.0*PI RETURN ENO MRK 10 MRK 20 MRK 30 INVERSE. MRK 40 MRK t>0 MRK 6 0 MRK 70 MRK 80 MRK 90 MRK 100 MRK 1 10 I ) ) /( 1.0 + MRK 120 MRK 130 MRK 140 MRK ISO O + WEE MRK 160 MRK 170 .O+WEE MRK 180 MRK 190 MRK 200 MRK 210 MRK 220 880 Data 881 10 34 7 5 6 ? 4 1 00 0050 094 5 TP 100 0100 16 336 -59 091 0 94 5 5A 100 0130 097 5 TP 100 0144 16 339 -59 052 097 5 SA 100 0246 16 338 -58 598 097 5 SA 100 0330 16 337 -58 560 097 5 SA 100 0 6 06 16 333 -58 423 097 5 SA 100 0706 16 330 -58 371 097 5 SA 100 0752 16 327 -58 332 097 b SA 100 0830 002 5 TP 100 0902 16 350 -58 297 00 2 5 SA 100 1052 16 456 -58 299 002 5 SA 100 1244 16 562 -58 296 00 2 5 SA 100 1320 270 63 TP 100 1334 16 597 -58 309 270 6 3 SA 100 1415 004 55 TP 100 1432 17 009 -58 351 004 b b SA 100 1514 17 049 -58 353 004 5b SA 100 1615 269 63 TP 100 1646 ) 7 113 -58 380 269 63 SA 100 1715 090 05 TP 100 1752 17 111 -58 397 090 5 SA 100 1830 17 113 -58 362 090 5 SA 100 1915 270 0 5 TP 100 1936 17 109 -58 337 270 5 SA 100 2018 17 109 -5 8 385 2 70 5 SA 100 2100 268 05 TP 100 2214 17 119 -58 509 268 5 SA 100 2230 266 05 TP 101 0156 17 125 -59 134 266 5 SA 101 0240 266 5 NA 101 0240 17 124 -5 9 178 266 5 SA 101 0336 17 122 -59 238 266 5 SA 101 0428 17 118 -59 292 266 5 SA 101 0616 17 096 -59 397 266 5 SA 101 0700 266 5 NA 101 0700 17 085 -59 451 266 5 SA 101 0730 273 05 TP 101 oeo4 17 075 -59 515 273 5 SA 101 0848 17 067 -59 560 273 5 SA 101 0915 277 05 TP 101 1000 17 071 -60 039 277 5 SA 101 1251 282 05 TP 101 1300 292 05 TP 101 1320 270 05 TP 101 1332 17 108 -60 257 2 70 5 SA 101 1428 17 115 -60 311 270 5 SA 101 1518 17 124 -60 351 270 5 SA 101 1550 99999999 101 1550 038 16 TP 101 1614 17 174 -60 351 0 38 16 SA 101 1740 17 357 -60 215 038 16 SA 101 1846 17 48 9 -60 113 0 38 16 SA 101 1910 99999999 101 1910 090 06 TP 101 1928 17 534 -60 054 090 6 SA 101 1940 180 05 TP 882 GEOPHYSICS, VOL. 39, NO. 1 (FEBRUARY 1974), P. 33-38, 2 FIGS. THE USE OF NONLINEAR FUNCTIONAL EXPANSIONS IN CALCULATION OF THE TERRAIN EFFECT IN AIRBORNE AND MARINE GRAVIMETRY AND GRADIOMETRYf LEROY M. DORMAN* and BRIAN T. R. LEWIS} The terrain corrections for gravity and gravity gradient data are nonlinear functional of the sur- rounding topography. We show how to approxi- mate these corrections by use of Volterra- Wiener functional expansion, which is a sum of linear con- volutions using the topography, the square of the topography, etc. The convolution kernels are like Taylor expansion coefficients which depend upon the distance from the source point to the field point. As an example, we compute the field Va for a two-dimensional ridge by the expansion method and compare the result with the exact result. We then show how the expansion technique can be used to propagate statistical properties through nonlinear functionals. As an example of this, we compute the rms terrain correction for Vzt as a function of the flight elevation and terrain re- lief. INTRODUCTION When measurements of the earth's gravita- tional field and its various derivatives are made with the goal of exploring subterranean struc- tures, it is necessary to make corrections for cer- tain gravitational fields. These are (1) the sym- metric main field of the earth, (2) the field from the terrain, and (3) the field from its isostatic compensation and other regional effects. To re- move the first we subtract the measured field from some standard such as the International Gravity Formula of 1924, including the associated elevation term. For the second, the Bouguer plate correction supplemented by a terrain correction is generally used. The dominant wavelengths of the field from the isostatic compensation are longer than 100 km (Dorman and Lewis, 1970; Lewis and Dorman, 1970), and are generally re- moved by subtracting a very smoothed form of the data after the first two corrections have been made. We discuss in this paper a treatment of the ter- rain effect applicable to the gravity and gravity gradient fields observed from the air and at sea. The computation of the terrain corrections is tedious and time consuming. The application of digital computers to this problem (Bott, 1959; Kane, 1962) is hindered by the extreme sensitivity of the measuring device to very near objects due to the fact that these fields fall off as some power of the inverse of the distance to the disturbance. DEVELOPMENT OF THE TERRAIN IN EXPANSION FORM We use a rectangular coordinate system locat- ing a point in space with the two-dimensional location vector x and the elevation z. At the point of observation x0, z0, the gravita- tional potential due to topography of elevation h{x) and uniform density p is v(x0, Zo) /oo /• as /% h(x -oo J -ai J 0 h(x) dzd2x (1) [|x-Xo|2+(3-Zo)2]1/2 where g is the gravitational constant. The vertical component of gravity Vx at the point of observa- tion is the derivative of V with respect to z0. t Manuscript received by the Editor August 23, 1971; revised manuscript received August 1, 1973. * Scripps Institution of Oceanography, Lajolla, CA 92037; formerly with NOAA Atlantic Oceanographic and Meteorological Labs., Miami, Fla. 33149. i University of Washington, Seattle, Wash. Q8105. © 1974 Society of Exploration Geophysicists. AU rights reserved. 33 88: 34 Dorman and Lewis V,(x0, z0) = dV(x0, z0) dZn • f m i -r-AdzPx /- /•» /•*'(*)' (z-z0)dzd2x -w^-x^O [|X— Zo (2) = 2irpgz0 Pg j —00 v — 0 |2+(z-z0)2]1/2 (3) d2x [|x-Xo|2+(A(x)-zo)2j1/2 The first term is the Bouguer plate field and the second is the terrain field. The integral, being nonlinear in all of its arguments, is analytically and numerically intractable as it stands, so we seek a series approximation. This integral is a nonlinear functional; i.e., a function which depends upon the function /;(x). Vol terra (1929, 1959) developed a power series expansion for general functional for the solution of certain nonlinear integro-differential equations encountered in the study of populations. A sim- ilar expansion, using orthogonal functions, was used by Wiener (1958) for the simulation of a nonlinear "black box" in communication theory. Barrett (1963) gives a systematic and readable development of the idea. The expansion itself is quite similar to the Taylor series. The general form is f(y, 0 - k0 + j Wh, t')y{h)dh + J J h(h, h, WyitdyQddttdtt (4) + JJ j h(tuh,h,t')y{h),y(h), •yOJdtidhdt, + • • • . When we expand the integral in equation (3) about some average elevation of the topography zav we obtain l'(Xo, Zo) = — 2wpg(zav — zo) + j *i(x0 - x') (A(x') - z„)dx' (5) + f k,(Xo - X')(A(X) ~ Zav)2 'MX 2tX* 2^X1X0 2iri\x i*r i*i ' m *Vt "mii ' in 2 2TXxXy 2ir\v 2iriXy \n ' 1*1 ' m **i ' v*i "** 2vi\x, 2iri\Ut 2x \ X j g-lr\\\Ah Vertical continuation by Ah. Here, X* and X„ are the components of X corre- kt(x + y3)h(x3)dx3 I h2(x + y — x4)A2(*4) ^ 15 10 Root mean square terrain correction fc* Vzz vs root mean square terrain relief /flight elev Density = 2 0 Increasing terrain relief Increasing flight elev _1_ _L _L J_ J_ _L 1 J_ 0 0 02 0 04 0 06 0 08 0 10 RMS TERRAIN RE LIEF/ FLIGHT ELEV. (ABOVE MEAN) I-'lG. 1 . Root-mean -square terrain effect for I\.. as a function of rms terrain relief around mean observation eleva- tion above mean terrain. These calculations were made for Rocky Mountain topographs with an assumed densitv of 2.0. 20 PLANE OF OBSERVATION 0 - -20 -40 - -60 - P=l 0 ^r - 300 "> - 200 ioo 2 < > EXACT LINEAR APPROXIMATION QUADRATIC APPROXIMATION 200 400 600 800 METERS fit. 2. The terrain correction for a two-dimensional trapezoidal riduc calculated l>_\ .i linear approximation, quadratic approximation and exact I \ The nu merit al approximations were i omputed lor a three dimensional huh lei w nh a grid spacing of .50 m. 886 Terrain Effect Calculation 37 •h(x3)h2(x2)dxidx3 + ff k2(x - x2)*2(x + y - x4) • h2(x2)hi(xi)dXidx4. Taking the first of the preceding integrals as an example, we change variables setting Xi = Xi — X, Xa = x3 — x — y t(x)((x + y) = j j H-xl)U-xi)h{xl + x) ■h(xi +x + y)dx{dx£ + • • • Now the autocorrelation of t(x), Rtt(y), is obtained by averaging /(x)*(x+y) over all possible values of x so, ru(y) = J"*i(-xi')*i(-x,') •rhh(xz + y — Xi)dx(dxi + • • • In the wavenumber domain, including the other terms, we get for the power spectrum of the ter- rain effect. Rtt = pgiK.RnH + 2KiK2Rhh* + KiRh'h> + •••], where R^ is the power spectrum of the topog- raphy, Rhh* is the cross-power spectrum of the topography and its square, and RhW is the power spectrum of the square of the topography. EXAMPLE The rms terrain effect can be used as a crude indicator of the magnitude (and hence accuracy) of the corrections required. It is a conservative estimator since it includes all wavelength com- ponents, some of which (the very long ones) would be removed by filtering. The rms terrain effect is simply the square root of ru(0), the value of the autocorrelation function for an argument of zero lag. We have computed the rms terrain effect for vZz, the second vertical derivative of the potential from some digitized topography provided by the Union Oil Co. of California. The area digitized is a 15-minute quadrangle in the Rocky Mountain area. The grid interval was about 300 m. The total relief in the quad is 550 m, so the terrain is moderately rugged. The power spectrum falls off like 1/|a|17. For this computation we assumed that the topography is isotropic although in fact there are linear trends. This reduces the terrain effect some- what since the field from a linear object decays less slowly with distance than one with radial symmetry (see Hammer, 1971). The density as- sumed was 2.0 g/cms. The results are presented in Figure 1 in terms of the dimensionless ratio rms terrain relief/flight elevation above mean. From this calculation we see that when the rms terrain is only 2| percent of the flight elevation, we still have a terrain effect of 5 Eotvos, so terrain corrections will play a more important role in gradiometry than in gravimetry. To check this calculation, we computed the rms terrain effect for the ratio 0.10 by direct integration using equation (3) and found agree- ment. Another example Chinnery (1961) has computed coefficients for the graphical calculation of the terrain corrections for V„ and compares the exact and graphical solutions for a two-dimensional trapezoidal ridge. Figure 2 shows such a comparison for the expan- sion method. The accuracy of the expansion method appears to be greater than that of the graphical method. ACKNOWLEDGMENTS • This work was supported in part by Atlantic Richfield Co., Mobil Research and Development Corp., Pan American Petroleum Co., and Union Oil Co. of California. We thank J. W. Lavelle for reading this manu- script and Sigmund Hammer for reading a previ- ous version. REFERENCES Barrett, J. F., 1963, The use of functional in the anal- ysis of non-linear physical systems: J. Electr. and Control, v. 15, p 467-574. Bott, M. H. P., 1959, The use of electronic digital com- puters for the evaluation of gravimetric terrain cor- rections: Geophys. Prosp., v. 7, p. 45-54. Chinnery, M. A., 1961, Terrain corrections for airborne gTavity gradient measurements: Geophysics, v. 26, p. 480-489. Dean, William C, 1958, Frequency analysis for gravity 887 38 Dorman and Lewis and magnetic interpretation: Geophysics, v. 23, p. Lewis, Brian T. R., and Dorman, LeRoy, 1970, txnen 87-127. mental isostasy 2: An isostatic model for the I'S A Dorman, LeRoy M., and Lewis, Brian T. R., 1970, derived from gravity and tonograpbic data: J. Gen Experimental isostasy 1 : Theory of the determina- phys. Res., v. 75, p. 3367-3386. tion of the earth's isostatic response to a concen- parker. R. L., 1973, The rapid calculation of potential trated load: J. Geophys. Res., v. 75, p. 3357-3363. anomalies: Geophvs. J. R. Astr. Soc, v. 31, p. 447- Evjen, H. M., 1936, The place of the vertical gradient in 455 127-136i0nal interpretati°ns: Ge°Physics> v- l> P- Schwartz, L., 1966, Mathematics for the physical Sci- Hammer, ' Sigmund, 1971, Vertical attenuation of ences: Hermann, Paris, 358 p. anomalies in airborne gravimetry: Geophysics, v. 36, Volterra, V., 1929, 1959, Theory of functional and of p. 867-877. integral and integro-dinerential equations 266 p., Kaiie, M. F.,' 1962, A comprehensive system of terrain 1929> Blackie, London: 1959, Dover, N. Y. corrections using a digital computer: Geophysics, v. Wiener, N., 1958, Non-linear problems in random 27, p. 455-462. theory: MIT Press, Cambridge, 133 p. 888 fS® AlMOs^ rMENJ OV U.S. DEPARTMENT OF COMMERCE Frederick B. Dent, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator ENVIRONMENTAL RESEARCH LABORATORIES Wilmot N. Hess, Director NOAA TECHNICAL REPORT ERL 318-MESA 1 Suspended Particulate Matter in the New York Bight Apex: September-November 1973 DAVID E. DRAKE BOULDER, COLO. November 1974 For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402 889 DISCLAIMER The NOAA Environmental Research Laboratories do not approve , recommend , or endorse any proprietary pro- duct or proprietary material mentioned in this publi- cation. No reference shall be made to the NOAA Environmental Research Laboratories , or to this publication furnished by the NOAA Environmental Research Laboratories , in any advertising or sales promotion which would indicate or imply that the NOAA Environmental Research Laboratories approve, recommend, or endorse any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indi- rectly the advertised product to be used or purchased because of this NOAA Environmental Research Labora- tories publication. 890 CONTENTS Page ABSTRACT 1 1. INTRODUCTION 2 2. FIELD AND LABORATORY METHODS 4 3. RESULTS V 3.1 Suspended Sediment Distribution 7 4. DISCUSSION 30 4.1 Suspended Sediment and Advective Currents 30 4.2 Suspended Sediment Textures 34 4 . 3 Suspended Sediment Transport and Bottom Sediment Distribution 37 5 . SUMMARY 44 6. ACKNOWLEDGMENTS 45 7. REFERENCES 46 APPENDIX. SUSPENDED SOLIDS DATA 50 891 SUSPENDED PARTICULATE MATTER IN THE NEW YORK BIGHT APEX: SEPTEMBER-NOVEMBER 1973 David E. Drake ABSTRACT The distribution of suspended particulate matter in the New York Bight apex was studied during the fall of 1973 as part of the Marine Ecosystems Analysis program of NOAA. Five surveys from September through November revealed consistent suspended matter distributions that reflect the bight apex water circu- lation. Two major currents dominate during the fall season of limited river flow and gradually weakening water column stratification: (1) relatively fresh surface water, containing between 1 to 4 m.g/1 of suspended particles , flows from Hudson estuary and down the New Jersey coast within 5 to 10 km from shore; and (2) northward flow along Hudson shelf channel occurred during all surveys. Low concentrations of suspended matter and ashed-weight fractions dominated by diatoms indicate a central shelf origin for the shelf-channel current. Surface winds have a strong influence on the currents at all depths in the bight apex. During the fall season, winds are predominantly from western quadrants and tend to sweep through upwelling and northward flow along Hudson shelf channel. Current meter records appear to show that the shelf channel flow waxes and wanes in response to the strength and direction Of surface winds. Total suspended matter distributions and dispersion patterns of iron particles dumped at the acid-waste dumpsite support the existence of a clockwise gyre in the central portion of the area during the fall season; the shelf -channel current forms the western limb of this gyre. Dredge spoil and sewage sludge dumped near the head of the shelf channel settle within the shelf channel to form organic-rich mud lenses. How- ever, some of this material is entrained by the northward valley current and transported from the shelf channel to the northeast over Cholera Bank. The bank crest does not accumulate fine sediment owing to rela- tively vigorous wave surge. However, as the turbid current turns south along the east side of Cholera Bank, fine-grained, organic-rich mate- rial begins to settle. The result is two disconnected lenses of organic- rich sediment on either side of the sand bank. Contaminated sediments are widely dispersed in the bight apex water column. However, major dispersion appears to be centered on the Hudson shelf channel with good evidence that material dumped at the valley head is transported both up and down the channel in substantial quantities. 892 One of our surveys coincided with a moderate storm which pro- duced steep, 1.0- to 3.0-m seas. Resuspension of clay and silt-sized material occurred throughout the area, and, owing to the near absence of water column stratification, this sediment was rapidly mixed toward the sea surface. A minimum of 10 4 metric tons of sediment was entrained during this storm, and it is clear that such high energy events strongly influence the fate of natural and artificial sediments in the New York Bight . 1. INTRODUCTION Five surveys of a standard station grid were completed in fall 1973 in the apex of the New. York Bight (fig. 1). The surveys included a wide variety of observations designed to define physical and chemical water property distributions and controlling processes. Suspended par- ticulate matter was among the properties investigated, and the results form the basis for this NOAA Report. The work reported in this report is the beginning of a study of man's impact on the ecology of the continental shelf between Montauk Point, N.Y. , and Cape May, N.J. Initial emphasis is being directed toward the shallow shelf off the Hudson estuary because this area annually receives approximately 4.6 x 10 6 tons of dredge spoils, sewage sludge, industrial wastes, and other waste products (Gross, 1972). Because of this dumping, sizable areas of the sea floor in the apex (principally near the sewage dumpsite) have been shown to be nearly devoid of marine life (Pearce, 1970). The degradation of the immediate coastal environment and the real possibility that the pollutants or their effects may spread to other areas emphasize the importance of gaining a complete understanding of the transport of both natural fine 893 Figure 1. View York Bight apex. Stations are numbered solid circles (1-25). Major dumpsites are designated as follows: DS, dredge spoil; SS, sewage sludge; AW} acid waste; and CD3 cellar dirt. Bathymetry is in fathoms. 894 sediments and artificial contaminants. The bulk of the demonstrably toxic pollutants (contained in dredge spoil and sewage sludge) can be expected to move predominantly as suspended load — either as discrete particles or adsorbed to the surfaces of other grains. 2. FIELD AND LABORATORY METHODS Surveys of the 25 stations (fig. 1) were scheduled to bracket Earth Resources Technology Satellite (ERTS-1) satellite overpasses. The dates of these surveys were: August 27-31, September 16-19, October 1-4, November 4-9, and November 26-30, 1973. For convenience, they will be referred to as surveys 1 through 5 in this NOAA Report. Complete lists of the measurements obtained on each cruise are available from the National Oceanographic Data Center. Discussion of the distri- butions of temperature, salinity, dissolved oxygen, inorganic nutrients, current meter measurements , and satellite imagery data are being pre- pared by R. Charnell and his colleagues at the Atlantic Oceanographic and Meteorological Laboratories (AOML) . Particulate material retained by glass- fiber filters has been analyzed for carbohydrate and protein content by P. Hatcher of AOML. In addition, Hatcher has studied these constituents along with the total organic carbon content of surficial bottom sediments. His work will be the subject of a separate NOAA Report . Water samples for filtration through Nuolepove (0.45u average pore diameter) and glass-fiber filters were obtained at the surface and at 10-m intervals down to approximately 2 m from the bottom using a 895 submersible pumping system incorporated in an Interocean Conductivity- Salinity-Temperature-Depth unit. The pumping system was not used on the last survey (survey 5) because it was determined that samples were contaminated for metal analyses and the particulate matter was under- going textural changes. The 10- I Niskin Polyvinyl Chloride water samplers were used on the last survey; one bottle was modified at close to 2 m above the sea floor when a leaded line touched bottom. Water samples were transferred immediately to l-l plastic bottles and filtered by vacuum through preweighed Nualepore 47-mm discs for particulate gravimetric analyses, ash-weight determinations, and microscope study. Previous work has shown that these filters are very stable so that control filters were not used. The filters were freed of salt by multiple washings with 25 to 50 ml of distilled water. Particle con- centrations ranged from about 0.1 to 12 mg/ I; volumes processed ranged from 0.3 to 2 I, and the filters were weighed to 0.01 mg in our shore laboratory. All data are reported as weight/ I, All filters were inspected for particulate contaminants with a petrographic microscope , but , owing to time limitations , only samples from the second and fifth surveys were studied for texture (samples not collected with the pump system) . Temperature and salinity profiles through the fall season show the expected change from strong density stratification during early surveys to very weak stratification in late November. Vertical mixing in late November was accelerated by the passage of a storm front which produced 30-kt winds and steep 1.0- to 3.0-m seas from the south. All earlier surveys were blessed with 896 relatively fair weather; thus, the late November data provide an oppor- tunity to evaluate the effects of a moderate storm. Tentatively, we assume that suspended particle distributions during the second and fifth surveys are representative of late summer and early winter con- ditions , respectively. Particles to 4 urn could be resolved with standard light micro- scopy; however, size measurement could be done with confidence only on grains > 10 urn. Intermediate diameters were measured and converted to equivalent spherical volumes for each Wentworth size-class. The accuracy of this method is low, but results should be internally con- sistent. Mineral grains were identified by their strong birefringence under polarized light; identification of mineral type was possible only in those few samples containing coarse silt and fine sand. Because biogenic particles are very difficult to size properly, only terri- genous material (birefringent) was studied for texture (see Bond and Meade, 1966). Future surveys will employ a Coulter Counter for size analyses . The weight loss following ashing in air at 500°C was taken as a measure of total organic matter; the error involved in loss of water bound by clay minerals was neglected (Manheim et al.3 1970). The non- combustible ash is a mixture of inorganic and biogenic minerals (amorphous silica from plankton). 897 3 . RESULTS 3 . 1 Suspended Sediment Distribution Figures 2 through 4 present the areal distributions of total sus- pended particulate matter (SPM) at the sea surface, at 10 m, and at 20 m during fall 1973. Near-bottom concentrations determined with the bottom- tripping Niskin bottle during survey 5 are shown in figure 4d. Early results, using the pumping system near the sea floor, are questionable because of the steep vertical gradients in SPM and the lack of precise positioning of the pump head above the sediment surface. Benthic layer sampling can be meaningful only if samples are precisely located above the seabed by divers or bottom- tripping devices. SPM values are com- piled, according to survey and depth, in the appendix; average concen- trations (all surveys) are shown for each station and sampling level, and these "season averages" are plotted in figures 5a and 5b. The sub- stantial increase in SPM at most stations during the last survey (which was affected by the storm) is particularly evident in the appendix. Combustible and ash fractions of the suspended matter for the third survey and textural data for the second and fifth surveys are pre- sented in figures 6 , 7 , and 8 . Without chemical analyses , identification of most suspended pollutants is difficult or impossible. For example, even at stations within a few kilometers of designated sewage and dredge spoil sites , particles unquestionably derived from these sources cannot be separated with standard light microscopy. Inorganic and organic chemical investigations are in progress under the direction of 898 (a) 40*20^ (b) Figure 2. (a) Suspended particulate matter (mg/l) in the surface water 3 Sept. 16-19 3 1973; and (b) suspended particulate matter (mg/l) in the surface water, Oct. 1-4, 1973. 899 (a) 40*20' N 74*00 W (d) 74*00'w Figure 2. (c) Suspended particulate matter (mg/l) in the surface water, Nov. 5-9, 1973; and (d) suspended particulate matter (mg/l) in the surface water, Nov. 26-29, 1973. 900 (a) — 40°30 N (b) Figure 3. (a) Suspended particulate matter (mg/l) at a depth of 10 m3 Sept. 16-19, 1973; and (b) suspended particulate matter (mg/l) at a depth of 10 m3 Oct. l-43 1973. 901 (c) — t0°30 N (d) TA'OO'W Figure 3. (a) Suspended particulate matter (mg/l) at a depth of 10 m3 Nov. 5-93 1973; and (d) suspended par- ticulate matter (mg/l) at a depth of 10 m3 Nov. 26-29 3 1973. 902 (a) (b) Figure 4. (a) Suspended particulate matter (mg/l) at a depth of 20 m3 Sept. 16-19, 1973; and (b) suspended particulate matter (mg/l) at a depth of 20 m3 Oct. 1-4, 1973. 903 (e) KILOMETERS (d) 4O°20'N Figure 4. (o) Suspended particulate matter (mg/l) at a depth of 20 m, Nov. 5-9, 1973; and (d) suspended par- ticulate matter (mg/l) 2 m over the sea floor, Nov. 26-29, 1973. 904 (a) — 40°30 N (b) Figure 5. (a) Computed averages of suspended particulate matter (mg/l) in the surface water for all surveys; and (b) oomputed averages of suspended particulate matter (mg/l) at 10 m for all surveys. 905 (a) 0 12 3 4 5 KILOMETERS / / / L L (b) Figure 6. (a) Noncombustible fraction of suspended mat- ter in surface waters during Oct. 1-4 , 197 3 3 in mg/l; and (b) combustible fraction of suspended matter in sur- face waters during Oct. 1-4 , 1973, in mg/l. 906 (c) 40 33 45 68 40 52 39 16 — (d) 75 62 51 63 53 76 39? 68 — 40°30 N Figure 6. (c) Noncombustible fraction of suspended mat- ter in surface waters during Oct. 1-4, 1973, expressed as a percentage of the total suspended solids; and (d) noncombustible fraction of suspended matter near the sea floor during Oct. 1-4 s 197 3 3 as a percentage of the total suspended solids. 907 (a) (b) — 10°30 N Figure 7. (a) Size distributions of mineral grains sus- pended in surface waters during Nov. 26-29 3 1973; and (b) size distributions of mineral grains suspended 2 m over the bottom during Nov. 26-29, 1973. 908 Figure 8. Texture of mineral grains suspended in surface waters during Sept. 16-19 3 1973. 909 D. Segar and P. Hatcher of AOML and will be reported elsewhere. These studies should improve our knowledge of pollutant distribution and transport. Nevertheless, much can be learned concerning dispersal of suspended solids through studies of contaminants which can be readily identified and quantitatively measured under the microscope. Two such materials are common in the bight apex: yellow to orange-red iron hydroxide ( ? ) and iron-stained plankton particles formed after dumping of iron-rich, dilute acid wastes in the southeast section of the area (fig. 1); and black soot grains which are most likely derived from the heavy ship traffic in the harbor and its approaches (Manheim et al., 1970). Because the iron particles essentially originate at a point and are readily identified on membrane filters , they provide an excellent tracer for advective current patterns. In uncontaminated ocean water, most iron is in the form of parti- culate iron compounds ranging from 2 to 20 ug/Z- (Sverdrup et al., 1942; Lewis and Goldberg, 1954; Riley and Chester, 1971). Soluble iron carried by rivers is precipitated in saline waters owing to increases in ionic strength and pH (Aston and Chester, 1973). Similar reactions occur in the wake of the barges which dispose of the iron-rich, dilute acid industrial wastes in the bight. Gross (1972) estimated that about 800 tons of solid material are dumped at the acid-waste site every day (compared to - 80 tons/day when this practice began in 1948; Ketchum et al., 1951). Ketchum and his colleagues (1951) estimated the iron contribution from Hudson estuary as 40 to 50 tons /day; however, this estimate was made just after National Lead Company changed its dumpsite 910 from the Raritan River (inside Hudson estuary) to the present offshore area. Consequently, it is likely that its data reflected the continu- ing "washing out" of sedimented iron from the estuary and river. During our field work, particulate iron particles, which were large enough to be counted under the microscope, averaged < 3/mm2 of filter surface (3,000/Z) near Hudson estuary. Thus, grain counts exceeding 3/mm2 are considered to be indicative of material from the dumpsite. Generally, it is possible to determine the origin of iron particles using the grain-count distribution patterns. The iron particles range in size from colloidal, yellow, filter coatings to sand-sized (> 62 urn) orange and red aggregates having the appearance of floccules of finer grains. X-ray diffractograms show no evidence for crystalline structure. Although this may result from the colloidal particle sizes and poor crystallinity , there is reason to believe that the orange and red grains are a mixture of hydrated iron oxide and iron-stained phytoplankton . In fact, the wide dispersal of this material in the bight supports the idea that some of it is low- density, easily transported plankton. Figures 9 and 10 present the distribution of these particles derived from counts of the number of grains between 10 and 62 urn on 1 mm2 of filter surface. In general, surface and mid-water samples near the acid-waste dumpsite contained a wide range of sizes from unresolvable colloidal material to medium silt. Concentrations near the bottom were typically higher (fig. 9 and 10) and coarser grained with some particles well into the very fine sand range. The trend toward coarser texture 911 (a) . 1-4, 1973. Val- ues are in numbers of grains per mm of filter surface. 912 (a) -~ 40°30 N 74°00'W (b) Figure 10. (a) Iron particles in surface waters during Nov. 26-29, 1973; and (b) iron particles at a depth of 10 m during Nov. 26-29, 1973. 913 (a) Figure 10c. Iron particles 2 m over the bottom during Nov. 26-29, 1973. 914 (and high grain counts) was particularly evident in near-bottom samples from the Hudson shelf channel in late November (stations 18 and 13; fig. 10). Opaque , subspherical black grains and grain aggregates , ranging in size from fine silt to very fine sand are a common minor constituent of samples in the bight apex (Manheim et at., 1970). In our samples, the black grains comprise less than 1 percent of the total SPM, but tend to be consistently more abundant in the turbid plume emanating from the Hudson estuary and flowing south along the New Jersey coast (fig. 11). Figure 11a shows a rather high count of black grains at station 13, only 3 km from the sewage dumpsite. These grains may be related to sewage disposal, but optically they are not obviously different from the black soot. Whereas Manheim and his colleagues (1970) found processed cellulose fibers in several samples near New York, we have found this material in less than 1 percent of our samples. As their sampling was completed in the summer of 1966, the difference may be seasonal. How- ever, it seems more likely that the few samples which they recovered coincidentally hit "patches" of heavily contaminated surface water. Figure 12 presents representative examples of the vertical distribution of SPM throughout the fall season. The vertical profiles reflect the seasonal breakdown of temperature and salinity stratifi- cation. In early September, both temperature and salinity contribute to a stable stratification with a distinct, steep-gradient pycnocline between 15 and 25 m (fig. 13); the pycnocline tends to shoal toward 915 (a) (b) •wzo'n Figure 11. (a) Opaque black grains in surface waters dur- ing Nov. 26-29 s 1973. Values are in number of grains per mm of filter surface. (b) Opaque black grains 2 m over the bottom during Nov. 26-29, 1973. Values in no. /mm of filter. 916 Oi- WSC-2 (SEPTEMBER 1973) it 12 13 14 15 20 (a) 4oL 1000 500 1000 2000 30Q0_ , 77777f7T7777Tjjyyy WSC-3 (OCTOBER 1973) (b) 40L 15 7777777777777777777777777$ WSC-4 (NOVEMBER 1973) 11 12 13 14 15 20 (c) 40L 2000 1000 3000 7777777777777777777 (d) WSC-5 (NOVEMBER 1973) 15 177777777777777777777 Figure 12. Cross sections of suspended par- ticulate matter (in mg/l) through stations 11-15 for: (a) Sept. 16-19; (b) Oct. 1-4; (c) Nov. 5-9; and (d) Nov. 26-29, 1973. See figure 1 for station locations. 917 (a) TURB 55 60 65 70 75 80 85 90 95 100 5 1 1 1 1 1 L 1 1 - 10 - - £ 15 LI t- UJ 5 20 - 25 - T(°C) J 1.0 mg/Z to mark arbitrarily the seaward limit of this current, it averaged 4 to 6 km in width. (2) A sharp decline in SPM and a marked composition change occur in moving from the Hudson "plume" to the east. In fact, the lowest SPM concentrations in the area are commonly present over the north- to south- trending Hudson shelf channel (see fig. 2 through 5). Samples above the channel contain numerous diatoms which are common over the middle shelf, and Hatcher (personal communication, 1974) has found that these samples are rich in high protein phytoplankton . In addition, the water within the channel is often colder than water at the same depths elsewhere in the area. These data demonstrate a northward (upslope) flow of water from offshore along the Hudson shelf channel, although it is not yet certain to what degree this current is confined to the chan- nel. When meteorological conditions are appropriate (strong westerly or northwesterly winds ) , this current reaches the sea surface and may extend north to within at least 5 km of Long Island (see fig. 2a). Studies of the currents within submarine canyons on the Pacific coast of the United States have shown that they periodically reverse in response to tides and perhaps internal waves (Shepard and Marshall, 1969; 1973). Usually a net drift of the bottom water is superimposed on the oscillatory currents. In most canyons studied, the drift averages a few cm/s and is decidedly down canyon. The current oscillations occur with periods ranging from minutes to 6 to 8 hr, and speeds are typically 923 between a few and 50 cm/s. Consequently, fine sediment maintained in suspension by the high speed events is slowly moved down canyon by the net drift (Drake and Gorsline, 1973). G.H. Keller and F.P. Shepard have recently collected long current recordings in Hudson Canyon seaward of the continental shelf break, and these show similar reversing flows. The calculations of net down-canyon drift are not yet available. Within the Hudson shelf channel (that portion of the system incising the shelf), J.W. Lavelle and G.H. Keller of AOML made one 11-day recording 1 m off the bottom at a depth of 62 m (- 6 km south of our study area). This record reveals that the shelf channel orientation controls the direc- tion of near-bottom currents which are driven by both tides and surface winds. Extended periods of flow up or down the shelf channel were clearly related to wind direction and to the initiation of hydraulic currents. Up-channel flow occurred when surface winds swept water above the summer pycnocline seaward, whereas winds producing an onshore pile- up of water caused flow down the channel (Lavelle, personal communica- tion, 1974). Both trace metal (Carmody et at. 3 1973) and organic analy- ses (Hatcher, in preparation) show movement of contaminated sediment down Hudson shelf channel. On the other hand, suspended sediment data presented in this report reflect up-channel transport in the bight apex. Considerably more current measurements are needed to determine the degree to which surface winds and channel-currents are coupled, parti- cularly, the seasonal variations in the system. Nevertheless, it is apparent that sediment dispersal along the channel both to the north 924 and south is an ongoing process. Material dumped into this topographic low will be widely dispersed, and contaminants will be exported to areas far removed from the dumpsites. (3) Figures 9 and 10 show that the Hudson shelf-channel current turns to the east-northeast following the configuration of the broad channel head. Eastward flow appears to occur subparallel to the shelf bottom contours between the depths of 10 and 20 m. The current, there- fore, flows over the shoreward end of Cholera Bank. The fate of this flow is not clear. During all surveys, a particle-rich plume was pre- sent, trending south along the eastern margin of our area (fig. 2a, 4, and 5). As discussed earlier, this plume is easily recognized on ERTS-1 images and resembles an enormous rip current. This geometry suggests a southward deflection of the eastward current along the east flank of Cholera Bank. The circulation system described above is completely supported by the dispersal pattern of iron hydroxide and iron-stained grains (fig. 9 and 10). In particular, data from the fifth survey suggest the degree to which the circulation is topographically controlled. 4 . 2 Suspended Sediment Textures The size distribution of inorganic mineral grains in suspension was determined for the fifth survey and for the surface samples taken during the second survey ( fig . 7 ) . Inorganic minerals typically make up 25 to 50 percent (by volume) of the total suspended matter close to 925 shore and near the bottom. In the seaward portions of the apex and within clear waters from the central shelf, the mineral content is from below 5 to 10 percent. During the earlier of the two cruises, the suspended sediment was predominantly fine silt and clay with < 10 percent of the particles larger than 16 ym. The material counted as > 16 urn was, in nearly all cases , aggregates of many smaller grains bound together by amorphous organic matter. Although the microscope technique contributes to the apparent areal uniformity of the size distributions, it is clear that the texture of the mineral matter during September was similar at all stations. The predominance of < 8-ym material supports the suggestion that larger particles are either trapped inside the estuary or settle rapidly near the estuary mouth. The November surface-water data show a significant coarsening of the suspended solids which we attribute to the addition of material from bottom resuspension. Nevertheless, most samples are predominantly com- posed of < 16-um particles. Near the sea floor, the addition of mica, quartz, and grain aggregates in the silt-to-sand sizes was particularly evident over Cholera Bank and along the east wall of the Hudson shelf channel . The sediment carried by the Hudson estuary plume along the New Jersey coast is texturally distinctive. Even the near-bottom suspen- sions are predominantly < 16 urn and generally become finer grained toward the south; this trend is well shown in the surface water samples (fig. 7). Except for samples near the sea floor, suspended particles 926 larger than 16 urn are rarely single grains . Thus , the textural change which occurs as the Hudson plume moves southward is probably the result of the settling of large aggregates and agglomerates of organic and inorganic clay and very fine silt from the surface layer. These results are in agreement with the large body of data which show that Atlantic coastal plain estuaries are efficient sediment traps (see Meade, 1969; 1972). Salt balance considerations, direct current measurements, sil- tation studies , and bottom drifter surveys demonstrate landward flow of near-bottom, saline water into estuaries (Harrison et al.s 1967; Meade, 1969). Because reduced salinity surface water extends over the inner shelf, an "extended" estuarine-like circulation is typically developed within a few kilometers of estuary mouths (Gross et at., 1969). Therefore, while estuary-mouth tidal currents are strong and mix coarse material into surface layers, this material settles back into the landward- f lowing , saline bottom water within a few kilometers seaward of the estuary. Thus, only the finest sediment (< 8 urn) which moves with the surface water and escapes inclusion in grain aggregates can avoid transport into the estuaries along the coast. Detailed investigation of the concentrations, composition, and settling rates of aggregates is planned. Our initial observations indicate that aggregates and fecal pellets are particularly abundant in the estuary mouth and along the transition zone between turbid coastal water and clearer open-shelf waters. Manheim et at. (1972) observed sJJTiilar aggregate distributions in the Gulf of Mexico. Our future work 927 will include Coulter Counter particle-size analyses. At the present time, we do not have sufficient data to draw firm conclusions regarding the regional patterns of suspensate texture. 4 . 3 Suspended Sediment Transport and Bottom Sediment Distribution Recent research on shallow marine sedimentation has emphasized the difference between processes occurring during fair weather and storm conditions (Swift, 1970; Smith and Hopkins, 1972; Drake et al., 1972; Rodolfo et at. j 1971; Sternberg and McManus , 1972). Undoubtedly, sedi- mentation at the shallow depths in the bight apex (mostly < 30 m) is very strongly influenced by winter storms. Owing to the weak density stratification in the winter, the transfer of wave- and wind-current energy to the bottom should be more efficient (Komar et al. , 1972), and, as shown by the SPM concentrations in late November, the vertical mixing of fine silt and clay sediment is relatively unimpeded. In an attempt to get some idea of how much fine sediment is entrained during storms, this author assumed that the data before our last survey are represen- tative, "fair weather" data (September 16 through November 9). The assumptions involved are that contribution of "new" material from land and plankton production were constants. This is unlikely but our micro- scope analysis of the fall filters indicates that plankton standing crops in September and October were higher than those in November. Thus, the concentration differences (in terms of inorganic components) should, in fact, be greater, and we can take the computed "storm-entrained" amount as a minimal value. The November storm involved high velocity 928 winds (20 to 30 kt), but no coastal precipitation; therefore, we will assume a constant discharge from the Hudson estuary. Using all data for surveys 2 through 5 (September 16 through November 29), the mean differ- ence in SPM for the apex water volume between the early surveys and the fifth survey is approximately 0 . 5 mg/ I . This omits the poorly known concentrations in the near- bottom zone (0 to 5m above bottom) and, therefore, is a conservative estimate. The volume of the bight apex (fig. 1) included within our station grid is roughly 20 km3 which yields a suspended solids "excess" of about 10,000 metric tons in late Novem- ber, assuming a particle density of 2.0 g/cc. Some appreciation of the magnitude of this is gained if it is recalled that one barge load of sewage contains between 100 and 200 metric tons of solid material (on an average day, five barges dump sewage in the bight apex). The amount of material resuspended by more intense storms and longer period waves remains unknown, but it is obvious that winter storms must be of great importance in determining the ultimate fate of all particulate materials in the bight apex. Although winter conditions accelerate sediment transport, our data suggest that under all conditions a near-bottom layer of particle- rich water is characteristic of the area (fig. 12 through 14). In the deep sea, this turbid layer has been termed the "nepheloid layer" (Eittreim et al.3 1969), and it appears to be a fundamental feature of vertical profiles of SPM over continental shelves (Spencer and Sachs, 1970; Drake, 1972; Buss and Rodolfo, 1972; Lisitsin, 1972). The particles in this zone are usually mostly noncombustible , and the 929 terrigenous fraction is slightly-to-markedly coarser grained than near- surface material (fig. 7). SPM concentrations in the nepheloid layer in the bight apex were, with few exceptions, as high or higher than at any other level in the water column. Observations of the Middle Atlantic Coastal Fisheries Center (1972) and ERTS-1 satellite imagery data (Charnell et al.3 1974) showed that surface turbidity increases resulting from sewage dumping and dredge spoiling may extend for several square kilometers to tens of kilometers around the dumpsites. Our data do not show any large in- creases in surface SPM near either site, but this probably is a function of our wide station spacing. In the future, we will conduct very detailed investigations of both dumping operations to determine: (1) the proportions of floating and rapidly settling materials ; ( 2 ) the particle settling rates; and (3) the areal extent of impact. At the present time, we tentatively expect that most of the dumped material settles to the near-bottom zone within a few kilometers of each site. This does not mean that all, or even a large part, of a given barge load deposits on the bottom, but rather, it may be dispersed largely within the nepheloid layer. The distribution of suspended solids near the bottom in late November tends to support this conclusion (fig. 4d). Concentrations ranged from 0.91 to 5.5 mg/Z, with most of the higher values (> 2 mg/Z) present near the estuary and beneath the Hudson turbid plume. However, it is noteworthy that the highest concentrations beyond 5 km from shore were present near the dredge spoil and sewage sludge dumpsites. These highs are generally surrounded by a large area of 930 turbid water containing more than 3 . 5 mg/ I of SPM which apparently extends into the Hudson estuary. In addition, a band of relatively high particle concentrations was present trending eastward over Cholera Bank from the main sludge bed in agreement with the circulation pattern discussed earlier. Charnell et at. (1972) have suggested that a part of the bottom water moving north along Hudson shelf channel continues into the estuary, whereas the data discussed here demonstrate transport out of the valley head to the east-northeast. These conclusions are not in conflict, but are a logical consequence of the "extended" shelf -estuarine circulation (Charnell et al.} 1972; Gross et al.3 1969; Harrison et al.s 1967) and the clockwise central-apex gyre (Charnell et al.3 1972; and this report ) . The implications of what has been learned from our study of one season in the bight apex are: (1) Future investigations of pollutant transport should focus on physical and chemical processes within 10 m of the sea floor. (2) Iron particles formed following chemical waste disposal are an excellent current tracer. Dispersal of this material from the south- eastern part of the area follows current patterns indicated by SPM distributions and is recently supported by direct current -meter measure- ments (Charnell, personal communication, 1974). Of particular signi- ficance is the wide dispersal of silt-sized iron particles found in the nepheloid layer in October 1973 (fig. 9). Although the method of 931 disposal of the iron-rich acid (pumping from a moving barge) undoubtedly contributes to this wide dispersal, it also is evident that no part of the bight apex which we have sampled is free of contamination. (3) The dredge spoil and sewage dumpsites are located on either side of the Hudson shelf channel head, apparently within a current with a net northward flow during the fall season. As shown in figure 2a, this current at times can be traced as far north as 5 km from the Long Island coast where our stations start; it is probable that the current is closer to the shore than 5 km. However, this current appears more often to turn to the east as it flows out of the shelf channel. During November 1973, the pattern was especially well-defined by concentrations of silt and fine sand-sized iron particles (fig. 10). The distribution of "sewage-derived muds," determined from intensive sampling by the Middle Atlantic Coastal Fisheries Center (1972) and by Cok (unpublished data) , strongly suggests that this material is being entrained by the shelf channel current and clockwise gyre (fig. 15). The distribution of organic matter in the bottom sediments reflects initial deposition of sewage and dredge spoil within the amphitheater of the shelf channel . It is noteworthy that Cok (unpublished data) found relatively clean sand immediately below the sewage dumpsite; black, cohesive muds are present several kilometers to the west of this site on the eastern slope of the shelf channel. The thickness of these black muds is thought to be less than 1.5 m, based on 3.5-KHz profiling and bottom sampling (Freeland, personal communication, 1974). Unless sewage barges have been con- sistently short-dumping, it is evident that this material is not accumu- 932 Figure 15. Total organic matter in surficial bottom sed- iments of New York Bight (after Middle Atlantic Coastal Fisheries Center 3 1972). lecent work by Hatcher (AOML) has shown that high organic-carbon values extend south from the valley head following the course of Hudson shelf valley. 933 lating on Cholera Bank (beneath the designated dumpsite) , but rather is being swept westward to form a thin but widespread lens of organic-rich sediment . In addition to the channel-head deposit, a second lens of organic- rich silty sand is present on the eastern flank of Cholera Bank (fig. 15). The connection between this deposit and the primary deposit is not well defined, but evidence for a connection has been found in the ratio of carbohydrates to total organic carbon in bottom sediments over Cholera Bank (Hatcher, in preparation) and in our near-bottom SPM data (see fig. 4d and 10). Higher current energies along the crest of Cholera Bank are to be expected, and this is the simplest explanation for the lack of a mud deposit beneath the sewage dumpsite and a clear (textural) connec- tion between the two areas of organic-rich material. Silt and clay entrained from the valley head deposits are moved north and east in the nepheloid layer by the clockwise gyre. These sediments are prevented from settling until the advective current has traversed the sand bank and begun to flow south- southeast into deeper water. The particulate load then settles in topographic lows which afford sufficient protection from wave surge and wind- related currents. (4) Sediments entering the shelf channel also are actively carried to deeper water by downslope bottom currents caused by the pile-up of wind-driven surface water along the Long Island coast (Lavelle, personal communication, 1974) and tide-driven current reversals.. 934 5. SUMMARY Although the results presented in this report cover only a small portion of 1 year and many more analyses on these and other samples remain to be completed, it is possible to advance several important conclusions. Northward flow and possible upwelling along the Hudson shelf channel are indicated by the persistence of relatively particle-free water within and above this topographic low. The "open shelf" water at times reaches close to the Long Island coast, but probably subsequently turns and flows eastward parallel to bottom contours between 10 and 20 m. A portion of this flow probably also moves directly into the Hudson estuary. Although supporting evidence is not strong, there is some justification for a southward turn of the current along the east flank of Cholera Bank to complete a clockwise gyre. Such an advective current geometry would seem to agree with the distribution of organic-rich (sew- age?) muds on the bottom (Middle Atlantic Coastal Fisheries Center, 1972) Major transport of fine particulate load along the New Jersey coast occurs within a surface layer of low salinity water contributed by the Hudson estuary. Textural analyses suggest that much of the coarser material (> 16 urn) and an indeterminate amount of aggregated, finer detritus in this current settle into the near-bottom zone close to the estuary mouth. Formation of organic aggregates containing significant amounts of inorganic mineral matter appears to occur near the mouth of the estuary. 935 In areas not influenced directly by the Hudson turbid plume, the bulk of the transport of detritus takes place in the nepheloid layer. The apparent permanence of this near- bottom, turbid "haze" indicates the importance of current activity and resuspension processes. Our data show that the seasonal breakdown of water column stratification and the passage of winter storms will lead to increased erosion of muds deposited during quieter periods and not yet appreciably compacted. Iron hydroxide and iron-stained particles formed following acid waste disposal in the southeast corner of the area are spread widely by apex currents. If one allows that other waste materials can be dis- persed as easily, the recent discoveries of "sewage sludge" deposits nearly 15 km northeast of the dumpsite and high concentrations of trace metals and organic matter nearly 30-km seaward in the shelf channel should be expected. 6 . ACKNOWLEDGMENTS I gratefully acknowledge the field efforts of P. Hatcher and G. 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(eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsburg, Pa., pp. 225-248. 938 Meade, R.H. (1969): Landward transport of bottom sediments in estuaries of the Atlantic coastal plain, J. Sedimentary Petrology 39:222- 234. Meade, R.H. (1972): Transport and deposition of sediments in estuaries, Geol. Soo. Am. Mem. 133,, pp. 91-120. Meade, R.H. , P.L. Sachs, F.T. Manheim, J.C. Hathaway, and D.W. Spencer (in press): Sources of suspended matter in waters of the Middle Atlantic Bight, J. Sedimentary Petrology. Middle Atlantic Coastal Fisheries Center (1972): The Effects of Waste Disposal in the New York Bight 3 final report to the U.S. Army Corps, of Engineers , National Marine Fisheries Service , Sandy Hook Laboratories, Highlands, N.J. Pearce, J.B. (1970): The Effects of Solid Waste Disposal on Benthic Communities in the New York Bight3 Food and Agricultural Organi- zation of the United Nations Technical Conference on Marine Pollution and its Effects on Living Resources and Fishing, Dec. 9-18, 1970, Rome, Italy, Paper FIR: MP/70/E-99. Riley, J.P. , and R. Chester (1971): Introduction to Marine Chemistry 3 Academic Press, New York and London, 465 pp. Rodolfo, K.S., B.A. Buss, and O.H. Pilkey (1971): Suspended sediment increase due to Hurricane Gerda in continental shelf waters off Cape Lookout, North Carolina, J. Sedimentary Petrology 41:1121- 1125. Shepard, F.P. , and N.F. Marshall (1969): Currents in La Jolla and Scripps submarine canyons, Science 165:177-178. Shepard, F.P., and N.F. Marshall (1973): Currents along the floors of submarine canyons, Am. Assoc. Petroleum Geologists Bull. 57: 244-264. Smith, J.D. , and T.S. Hopkins (1972): Sediment transport on the conti- nental shelf off of Washington and Oregon in light of recent current measurements, In: D.J. P. Swift et at. (eds.), Shelf Sediment Transport: Process and Pattern^ Dowden, Hutchinson and Ross, Inc., Stroudsburg, Pa., pp. 143-180. Spencer, D.W. , and P.L. Sachs (1970): Some aspects of the distribution, chemistry, and mineralogy of suspended matter in the Gulf of Maine, Marine Geol. 9:117-136. 939 Sternberg, R.W. , and D.A. McManus (1972): Implications of sediment dispersal from long-term, bottom- current measurements on the continental shelf of Washington, In: D.J. P. Swift et al. (eds.), Shelf Sediment Transport: Process and Pattern 3 Dowden, Hutchinson and Ross, Inc., Stroudsburg, Pa., pp. 181-194. Sverdrup, H.U., M.W. Johnson, and R.H. Fleming (1942): The Oceans3 Their Physics, Chemistry _, and General Biology 3 Prentice Hall, Inc., New York, N.Y., 1087 pp. Swift, D.J. P. 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COMPARISON OF OPTICAL MEASUREMENTS AND SUSPENDED SOLIDS CONCENTRATIONS IN THE OCEAN DAVID E. DRAKE DOUGLAS A. SEGAR ROBERT L. CHARNELL GEORGE A. MAUL NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION ATLANTIC OCEANOGRAPHIC AND METEOROLOGICAL LABORATORIES 15 RICKENBACKER CAUSEWAY, VIRGINIA KEY MIAMI, FLORIDA 33149 ABSTRACT Beam transmissometers offer a rapid means of deter- mining*" the qualitative distribution of light attenuat- ing materials in the sea. Volume attenuation coefficients and the concentrations of suspended solids show a high degree of covariance. However, due to the variable characteristics of particulate matter and changes in the distribution of dissolved coloring matter, the transmissometer cannot resolve particle concentration changes smaller than about 1 mg/1. Consequently, the application of these instruments in the ocean should be supported with an adequate program of direct water sampling and analysis. INTRODUCTION Although measurements of the optical properties of sea water have been used since the earliest ocean explora- tion for the purpose of investigating suspended matter in the water, such techniques have only recently been widely and intensively applied (Jerlov, 196 8; Eittreim and others, 1969; Carder and others, 1971; Beardsley and others, 1970; Drake, 1972; Kiefer and Austin, 1974; Pak and others, 1970; Zaneveld and others, 1973). 123 945 The use of transmissometers , scattering meters, irradiance meters, and other optical devices has been stimulated by the evolution of marine science toward direct investigation of processes. This new direction is particularly evident in marine sedimentology . Until recently sedimentologists have (in many cases) worked from a knowledge of results back toward a reconstruc- tion of processes leading to those results (see, for example, the discussion by Creager and Sternberg, 1972). Unfortunately, the method lacks resolution, and our crude understanding of present-day processes of sedi- ment transport has become painfully clear, in part because of the pressure arising from environmental problems . Optical measurements have yielded much useful informa- tion and they are especially well suited to process studies over the continental margins (where "synoptic" data collection is critical). Unfortunately, some instruments are being used to measure water properties for which they were not designed, -and some new instru- ments have been marketed that measure nothing more precise than "turbidity." To illustrate some of the limitations on oceanographic use of optical measurements, we present data on the correlations between light transmission measurements, suspended particle concentrations, and satellite imagery off New York and southern California. INSTRUMENTS AND METHODS Light Transmission Light transmission in the sea is principally controlled by scattering and absorption due to the water, suspend- ed solids, and dissolved coloring matter. Transmisso- meters are designed to measure the intensity of image forming light remaining at some distance from the light source. This intensity is generally recorded as the percentage of transmitted light relative to trans- mittance in perfectly clear water (0-100%) . Percent transmission values are converted to the volume atten- uation coefficient (o0 using: 124 946 * = hi — In x where L is the beam length in meters and x is the % transmission (see Jerlov, 1968). Petzold and Austin (1968) briefly outline the design requirements for accurate in_ situ measurement of alpha. Because the absorption and scattering of light by the water and by particulate and dissolved substances are strongly dependent on wavelength, the spectral sensi- tivity of the instrument should be carefully selected and precisely known. In addition, reliable measure- ment of alpha requires that the light due to forward scattering within the beam be minimized. This is accomplished by selecting the smallest beam width-to- length ratio that is compatible with instrument size and electronic limitations. Generally, a ratio of less than 1/50 will reduce forward scatter error to less than 2% in coastal waters (Preisendorfer , 1958) . We have used a 100-cm path transmissometer designed by the Visibility Laboratory of Scripps Institution of Oceanography (Petzold and Sustin, 1968) and a 10-cm path instrument incorporated in an Interocean CSTD system. The 100-cm unit was carefully designed to produce a reasonably accurate measure of in ocean survey work. Our instrument was set up for peak sensitivity at 470 nm, near the region of maximum transmission in clear sea water. On the other hand, no filters are used in the 10-cm unit and, therefore, the sensitivity is more strongly influenced by the energy in the red and near-infrared portions of the spectrum. In fact, the response of this instrument is controlled by the cadmium sulfide photocell which has a rather broad spectral curve from 600 nm to 800 nm with a peak at 725 nm. Transmission is low in the red region and this accounts for the differences between computed ^ for identical samples using these instruments (Figs. 1 and 2) . Because the two instruments are measuring very differ- ent portions of the light spectrum, it is difficult to compare the resulting values for . The 10-cm device 125 947 is strongly influenced by water absorption but should be almost insensitive to absorption by dissolved "yellow" substances. Conversely, the 100-cm unit is most sensitive in the blue-green where absorption by water is least, but the absorption by particulate and dissolved matter is relatively pronounced. Suspended Particulate Matter Concentrations of particles in sea water samples were determined by vacuum filtration through pre-weighed 0.45 m pore size membrane filters. Laboratory tests on standard suspended solids samples show a repro- ducibility of ± 10% (Drake, 1972) using Nuclepore type filters. However, under field conditions replicate samples may differ by as much as 30-50% unless great care is taken to insure representative sampling. Reproducibility of ± 20% should be considered accept- able for gravimetric analyses of suspended solids in marine waters. Satellite Imagery (ERTS-1) The images obtained by the multispectral scanner (MSS) on the first Earth Resources Technology Satellite can be effectively used to study a variety of oceano- graphic phenomena (Charnell and others, 1974). The MSS senses the light reflected in four spectral bands: MSS-4, 0.5-0.6 m; MSS-5, 0.6-0.7 m; MSS-6 , 0.7 - 0.8 m; and MSS-7, 0.8-1.1 m. Because of the wave- length dependence of the transmission characteristics of ocean water, MSS-4 (blue) will sense light which may have penetrated tens of meters into the water, whereas MSS-7 (near infrared) can see reflected energy that penetrated only a few tens of centimeters. Normally the intensity range of reflected energy from the ocean is small relative to the returns from land. In order to obtain more information from the ocean images, the energy is amplified by a process called "contrast stretching" (see Charnell and others-, 1974) . This process can be applied to each MSS band. For comparing environmental data to the remotely sensed ERTS data, it is desirable, in addition to contrast stretching the image, to filter the satellite data to 126 948 eliminate undesired variations and noise and produce first order contours of surface brightness (Maul and others, in press). Such filtering, using a 19 X 19 low pass kerrial, was applied to MSS 5 for both figures 7 and 8. RESULTS Figures 1 and 2 are scatter plots of °Ci qo an(^ °^10 versus concentrations of suspended solids off New York (November 1973) . A similar set of data for ^qq in the coastal waters of southern California is illus- trated in figure 3. Correlation coefficients for each of these curves are about 0.9 (Table 1) demonstrating a strong covariance of and particulate matter. As mentioned earlier, ^io values are higher than c -h c o u nj* T) P, C O fd p •P P. CO w * c o •H P td rH (1) P u o u 3 S u 9 -H E CO 4-> •H • P. X "3" oj id cu g 00 * o + 1 CO o +1 00 o +! en en en oo cti 00 en o en o o CO o uo CO *3* V£> O CO -p x: •H D> C -H 3 CQ E • • o 2 P P •H jC 3 -H o • .r-t — ' c £ u o o 4J to Id o u 03 U T3 id c O • 0 rH C •H o P T3 •H id CD p P T3 id 4-) C rH rH CD CD ■H a P 4-1 CO P 3 0 >1 CO 0 X! rH T3 'O id rH 0 4J 0) c 0 •H •H P 4-1 6 IH s c: u CD -p CD .Q id H3 •H c P CD iw •H C E G CO 0) 3 0 3 •H rH u U O n3 •H > TS .g 14-1 C a M-l TJ id rH P CD C c P S-i o -H CD D •H jn CO 4-J cr> T3 03 id -H P CD rH CD id E a) £ T3 5-1 G S p T3 03 0 0 C P S-l id CO -K ■K >+-! 130 952 REFERENCES Beardsley, G. F. , Jr., Pak , H. , and Carder, K. L. (1970) Light scattering and suspended particles in the eastern equatorial Pacific Ocean, J. Geophys . Res. , 75, p. 2837-2845. Carder, K. L. , Beardsley, G. F. , Jr., and Pak, H. (1971) Particle size distribution in the eastern equatorial Pacific, J. Geophys. Res . , 76, p. 5070-5077 Charnell, R. L. , Apel, J. R. , Manning, W. Ill, and Qualset, R. H. (1974) Utility of ERTS-1 for coastal ocean observation: the New York Bight example, Mar. Technol. Soc. , 8, p. 42-47. Creager, J. S. , and Sternberg, R. W. (1972) Some specific problems in understanding bottom sediment distribution and dispersal on the continental shelf, in Swift, D. J. P., Duane , D. B. , and Pilkey, O. (editors), Shelf sediment transport: process and pattern, Dowden, Hutchinson and Ross, Inc., Stroudsburg, Pa., p. 347-362. Drake, D. E. (1972) Distribution and transport of suspended matter, Santa Barbara Channel, California, unpublished Ph.D. thesis, Univ. Southern California, Los Angeles, 357 p. Eittreim, S., Ewing, M. , and Thorndike, E. M. (1969) Suspended matter along the continental margin of the North American Basin, Deep-Sea Res . , 16, p. 613-624. Jerlov, N. G. (1968) Optical oceanography. Elsevier Publ. Co. , Amsterdam. Kiefer, D. A., and Austin, R. W. (1974) The effect of varying phytoplankton concentration on submarine light transmission in the Gulf of California, Limnology and Oceanography , 19, p. 55-64. Maul, G. A., Charnell, R. L. , and Qualset, R. H. , Computer enhancement of ERTS-1 Images for Ocean Radiances (in press) , submitted to Journal of Remote sensing of the Environment. 131 953 Pak, H. / Beardsley, G. F. , Jr., Heath, G. R. , and Curl, H. (1970) Light scattering vectors of some marine particles, Limnol. Oceanogr. , 15, p. 683-687. Petzold, T. J. , and Austin, R. W. (1968) An underwater transmissometer for ocean survey work. Scripps Inst. Oceanogr. Ref. 68-69, 5 p. Preisendorfer , R. W. (1958) A general theory of per- turbed light fields, with applications to forward scattering effects in beam transmittance measurements. Scripps Inst. Oceanogr. Ref. 58-37. Zaneveld, J. R. V., Pak, H. , and Plank, W. S. (1973) Optical and hydrographic observations of the Cromwell current between 92°W and Galapagos Islands, J. Geophys Res. , 78, 2708-2714. 132 954 FIGURES Figure 1. Scatter plot of ^go versus suspended solids concentration (mg/1) for surface water of the New York Bight, November 1973. Consult Table 1 for statistical data. Figure 2. Scatter plot of ]_q versus suspended solids concentration (rag/1) for surface water of the New York Bight, November 19 73. Consult Table 1 for statistical data. Figure 3. Scatter plot of j_qq versus suspended solids (mg/1) off southern California. Solid points represent data collected during periods of no coastal runoff; circles repre- sent data during a period of moderate river flow. Figure 4. The volume attenuation coefficient of the sea surface off New York as determined with the Interocean 10 cm pathlength instrument, November 1973. Figure 5. The volume attenuation coefficient at the sea surface off New York as determined with the Visibility Laboratory (SIO) 100 cm pathlength transmissometer, November 1973. Figure 6. Suspended solids in the surface water off New York in November 1973. Values are in mg/1. Figure 7. ERTS-1 satellite image of the New York Bight apex. Imagery data were collected on September 16, 1973; the suspended solids data which are superimposed were collected during September 16-19, 1973. The lower edge of this figure represents 30 miles. Figure 8. ERTS-1 satellite image (September 16, 1973) and beam transmission values, New York Bight apex. Note the light transmission values are in % and were obtained with the Inter- ocean 10 cm pathlength instrument. See text for description of imagery data. 133 955 o u 3 M o to o ro CM* CO 9 _J o CO Q Ui Q Z w co CO o cvj 2 IO L. o ro I in c\i o CNJ m mo d U313W0SSIIAISNVU1 8UJ000I VHdlV 1J4 956 CM V u 3 60 L q ro -L ± ! O in o ro to O ro m cvi q cvi »n o 00 Q U o Ld Q_ CO CO o» in o io cvi cvi —' H313W0SSIWSNVU1 sujooi 135 m o* VHdnv 957 WO OOT VHdlV 13 b 958 cr UJ UJ o co CO oo < CO E o O < Q. < 3 SO 137 959 UJ UJ o CO CO (O < cr E o O O < a. < 01 u D 960 CO 9 _j o w Q yj Q UJ w CO o» a u 3 of) ■H 1j9 961 962 963 Reprinted from: DEEP SEA SEDIMENTS Edited by A. L. Inderbitzen Book available from: Plenum Publishing Corporation 227 West 17th Street, New York, New York 10011 MARINE GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS AND RELATIONSHIPS TO DEPTH OF BURIAL GEORGE H. KELLER Atlantic Oceanographic & Meteorological Laboratories ABSTRACT Marine Geotechnique is a relatively new field which attempts to define and understand the mass physical and chemical properties of sea-floor deposits and the reponse of these materials to applied static and dynamic forces. Although only a relatively small portion of the ocean floor has yet been studied, it appears that it is fea- sible at this stage of our knowledge to define certain interrela- tionships among a number of the physical, electrical, and acoustical properties of these deposits. Most prominent of these correlations are unit weight (density) with water content, porosity with resis- tivity, mean grain size with porosity and density, sound velocity with unit weight and porosity, and reflectivity with porosity and unit weight. In some cases where a relatively large number of anal- yses have been made it has been possible to formulate predicting equations for such properties as unit weight, water content, void ratio, and shear strength. At best, most of the correlations pro- vide only an approximation and are restricted to the sediment type or local area from which the basis for the correlation was developed. INTRODUCTION For a little more than 15 years there has been a concerted ef- fort by a few to investigate the mass physical properties of deep- sea sediments. Much of the initial impetus for these studies was generated by the U. S. Navy's interest in defining the foundational and acoustic characteristics of ocean-floor deposits. The highlights of these early studies have been presented by Richards (1967) and Keller (1968a, 1968b). 77 964 78 KELLER 450r 400 O 350 300 fr? 250 *— z LU >— z 200 o V OL LU ISO t— < £ 100 50 ■GRAIN 1.00 1.10 1.20 1.30 140 1 50 160 170 180 190 2 00 2 10 WET UNIT WEIGHT (g/cm3) Figure 1. Fixed relationship of wet unit weight to water content for two grain specific gravities This field of study, recently referred to as Marine Geotech- nique, has advanced rapidly during these past fifteen years. It has advanced not only in regard to gaining a better understanding of deep-sea sediments, but by sizably increasing the number of re- searchers working in the field. Although there is as yet relative- ly little known about the mass physical properties of deep-sea sedi- ments, a number of interrelationships (Hamilton, 1956; Moore and Shumway, 1959; Richards, 1961, 1962) and regional generalizations made on the distribution of these properties over the North Atlan- tic and North Pacific basins (Keller and Bennett, 1968) and the Mediterranean (Keller and Lambert, 1971) have been defined. With the advent of the M0H0LE Project and later the J0IDES Deep-Sea Drilling Project, a limited amount of mass property data have be- come available from depths as great as 1015 m below the sea floor (Hamilton, 1964; Moore, 1964; Creager et al., 1973). Most of the basic relationships between the index properties of terrestrial deposits were established long ago by those working in soil mechanics. More recent studies of deep-sea sediments have 965 GEOTECHNICAL PROPERTIES : INTERRELATIONSHIPS 79 shown that it may be feasible to develop additional interrelation- ships for submarine deposits, particularly in relating the physical, acoustical, and electrical properties to each other. Owing to the lack of data from many different depositional areas and from a num- ber of sediment types, it is only possible to generalize on these relationships even though the correlation between certain parameters appears to be well established for the data at hand. This discus- sion is an attempt to summarize the most prominent of these inter- relationships as proposed by various researchers as well as to men- tion a few cases where no relationships are found between certain major properties. For the sake of accuracy, where figures have been taken from other sources, they are presented with their original units. I L GRAIN SPECIFIC GRAVITY I I I l l l I I 1 I I 1 1 1 L 450 400 350 •- x o 111 300 5 >- at O 250 200 150 100 50 &5 i— z IXI t— z o < 10 20 30 40 50 60 70 80 90 100 POROSITY (%) Figure 2. Fixed relationship of water content to porosity for two grain specific gravities 966 80 KELLER pel 80 90 100 110 120 130 1.0 12 14 1.6 1.8 2.0 WET UNIT WEIGHT (g/cm^) Figure 3. Fixed relationship of porosity to wet unit weight for three grain specific gravities DISCUSSION Before discussing a number of the correlations that have evolved from recent studies of submarine sediments, it must be pointed out that even with the establishment of what appear to be sound inter- relationships, they can, at best, only be extrapolated to other areas in a very general sense. A graph depicting an interrelation- ship for two parameters from one area may have limited or no appli- cation in another depositional environment. Certain relationships are well established, dating back to the early workers in soil mechanics. For each of the three cases shown, Figs. 1, 2, & 3) curves based on grain specific gravity are estab- 967 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 81 lished for the three interrelationships. Figures 1 and 2 are based upon the author's work and Figure 3 is from Richards (1962). These correlations can be used with any sediment from any environment if the grain specific gravity is known. They provide a rapid method of determining porosity or wet unit weight if water content and grain specific gravity are known (Bennett et al., 1971; Lambert and Bennett, 1972) (Figs. 4 and 5). As shown in each case (Figs. 1, 2, & 3) , considerable change in grain specific gravity is needed be- fore the relationships between the other parameters are appreciably influenced. Despite this relatively small influence of grain spe- cific gravity, care must be used (if specific gravity is not deter- mined) before extrapolating from a series of curves established for one area or deposit to a distinctly different sediment. Atterberg limits have long served as a simple means of classi- fying sediments as to their plasticity, compressibility, and activ- ity (ratio of plasticity index to per cent clay) (Skempton, 1953). Although these limits are commonly determined in the routine analy- sis of submarine sediments, they are usually only used for defining plasticity characteristics. In his study of the Mississippi Delta front, McClelland (1967) found the void ratio and liquidity index of the delta sediments to be functions of the liquid limit and the overburden pressure. Based on these findings, he developed a generalized family of pressure- void ratio curves which allowed the approximation of void ratio knowing the liquid limit, liquidity index, and overburden pressure. Liquidity index was thus shown to serve as an indicator of the state of consolidation. This same study also led him to devising a sec- ond family of curves whereby cohesion could be approximated based, on liquid limit, liquidity index, and water content. Although these families of curves will undoubtedly not be applicable elsewhere, the concept is of interest for possible use with other sea-floor deposits. Water Content As noted above, water content is readily correlated with both unit weight and porosity. Based on 1480 analyses performed on 80 sediment cores collected from the major provinces of the Gulf of Mexico, Bryant and Trabant (1972) have established a curve for the water content-unit weight relationship (Fig. 6) which closely re- sembles Figure 1. Scatter in their data can be attributed to two things: variation of grain specific gravities, or error in deter- mining either water content or wet unit weight. Based on this same study of Gulf sediments a least squares curve was established showing the decrease of water content with depth. This inverse relationship of water content to depth is a 968 81' KELLER i c o o u ID •1-1 cd ■-:, r. > DO CJ CO 2 — c* n3 &o S M ■H C •H . cu c^ a) -a - o cu cfl _! M -a o c g cfl o QJ c c d) PQ «tf A1IAVMO DldlD3dS NIVMO cu u 3 4J 60 c •H cu 969 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 83 common generalization and one that would be anticipated owing to in- creasing overburden pressure with depth. From their study of shear strength and water content, Bryant and Trabant (1972) reported an inverse relationship between these two parameters. A similar relationship has been reported for re- molded sediment by Rutledge (1947) and Bjerrum (1951, 1954). Yet, for natural occurring deposits, this statement can only be made in a very general sense. Water content and sediment grain size are commonly inversely proportional, the coarser the sediment the lower the water content. An exception to this general rule is found in sediments rich in Foraminifera. Although a large number of forams will constitute a sandy texture, the framework of their test with its large central cavity is such that relatively large amounts of water are trapped within the foram thus resulting in a high water content being asso- ciated with this type of coarse-grained material. 20 40 60 80 100 > < 3.20 3.00 2.80 2.60 2.40 WATER CONTENT (%) 50 75 100 200 500 600 O 2.20 2.00 1.80 10 20 40 50 60 POROSITY {%) 100 Figure 5. Nomogram for determining porosity from grain specific gravity and water content 970 84 KELLER 1.4 1.6 1.8 WET UNIT WEIGHT (gm/cc) Figure 6. Relationship of wet unit weight to water content for the Gulf of Mexico (after Bryant and Trabant, 1972) Wet Unit Weight and Porosity The well defined correlation between wet unit weight, porosity, and water content for a given specific gravity was discussed ear- lier. Although not shown, the same inverse relationship of wet unit weight to porosity exists for wet unit weight and void ratio. It is commonly accepted that wet unit weight increases as depth be- low the sea floor increases. This is obviously not a linear func- tion but one dependent on such factors and changes in grain size, cementation, overburden, depositional history, etc. Bryant and TrabanC (1972) have developed a least squares curve, based on their 1480 analyses from the Gulf of Mexico, showing the increase in wet unit weight with depth (Fig. 7). It is clear from this figure that such a curve can serve only as a very rough rule of thumb and con- firms the generalization that density increases as depth of burial increases . Both wet unit weight and porosity are closely correlated with s-ediment grain size. Although the relationships are not linear throughout their respective limits, there is a definite inverse correlation between mean grain size and porosity (Hamilton, 1972) and a directly proportional relationship with wet unit weight. 971 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 85 T3 o c o CO j-> C cO o o o U a) m 8 o a •H X 0) 8 IH o D O 8 E CD h- o X. —' ■u UJ c r-. a) c Vj cfl 3 ,0 o ■ oo cd •H (-J (33/uiB) 1HOI3M UNO 13M 972 86 KELLER Shear Strength Shear strength, as wet unit weight, commonly increases with depth of burial due in part to overburden pressure. In the Gulf of Mexico, Bryant and Trabant (1972) have demonstrated this increase of shear strength down to a depth of 12 m. Studies by both Richards (1962) and Inderbitzen (1969) indi- cate that there is some degree of correlation between shear strength and porosity. Their studies show that if data are taken from a very local area there is often an inverse relationship between these two parameters. It is clearly seen from Figure 8 that there is consid- erable scatter in the data if even two cores are compared and there- fore whatever relationship does exist is rather weak and must be considered with caution. Others have not found even this clear a correlation between the two properties (Moore and Shumway, 1959; Moore, 1964). There appears to be some question as to the relationship be- tween rate of sedimentation and shear strength. Moore (1961, 1964) in comparing sediment from sites in the Gulf of Mexico and the Pa- cific has reported that the rate of shear strength increase is in- versely proportional to the rate of sedimentation (Fig. 9). Inder- bitzen (1969) in his study of the southern California continental borderland found no such correlation. Realizing the limitations of comparing sediments from different areas and environments, the va- lidity of this relationship can only be ascertained from the study of similar sediments affected by different rates of deposition. Although some work has been carried out to determine the ef- fect of organic matter on shear strength, no definitive results are available. More recent studies by Hatcher (1974) offer a slight indication that some correlation exists between carbohydrate content and shear strength (Fig. 10). Hatcher's analysis of ten samples is far short of confirming such an interrelationship but it does offer an interesting problem for further study. Moore and Shumway (1959) , in their study of sediments off Pigeon Point, California, reported a weak positive correlation be- tween sorting and shear strength. Well sorted sediments generally have higher strength than those poorly sorted. In addition to the relationships noted above there are indications that shear strength may well be correlated to some extent with a number of other prop- erties, e.g., percentage sand-silt-clay and plasticity index. In most cases considerably more study is needed before these relation- ships can be taken seriously. At most, studies noted above serve only to point out crude and in some cases questionable correlations. 973 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS l ' "'I 1 — f~ 87 83.3 fis° 80.0 >- t- 1/1 75.0 o Ct o a. 66.7 50.0 i i hi i _J 1 i i n [ ] I I T 1 | 1 1 1 — | — I I II ll I III _l I I ' i " 5.0 - 4.0 - 3.0 2.0 1.0 O < O > 5 10 50 100 200 5 10 50 100 200 SHEAR STRENGTH (dn/cm3xl03) Figure 8. Relationship between shear strength and porosity or void ratio from sediments off southern California (after Inderbitzen, 1969) 2.8 2.6 2.4 2.2 at 2.0 < to 1.8 I 1— 1.6 O Z 1.4 UJ at 12 i/> at 1.0 < 0.8 \s> 0.6 0.4 0.2 0 - i i i i I i i I i ■ 1 East Pacific, Arrhenius (1952) i i i - 2 Mohole, EM8 / - 3-5 Gulf of Mexico, Fisk & McClelland (1959) 2/ - yApp rox. Accum Rafe cm/lOOOyrs 1 0.25 " /3 2 1.0 - // s 4 3 300 // s^ 4 1400 _ ^/^ s' 5 10,000 «, j 1 1 i i i i i . 5 i i i i i 0 10 20 30 40 50 60 70 80 90 100110 120130140 DEPTH BELOW SEA FLOOR (METERS) Figure 9. Variation of shear strength with depth for areas of varying rates of sedimentation (after Moore, 1964) 974 KELLER 200 150 O Z 100 < 50 + +■ /++ + 10 20 CARBOHYDRATE (V. TOTAl DRY WEIGHT) 30 40 Figure 10. Relationship of shear strength to carbohydrate content (after Hatcher, 1973) Resistivity For some time, resistivity has been commonly measured in bore holes. It is readily determined in unconsolidated sediments both in situ and from core samples. Studies by such investigators as Boyce (1967); Kermabon et al. (1969), Chmelik et al. (1969), Sweet (1972), and Bouma et al. (1972) all report much the same interrela- tionships of various parameters to resistivity. The rather defini- tive inverse relationships with water content, porosity, and clay content are clearly shown in Figure 11. A direct correlation with grain median diameter, percent sand (up to 50%), and wet unit weight also has been rather clearly established by these same investigators Acoustics In the past few years the acoustical properties of submarine sediments have received considerable attention. As studies have 975 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 89 _ o 8* c (1) ■■* 4-J »- c rf? Ul o a t- z >^ o CO o r-i <-. (E o 8 u < * (1) •u a o o f~ o M 0J 4-J CO s „ O >! t •u •H 03 £ o (-4 o in < a, -i ^ o o •H 4-1 2 CO U -v •H o > o o o 4-> -H o X t- >> OJ < ±> s or •H ~ Q > 14-4 •H O o 4-J > CO 4-4 •H .H 03 3 (!) O to M OJ 4-1 jn O 4-J a ^ •rl o X. 4-1 o 03 ID C i^4 o o •H 4-1 4-1 U ^ CO CO u> r-H 14-4 81 OJ o o *■" •H V • 4-> K iH CO > h e o - n r>- t- OJ O tf) V-l 4-1 w 3 u 60 ID or •H C fj-i CO s 976 90 KELLER progressed, interest has spread to the interrelationship between the acoustic and physical characteristics of submarine deposits. Rather well defined relationships have been established to the de- gree where it has been shown that mapping of sediment texture, wet unit weight, and porosity by acoustic profiling may be feasible over large areas. Sound velocity. The correlation between sound velocity and sediment porosity has been known for many years; more recently a number of researchers have redefined this relationship for submarine sediments (Hamilton et al., 1956; Nafe & Drake, 1957; Shumway, 1960; Buchan et al., 1972). Although the velocity-porosity relationship is well defined, there is some degree of scatter among the data (Cernock, 1970). A correlation between velocity and wet unit weight is less well defined (Hamilton et al., 1956; Horn et al., 1968), but it does appear that velocity increases as unit weight increases. A somewhat similar relationship with grain size (mean diameter) has also been reported (Horn et al., 1968). A rather poor correlation between velocity and water content has been found by the same in- vestigators from their study of deep-sea cores. The data scatter is considerable and even a crude correlation is questionable. Smith (1971) has shown from his analysis of both shelf and abyssal plain deposits that sound velocity is inversely proportional to such pa- rameters as plasticity index, clay content, and liquid limit. Al- though the scatter is moderate, Smith reports a relatively good cor- relation between these properties. Of curious interest is the fact that very little if any correlation has been found between velocity and calcium carbonate, grain specific gravity, or shear strength. Attenuation coefficient. The energy lost in passing an acous- tic wave through sediment has provided a useful index which can be related to a number of physical properties. This index is the at- tenuation coefficient. Buchan et al. (1972) have clearly shown that as the grain size increases the attenuation increases (Fig. 12). Their study of textural composition also revealed that attenuation increases as the percent sand increases and as the percent clay de- creases. Hamilton's (1972) in situ studies of sediments at water depths ranging from 4 to 1100 m revealed a definite correlation be- tween porosity and attenuation. The relationship is complex, vary- ing for different porosities. As a generalization, Hamilton found that for porosities of 52% or more the attenuation decreases as porosity increases. The reverse relationship was reported for po- rosities ranging from 36 to 50% (Fig. 13) . Reflectivity. The measurement of sound reflected off the sea floor has received considerable attention in the past eight years both in regard to military detection systems and as a means of de- veloping a technique for mapping sediment physical properties from a moving platform. Early studies by Loring (1962) attempted to show that a qualitative acoustic classification of bottom types could be 977 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 91 made based on the intensity of the acoustic bottom reflections re- corded on a Precision Depth Recorder. More recently, Faas (1968) showed the distinct inverse relationship between porosity and the coefficient of reflectivity. Later Smith (1971) showed not only the same results but the equally distinct correlation with wet unit weight (Fig. 14) . The degree of data scatter is so minor that re- flectivity serves as a very good index property for determining either porosity or wet unit weight. Although not nearly as defini- tive as the above relationships, Smith (1971) also has shown there to be an inverse relation between reflectivity and plasticity index. Predictor Equations For those who must have an equation to define a correlation, there are even a few researchers who have gone out on this limb and offered such equations (e.g., Faas, 1968; Hamilton, 1970a, 1970b; Cernock, 1970; and Nacci et al., 1971). After studying eight cores "O Z UJ u O u z © < Z 8.0 © • 7.0 • • • • • 6.0 ■ • 5.0 • • • oo 4.0 • • • • • • • • • 3.0 • • • • • 2.0 - i •• • •• • 1.0 - • t • • •• ». ■ i i i i i i i i i i 6 7 8 9 10 GRAPHIC MEAN (<*>) 11 Figure 12. Relation of sediment mean grain size to the attenuation coefficient (after Buchan et al., 1972) 978 92 KELLER z o i k z Figure 13. Relationship between sound attenuation and porosity (after Hamilton, 1972) Figure 14 . Relationship between reflectivity, porosity and wet unit weight (after Smith, 1971) 0 40 0.35 V * • 0.30 >- C 025 UI —1 u. UI * 0.20 V ' 0.15 V V 0.10 1 1 1 i. 1 1 1 1 1 20 40 60 80 POROSITY (%) 040 0 35 > 0 30 > u 0.25 UJ —I u. UJ " 0.20 0.15 0.10 / .•* i '. J' tS V 100 1.2 1.4 1.6 18 20 WET UNIT WEIGHT (g/cm3) 979 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 93 TABLE 1 PREDICTING EQUATIONS FOR SHEAR STRENGTH, WATER CONTENT AND BULK DENSITY WITH DEPTH FOR SEDIMENTS FROM THE GULF OF MEXICO1 For all data S = 82+(.2)D W = 113. 8-(.045)D BD = 1 .44+( .00015)D n = 1480 Area I S = 133+(.14)D W = 97.0-(.037)D BD = 1. 52+( .00011)D n = 264 Area II S = 65+(.2)D W = 120. 3-( .055)D BD = 1.41+( .00018)D n = 516 Area III S = 41+(.26)D W = 121. 4-( .050) D BD = 1.40+( .00018)D n - 343 Area IV S = 99+(.5)D W = 128. l-(0. 29) D BD = 1. 38+( .00008)D n = 87 Area V S = 156+(.18)D W = 104. 4-( ,009)D BD = 1 .45+( .00002)D n = 112 Area VI S = 148+(.21)D W = 102. 7-(.026)D BD = 1. 48+( .0001)D n = 151 S = Shear strength in PSF D = Depth below mudline in cm W = Water content (% dry weight) BD = Bulk density (gm/cc) n = Number of analyses From Bryant and Trabant, 1972 from St. Andrew Bay, Florida, Holmes and Goodell (1964) attempted to determine the interrelationship of a number of the sediment phys- ical properties. Based on their statistical analyses of these data, they derived the following equation for determining shear strength: [Shear strength (g/cm2) = -1.089 water content (%) + 0.254 depth in core (cm) + 0.021 Kaolinite/Illite] 980 94 KELLER Based on the study of 80 sediment cores from various sectors of the Gulf of Mexico, Bryant and Trabant (1972) formulated predicting equations for shear strength, water content, and wet unit weight versus depth below the bottom for each of six provinces of the Gulf (Table 1) . On yet a broader scale, A. F. Richards (personal communication, 1972) has statistically analyzed a large collection of physical properties data (18,000 analyses) from both the Atlantic and Pacific basins. This has lead to a series of equations for the determina- tion of wet unit weight (y sat) , void ratio (e) , and water content (W) (Table 2) . SUMMARY This discussion has attempted to present the state of our knowledge concerning the interrelationships of various mass physi- cal, electrical, and acoustical properties of submarine sediments. Obviously studies to date have not been able to examine all the various environments or sediment types found on the sea floor. Caution, therefore, is warranted in the acceptance of a number of the correlations presented here. The general pattern or relation- ship found in the various correlations will probably continue to be valid as more data become available, but shifting of curves can be expected . Care must be exercised in attempting to apply a number of the curves presented here to areas other than those from which they TABLE 2 PREDICTING EQUATIONS FOR WATER CONTENT, WET UNIT WEIGHT AND VOID RATIO FOR NORTH ATLANTIC AND PACIFIC SEDIMENTS2 y , = 2.4329 - 2.0661 x 10 2W + 1.6645 x 10 V - 6.7536 x 10 ?W3 + sat 1.0663 x 10 9W4 e = 0.01045 + 0.02725W W = 4.0354 + 35.1216e W = 2966.94 - 4481.679y + 2317. 880\2 - 405.513^ sat sat sat 2 From A. F. Richards, personal communication 981 GEOTECHNICAL PROPERTIES: INTERRELATIONSHIPS 95 u H fa H O < fa O •H CJ ^ o> 4-1 ft •H C/3 > rd n U •H o nj j-i >, to C CO ■H CO o s^? u o fa 00 in co CO CO CM CO CM CM CM n CM CM 00 00 m M c ^ OJ ~x! h cd £j ■u Ph u en M bO in ^^ Cd 0) JS CO 4_) C 01 u 4-J c & o u }H T3 0) 4J S^S cd s ■u Xi OJD •H 0) S ^~N CO CO ■U 6 s •H --\ u s CO ■*** t3 A! 60 CO CF1 CO r-« in co • CM ON o o> o CM ^ m ^0 00 /-N H ^^ • in <3"\ T— I 00 o> CM O /-N o ^ o ^ O -~ s O /-N in m o o CM CM CO CO CO CO uo in v£> vO CM CM m m o o rH ,-H o- -d- M .H e e OJ 6 e M cd •H > J s ■5j U 2 s «S < Ph 982 96 KELLER o o CM O a r~- w o> H ^H < CJ •» c • J CO OO u 4-1 4-J D< 0) C o a) u 4-> 4-1 H U < 0) n 4-J i x: o oo i—i ■H 0)<"O s 6 4-1 cj: a) .■^ 3: ii 4-1 CO •H 6 e o 3 ^\ 0£ J3 S-i oo o a B CO a) o u c o M •H o m N CM LO vjO ^D r-~ n vo vT> I— I m u~l O \D oo m co r-- mtj ^d ^o O r^ vo >x> m m r~- cti k ^o in O^ i— t cm I I I O O r- r^ H M I I I O O r- m m DO H (M I I I O 00 c- >. u a) a co v u o CJ D \C M3 O I"*" -tf r~» ^o ^d r^ co o co <}• CO \D CM H CM a*, MD M3 o md O H O M in rv 0C oo o> r~- r-» 1 — "j CM CM 4J ■H > r-^ oo O •H r-~ r-» CC JJ r j CM CM CO C CO 00 00 O 00 r--. r*. r-~ r i Csl CM u M O CJ < m cj a o N •H M O a o m O 14J o\ CJ> -a- cm cm co in , where c is cohe- sion, a the effective stress, and the angle of internal friction. When cohesive, saturated sedi- ments such as those examined in this study are stressed without loss of pore water, they re- spond to the applied load as if they were ma- terials with an angle of internal friction of zero (4> = 0). Shear strength is thus equal to cohesion (rf = c), and the two terms become synonymous for the purpose of this discussion. A more detailed discussion of this subject can be found in such soil-mechanics texts as those by Scott (1963) and Terzaghi and Peck (1967). Measurement of shear strength was made by means of a laboratory vane apparatus (Evans and Sherratt, 1948). Basically, the test con- sists of inserting a small four-bladed vane (1.3 cm in diameter and 1.9 cm long) into the sediment and applying an increasing torque (vane rotation, 6°/minute) until shear occurs (Richards, 1961). Although no shear-strength measurements were obtained from sedimentary units 1 and 2 in core A, the buff calcareous layers (cocco- lith mud) appeared to have a much greater strength than the underlying organic-rich ma- terial of "unit 2. The calcareous layers had a custardlike* texture and resilience. Part of this strength may have resulted from the loss of moisture from this part of the core, but this is not considered to be a major factor. Shear- strength measurements in organic-rich unit 2 proved futile, because the material could not be sampled adequately for use in the vane shear test. This material literally flowed as a slurry when not confined in a container. As shown in Figure 2, shear-strength values are extremely low, even below a depth of 60 cm. 990 334 George H. Keller CORE A SANO.SllT.Cl.AY SHIAI STIENCTH UNIT WIIOHT (%) (9/««Jl (•/«<) I 50 100 0 50 100 1.50 WATSI CONTENT SPECIFIC OIAVITY rOIOUTY C.COj |% D(Y WT.| (X) (X) 200 400 too 1(0 1 JO 2 40 0 50 100 0 50 100 Z E 0 1 .0- v — 20- \ 30- :; 2 *o- ' so 60- m 70 > J • 0 / 90 \ ioo- i 3 no- V 120- \ 130- ► j£:v!*:::-:":¥; 140 i 150 / 160- *■ \ ...""■:■■ \ .70- r* \ • j 190 \ 1»0- !.. : J Fig. 2 — Depth profiles of selected mass physical and chemical properties. Three pronounced sedimentary units are identified by numbers 1, 2, and 3 at left margin. Some of these values (e.g., 10-14 g/cm2) are the lowest yet recorded for marine sediments at a comparable depth below the seafloor. CORE B ANO.Slll.ClAY SMCIFIC GDAVITY CoCO (%> IT.) 50 100 110 2 20 2 60 0 50 Fig. 3 — Depth profiles of selected mass physical and chemical properties. Three pronounced sedimentary units are identified by numbers 1, 2, and 3 at left margin. Sensitivity, the ratio of natural to remolded shear strength, provides a measure of the strength loss due to disturbance. Within the tested interval of core A, sensitivities were found to range from 3 to 6.2, indicating a loss of strength on the order of 60-80 percent in the disturbed or remolded state. Such sediments are classed as medium to very sensitive, based on a classification system commonly used in engineering practice (Rosenquist, 1953). Unit Weight Mass unit weight, or wet bulk density as commonly used incorrectly by some, is the weight per unit of total volume of a sediment mass, regardless of the degree of saturation (ASTM, 1967). Sediment densities in core A are considerably lower than those commonly found in deep-sea deposits. The unique charac- teristics of sedimentary unit 2, which has a high organic content, are clearly shown by the low unit weight of 1.07 g/cm3. This unit weight is the lowest the writer has found in his examina- tion of submarine sediments. Although not com- mon in marine sediment, such low densities are common in peat deposits. Throughout the sampled interval, unit weight increases steadily with depth, as is common in sedimentary de- posits. 991 Physical Properties of Some Western Black Sea Sediments 335 Water Content Water content (IV), as used in engineering (geotechnical) practice, is expressed as a per- cent of the ratio: weight of water to weight of oven-dried solids. Geologists, however, com- monly use water content expressed as a per- centage of the total wet weight of the sediment sample ( Wc). In this discussion the engineering usage is followed. Conversion of these values to percent of the total wet weight of, the sediment can be made from the relation Wc W 1 +W xioo. Water content throughout core A was ex- tremely high. The organically rich unit extend- ing from 18 to 62 cm has an unusually high water content (maximum 700 percent). Un- doubtedly, this high water content is a result of the fiberlike characteristics of the organic matter, which is composed largely of tubular and lamellar membranes as well as organic fragments resemb'ing bacterial cell walls (Degens et al., 1970). This water content is the highest value yet reported in a submarine sedi- ment. In the organic-rich unit, water content decreases abruptly with depth. The abrupt de- crease in water content continues to the upper contact of the next sedimentary unit, below which the rate of decrease is much less. The abrupt reduction in water content in unit 2 undoubtedly reflects the influence of loading and a relatively high rate of expulsion of water from this material. Grain Specific Gravity The three sedimentary units of the Black Sea basin that were studied arc delineated clearly by the specific-gravity properties of their grains. The uppermost unit, composed of microlam- inated layers of high carbonate content inter- layered with organic material, is characterized by intermediate specific gravities (2.19-2.47)." However, in the underlying unit, which has a high organic content, grain specific - gravities (1.89-2.33) are well below those for sub- marine sediments. These low values are only slightly above values commonly found in peat deposits. Within the lowermost unit, specific gravities range from 2.57 to 2.74, and are sim- ilar to those reported for submarine deposits composed primarily of terrigenous material (Keller and Bennett, 1970). Although the spe- cific-gravity profiles of cores A and B (Figs. 2, 3) are of similar character, the values are slightly higher in core B. A comparison of grain specific gravities from the organically rich units of these two cores reveals much higher values and a much less pronounced de- cline in specific gravity within the unit in core B. These observed differences possibly are at- tributable to the greater influence of drainage from the Danube and Dnepr Rivers on the Dan- ube fan deposits than on deposits of the abyssal plain. Porosity Porosity is the ratio of the volume of voids (pores) in a given sediment mass to the total volume of the mass (ASTM, 1967). On the basis of the measured water content, unit weight, and specific-gravity values of grains, the void ratio e (the ratio of the volume of voids to the volume of solids) can be calculated. Porosity, n, is then determined by use of the equation X100. 1 +e Porosity, as in the case of water content, is relatively high throughout the length of core A; values range from 71 to 95 percent. As might be expected, the highest values (90-95 percent) occur in the organically rich sedimentary unit and decrease gradually below that depth. To the writer's knowledge, no value as high as 95 percent has been reported for any deep-sea deposit. Calcium Carbonate Sedimentary unit 1 has numerous laminae of high carbonate content with intervening sapro- pelic layers. In their detailed study of a sedi- ment core from the eastern sector of the Black Sea, Ross et al. (1970) reported calcium car- bonate contents of 24-64 percent for this upper unit. Cores A and B have correspondingly high carbonate contents in the same interval, but differ considerably in regard to other proper- ties. Samples from 5-cm intervals, which in- cluded several layers, showed carbonate content of core A to be higher (46-81 percent) than that of core B (44-60 percent). Within the underlying organic-rich sedimentary unit, a sig- nificant reduction in calcium carbonate content was found^ in both cores; these results are in agreement with the findings of Ross et al. (1970). On the basis of the entire cored in- terval, sediments from the area of the Danube fan (core B) appear to have a lower carbonate content than the abyssal-plain deposits. 992 336 George H. Keller 1*0 150 140 . • CORE A 130 „ □ CORE B 120 no S 100 ? 90 >• H bo u 1 (3) ^/ P 70 «/» < 60 a. 50 40 m/ ORGANIC CLAYS 13) / • AND 30 D^ 13) INORGANIC SILTS OF 20 (3) HIGH COMPRESSIBILITY 10 0 i i/ I 1 I I 1 1 1 1 1 1 I I 1 I I 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 1(0 190 200 LIQUID LIMIT Fig. 4 — Plasticity chart; values in parentheses indicate sedimentary unit (see Figs. 2, 3) from which samples were taken. Plasticity By. use of Cisagrande's (1948) relatively simple classification system based on the plas- ticity characteristics of a sediment, the three sedimentary units are found to possess only slightly different properties (Fig. 4). Although samples taken from all three sedimentary units have a high degree of plasticity, there is a general decrease in plasticity from the upper to the lower unit. It is not surprising to find units 1 and 2 classified as organic clays, whereas unit 3 samples are classified as both organic and inorganic clays, depend- ing on the layer sampled. Summary Mass physical properties of deposits from the western Black Sea appear to have very little in common with those found in other seas at comparable oceanic depths. The geo- logic history of the basin appears to have been largely responsible for the unique chem- ical and circulation characteristics of the Black Sea, and these characteristics, in turn, have contributed to the unusual properties of the Black Sea sediments. These sediments, like the overlying water, are well stratified. Correlation of three distinct sedimentary units throughout much of the basin is in itself un- usual considering the areal extent of the Black Sea. It is apparent that the three units rep- resent very different depositional conditions (Ross et al., 1970). This difference is clearly evident from visual examination of the cored material, and is emphasized further by the mass physical and chemical properties of these sediments. The uppermost sedimentary unit (unit 1), approximately 20-30 cm thick, consists of al- ternate microlaminated layers of coccolith and sapropelic mud, apparently representing a cyclic sedimentation pattern. The unit is characterized by a high carbonate content (44-81 percent) and grain specific-gravity values in the intermediate range (2.19-2.47). Near the Danube fan the occurrence of coarser sediments results in slightly higher specific-gravity values of grains and lower car- bonate contents than those found in the abys- sal-plain ^deposits of the western Black Sea. Although no unit-weight or shear-strength measurements were made in the upper sedi- mentary unit, the material appears to have a higher unit weight and shear strength than the unit directly below. Unit .2, about 40 cm thick, is distinguished 993 Physical Properties of Some Western Black Sea Sediments 337 by its very high content of organic matter. This unit is essentially devoid of sand-sized material in the abyssal-plain deposits, but it contains approximately 25 percent sand in those sediments from the upper part of the Danube fan. The unusual composition and fibrous texture of this deposit result in unique mass properties. Unit-weight values and spe- cific-gravity values of grains from the or- ganic-rich sequence of the abyssal plain are the lowest that have been observed in sub- marine sediments. These values are similar to those commonly found associated with peat deposits. This similarity is not surprising in view of the composition of the organic ma- terial— i.e., a high concentration of lamellar and tubular membranes (Degens et ai, 1970). Water contents and porosities are exceptional- ly high for a submarine deposit, but the values would not be unusual for sediments largely composed of peat. A relatively high permeability appears to characterize this unit, as indicated by the abrupt decrease of water content with depth. Sapropelic muds from the Mediterranean basin have similar mass physical properties (Keller and Lambert, 1972), although they are not as extreme as those observed in unit 2. Shear strength or cohesion of this material is estimated to be extremely low, possibly on the order of 1-3 g/cml Unit 3 is characterized by light- and dark- gray silty clay of higher grain specific grav- ity than that of the overlying sediments. Shear strength and unit weight are well be- low values generally reported for submarine deposits. Water contents and porosities are lower than in the overlying units, yet higher than most recorded for submarine sediments. Although there is an obvious distinction among the three sedimentary units of the up- per part of the Black Sea basin deposits, their plasticity characteristics are not drasti- cally different. Many of the mass physical properties of these Black Sea samples closely resemble the characteristics of some lake or high-peat-con- tent deposits rather than those of deep-sea sediments. References Cited ASTM (American Society for Testing Materials), 1967, Book of ASTM standards including tentatives, part 2: Philadelphia, Am. Soc. for Testing Materials, p. 532-537. Bukry, D., et ai, 1970, Geological significance of coccoliths in fine-grained carbonate bands of post- glacial Black Sea sediments: Nature, v. 226, no. 5241, p. 156-158. Casagrande, A., 1948, Classification and identification of soils: Am. Soc. Civil Engineers Trans., v. 113, p. 901-931. Degens, E. T, S. W. Watson, and C. C. Remsen, 1970, Fossil membranes and cell wall fragments from a 7000-year-old Black Sea sediment: Science, v. 168, no. 3936, p. 1207-1208. Evans, I., and G. G. Sherratt, 1948. A simple and convenient instrument for measuring the shear re- sistance of clay soils: Jour. Sci. Instruments and Physics in Industry, v. 25, p. 411-414. Keller, G. H., and R. H. Bennett. 1970, Variations in the mass physical properties of selected submarine sediments: Marine Geology, v. 9, no. 3, p. 215-223. and D. Lambert, 1972, Geotechnical properties of submarine sediments, Mediterranean Sea, in D. J. Stanley, ed.. The Mediterranean Sea, a natural sedi- mentation laboratory: 8th Internat. Sedimentological Cong. Proc; Stroudsburg, Pennsylvania, Dowden, Hutchison and Ross, p. 401-415. Richards, A. F., 1961, Investigations of deep-sea sedi- ment cores. I. Shear strength, bearing capacity, and consolidation: U.S. Navy Hydrographic Ollice Tech. Rept. 63, 70 p. and G. H. Keller, 1961, A plastic-barrel sedi- ment corer: Deep-Sea Research, v. 8, p. 306-312. Rosenquist, I. Th., 1953, Considerations on the sensi- tivity of Norwegian quick-clays: Geotechnique, v. 3, p. 195-200. Ross, D. A., and E. T. Degens, 1974, Recent sediments of Black Sea, in E. T. Degens and D. A. Ross, eds., The Black Sea — geology, chemistry, and biology: this volume. and J. Macllvaine, 1970, Black Sea: recent sedimentary history: Science, v. 170, no. 3954, p. 163-165. Scott, R. F., 1963, Principles of soil mechanics: Palo Alto, California, Addison-Wesley Pub. Co., 550 p. Terzaghi, K., and R. Peck, 1967, Soil mechanics in engineering practice, 2d ed.: New York, John Wiley & Sons, 729 p. Zenkovich, V. P., 1958, Morfologiya i dinamika so- vetskikh beregov Chernogo morya (Morphology and dynamics of Soviet Black Sea): Moscow, Izd. Akad. Nauk SSSR, v. 1, p. 126-146. 994 VOL 79. NO 8 JOURNAL OF GEOPHYSICAL RESEARCH MARCH 10, 1974 Magnetic Anomaly Sequence in the Central North Atlantic Robert K. Lattimore,1 Peter A. Rona, and Omar E. DeWald NO A A Atlantic Oceanographic and Meteorological Laboratories. Miami. Florida 33149 Marine geophysical investigations in 1970 and 1971 have established the sequence of sea-floor- spreading magnetic anomalies within the corridor extending from Cape Hatteras in North America to Cap Blanc in Africa The standard 'Tertiary' anomalies out to 25 or 26 (64-66 m.y B.P.) as well as the J and K anomalies can be recognized and correlated among the four traverses. Displacements of the anomalies suggest a complex fault pattern that may be associated with the Kane fracture zone. A spreading chronology for the past 60-65 my. has been derived by modeling: the overall relative spreading rate is of the order of 1-1.2 cm/yr, the slower intervals ranging from 10 to 15 m.y. B.P. and be- ing centered about 30 my B.P.: a possible increase in spreading rate is marked at about 60 my. B.P. The imperfect symmetry of the magnetic anomaly profiles about the mid-Atlantic ridge as well as the low amplitude and the poor definition of the individual anomalies are, according to hypotheses of Matthews and Bath (1967) and Vine and Morgan (1967), consistent with formation of the ridge by dike injection over a relatively wide zone. Magnetometer data collected by the NOAA ship Dis- coverer as part of the 1970 and 1971 trans-Atlantic geotra- verse (TAG) program of the National Oceanic and At- mospheric Administration advance our knowledge of the structure and geologic history of the corridor extending from Cape Hatteras in North Carolina to Cap Blanc in Spanish Sahara-Mauritania [Lattimore el al., 1972]. Magnetic total- field measurements made along four traverses (Figure 1) were reduced by using international geomagnetic reference field 1965 coefficients [IAGA Commission 2. 1969]; the residual anomaly profiles are illustrated in Figure 2. Key anomalies, identified after Heirtzler et al. [1968], Rona el al. [1970], Vogt et al. [1971], and yogi and Johnson [1971], are indicated on the profiles and located on the track line map. Identification of the anomalies is based on a sea-floor- spreading model constructed by using the magnetic chronology of Heirtzler et al. [1968], modified for the interval 0-4.5 m.y. B.P. after the chronology proposed by Cox [1971]. The corresponding magnetic anomalies were computed by us- ing the technique developed by Talwani and Heirtzler [Heirtzler et al.. 1962]. Because of the poor lateral symmetry and the variability from profile to profile, specific anomalies could not always be identified directly; correlation of profiles often required matching of peaks and troughs along segments several hundreds of kilometers in length. For reasons that w ill be explained in the next paragraph, anomaly 3 1 was identified only on the basis of shape and amplitude without considera- tion of position in a synthetic profile. West of the mid- Atlantic ridge our identifications (except that of anomaly 5) and the overall magnetic pattern are in close agreement with those deduced by Pitman et al. [1971 ] and Pitman and Talwani [1972]. Our identifications of anomalies 5. 2!, and 25 east of the ridge are slightly different from those of these workers, but the effect of these differences on the inferred pattern of faulting is negligible. As Figure 3 shows, a magnetic anomaly pattern can be produced from the modified Heirtzler et al. [1968] chronology, which closely matches an observed profile for anomalies out to 25 or 26 (64-66 m.y. B.P.). Beyond anomalies 25 or 26, order-of-magmtude changes in spreading 1 Now at E. D'Appolonia Consulting Engineers, Inc., Pittsburgh, Pennsylvania 15235. Copyright © 1974 by the American Geophysical Union. rate between successive anomalies must be postulated to ob- tain agreement with the observed profiles. One possible ex- planation for the absence or the very poor development of these anomalies is the change in direction of motion of North America with respect to Europe. The spreading pattern [Pit- man and Talwani. 1972], however, precludes a change of sufficient magnitude to account for this variation in purely geometrical terms. The spreading history implied by the model for traverse 71/2 is shown in Figure 4. The two halves of the model were determined independently, so that the apparent reductions in spreading rate between 10 and 15 m.y. B.P. and centered about 30 m.y. B.P. probably represent real episodes. The magnetic profiles (Figure 2) do not exhibit the near- perfect bilateral symmetry about a median magnetic anomaly that is generally expected of patterns associated with mid- ocean ridges. As is shown by profile 71 /2 (Figure 3), the center of symmetry for anomalies 1-25 varies by as much as 25 km. (The profiles illustrated in Figures 2 and 3 are not corrected for variations in ship's heading. Within that portion of the traverse including anomalies 1-25, ship's heading ranges from I00°T to I08°T; at most this variation would account for about half the asymmetry observed in the profile.) Specific anomalies also vary considerably in shape and amplitude between adjacent profiles, and two of the four traverses lack a well-defined median anomaly. In the two profiles that lack a large median anomaly (70 and 71/3) the median valley is partly occupied by a topographic feature standing Vi km or more above the surrounding terrain. Changes in the linear trends of the correlated anomalies may be attributed to offsets along faults, possibly associated with the Kane fracture zone (Figure I). Matthews and Bath [1967] and Vine and Morgan [1967] used model studies to demonstrate that the large magnetic anomaly associated with the center of the ridge can result from random dike injection in which the injection pattern follows a Gaussian normal distribution about the axis of spreading. Their studies suggest that amplitude and definition of the individual anomalies as well as symmetry in the magnetic profile vary inversely as the width of the zone of in- jection. This relation of the perfection of the anomaly pattern to the width of the zone of injection provides an explanation for the poor symmetry and imperfect development of in- 995 1208 Lattimore et al: Anomaly Sequence CANAIT ISLANDS., /FRACTURE 20NE •**• ^ NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION SHIP DISCOVERER TRANS-ATLANTIC GEO-TRAVERSE 1970-1971 /,':/ AFRICA Fig. 1. Index map showing track lines, locations of key magnetic anomalies, and postulated sea floor structure associated with the Kane fracture zone. Outside the track lines the location of the anomalies is taken from Pitman and Talwam [1972]. The fault patterns were inferred only from the magnetic anomalies. Arrows indicate sense of displacement along faults; time of displacement is indeterminate The pattern west of the mid-Atlantic ridge axis is consistent in trend with topographic features mapped by Johnson and Vogt [1971]; the existence of small fracture zones trending roughly nor- mal to the ridge axis was established at 3I°W by Harbison and Rona [1972] and Rona el al. [1974]. dividual anomalies in the Cape Hatteras-Cap Blanc corridor, namely, that intrusive activity has taken place over a zone several tens of kilometers wide. The width of the median valley in our profiles is rarely more than 20 km. However, as Deffeyes [1970] points out, dike injection and extrusion can- not be limited to the median valley, and it is not necessary that there be a direct correspondence between the width of the median valley and the width of the zone of intrusion. A relationship may exist between the postulated wide zone of in- jection and the intense fracturing of the sea floor, which has been shown in the western part of the corridor [Johnson and yog:. 1971], Although the dike injection mechanism also offers an explanation for the absence of a median anomaly from two of the profiles, the reason more likely lies in the presence of large volumes of rock forming the topographic prominences cited. In summary, magnetometer data from TAG confirm the presence, immediately north of the Kane fracture zone, of the standard sequence of sea-floor-spreading anomalies with the possible exception of Tertiary anomalies 26-32. From lateral displacements of these anomalies a pattern of faulting can be inferred that is consistent with bathymetric data from the Ber- muda rise presented by Johnson and Vogt [1971 ] and from the eastern North Atlantic by Harbison and Rona [1972] and Rona et al. [1974]. Relative spreading rates averaging about 1.2 cm/yr, recognized throughout the North Atlantic [Pitman and Talwani. 1972], are applicable here, although the derived chronology suggests intervals of reduced spreading between 1000 « -l 0- O-r-r SIS 13 21 IS K-2 K-6 K-12 J-6 J-20 0 400 kn ipti J-20 J-6 K-12 K-6 K-2 3V 2S 21 13 -~^VW jf\ ^JVrVl/l{AL,;4vv^ Jjw^^AiW^W p^ A-W^W^^^^^ ^^^^Y^NAWfiA^ ^Ir^^rv/W^^wryA-vV f1M ^*\A^*vMAr^^|,!VV. Fig 3. Profile 71 '2 (top) and the corresponding synthetic profile computed bv using the method in Heirtzler et al. [1962]. The magnetic chronology of Heirizler ei al. [1968] was used with modifications of the 0- to 4.5-m.y,-B.P. interval as was suggested by Cox [1971]; the center of spreading bears 033. 2°T. and the profile is oriented I05°T. Other parameters of the model are as follows: J = 2400. 1 200. and 800 X 10"! emu for the median anomaly, anomalies 1-5. and anomalies beyond 5. respectively: D = 341°. / = 49.6°: thickness of magnetic source layer is 0 4 km: depth to magnetic source layer is 0.4 km; depth to magnetic source layer is variable (average values are obtained from the bathymetric profile) Profile 71 '2 also shows that the center of symmetry varies slightly for different anomalies, e.g.. 1 . 5, and 1 3. The spreading rates are based on the chronology of Pitman et al. [19711. 10 and 15 my. B.P. and centered about 30 my. B.P. Minor asymmetries in the anomaly pattern and degradation of the amplitude, and definition of the individual anomalies are con- sistent with formation of the mid-Ailantic ridge by dike injec- tion over a relatively wide zone in a manner proposed by Matthews and Bath [1967] and Vine and Morgan [1967]. O 4i Z 5 r-e < , a, 3- acoc £>- */>\ •^*->j r J -u2- < . i. ~h r — T , f~W z£i- UJ *1 ! LLlr-' 1-1 at < £ o < 0 10 20 30 40 50 60 70 MY B.P. Fig. 4. Apparent half rates of sea floor spreading determined for profile 71/2. based on the chronology of Pitman et al [1971]: W and E indicate west and east of the mid-Atlantic ridge axis. Acknowledgments Study of the magnetic data collected during the 1970 and 1971 TAG investigations was supported by funds from the National Science Foundation International Decade of Ocean Ex- ploration. R S Dietz gave helpful advice. The manuscript was reviewed by L M. Dorman and George Peter. H. W Keith. Jr.. R. C. Munson. and the officers and crew of the NOAA Discoverer provided excellent cooperation. References Cox. A., Chronology of earth's magnetic field reversals. Ceotimes. 16. 23. 1971. Deffeyes, K. S.. The axial valley: A steady-state feature of the terrain, in The Megaiectonics of Continents and Oceans, edited by H. John- son and B. L. Smith, pp. 194-222, Rutgers University Press. Brunswick. N. J., 1970. Harbison, R. N . and P. A. Rona, Abyssal hills in the eastern central North Atlantic (abstract), Eos Trans. AGV. 53. 408. 1972 Heirizler. J. R., G. Peter. M. Talwani, and E. G. Zurflueh. Magnetic anomalies caused by two-dimensional structure: Their computation by digital computer and their interpretation. Tech Rep 6. pp. 1-42. Lamont-Dohertv Geological Observatory, 1962. Heirizler. J. R . G. O Dickson. E M. Herron. W. C. Pitman III. and X. LePichon. Marine magnetic anomalies, geomagnetic field rever- sals, and motions of the ocean floor and continents, J. Ceophvs. Res . 73. 2119-2136. 1968. IAGA Commission 2. Working Group 4, International geomagnetic reference field 1965.0. J Geophys Res.. 74. 4407-4408. 1969. Johnson, G. L., and P. R. Vogt, Morphology of the Bermuda rise, Deep Sea Res.. 18. 605-617. 1971. Larson. R. L . and W. C. Pitman III. Worldwide correlation of Mesozoic magnetic anomalies, and its implications. Geo!. Soc. Amer. Bull . 83. 3645-3662, 1972. Lattimore. R. K.. P. A. Rona, and O. E. DeWald. Magnetic anomaly sequence, central North Atlantic Ocean (abstract). Eos Trans. ACL7. 53. 407. 1972. Matthews. D. H.. and J. Bath, Formation of magnetic anomaly pattern of mid-Atlantic ridge. Geophvs. J. Roy. Astron. Soc. 13. 349-357. 1967. Pitman. W. C . III. and M. Talwani, Sea-floor spreading in the North Atlantic, Geol. Soc. Amer. Bull.. 83. 619-646. 1972. Pitman. W. C. III. M. Talwani, and J. R Heirtzler, Age of the North Atlantic Ocean from magnetic anomalies. Earth Planet Sci. Lett.. II. 195-200. 1971. Rona, P. A.. J. Brakl, and J. R. Heirtzler. Magnetic anomalies in the northeast Atlantic between the Canary and the Cape Verde islands, J Geophys. Res.. 75. 7412-7420. 1970. Rona, P. A.. R. N. Harbison, and S. A. Bush, Abyssal hills in the eastern central North Atlantic, Mar Geol.. in press, 1974. Vine, F. J., and W. J. Morgan, Simulation of mid-ocean ridge anomalies using a random injection model, paper presented at 1967 Annual Meetings. Geol. Soc. of Amer.. New Orleans. La.. Nov. 20-22. 1967. Vogt, P. R., and G L. Johnson, Cretaceous sea-floor spreading in the western North Atlantic, Mature. 234. 22-25. 1971. Vogt. P. R., C. N. Anderson, and D. R. Bracey. Mesozoic magnetic anomalies, sea-floor spreading, and geomagnetic reversals in the southwestern North Atlantic, J. Geophys. Res.. 76. 4796-4823, 1971. (Received April 2. 1973: revised November 28, 1973.) 997 Marine Geology, 17(1974): 79—102 ©Elsevier Scientific Publishing Company, Amsterdam — Printed in The Netherlands LARGE-SCALE CURRENT LINEATIONS ON THE CENTRAL NEW JERSEY SHELF: INVESTIGATIONS BY SIDE-SCAN SONAR THOMAS F. McKINNEY' *, WILLIAM L. STUBBLEFIELD2 and DONALD J. P. SWIFT2 ' Department of Geology, Vassar College, Poughkeepsie, N.Y. (U.S.A.) 2 National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratories, Miami, Fla. (U.S.A.) (Accepted for publication April 9, 1974) ABSTRACT McKinney, T. F., Stubblefield, W. L. and Swift, D. J. P., 1974. Large-scale current lineations on the central New Jersey shelf: investigations by side-scan sonar. Mar. GeoL, 17: 79-102. Two morphological orders of ridge and trough topography can be recognized on a terraced segment (at 37 m) of the central New Jersey shelf: (1) a first-order system with ridges to 14 m high, 2—6 km apart, in a Z-shaped pattern trending to the NNE, and (2) a second-order system with ridges 2—5 m high, 0.5—1.5 km apart and trends to the NE. Side-scan mapping together with submersible observations and bottom samples indicate a third-order system of large-scale current lineations which has been imprinted across the first- and second -order systems. The lineations are low relief forms (to 1.5 m high) which occur as elongate zones of textural contrast arranged in furrows, bands, patches and ribbons and display a uniform directional trend to the ENE. The morphology of the lineations appear to vary in response to the nature of the bottom. The lineations are narrow (10 — 25 m apart) and have no detectable relief in troughs and wider (to 75 m apart) and higher (to 1.5 m high) on ridges, especially second-order ridges of fine sand. Also revealed are wave ripple patterns and a pattern related to the outcropping of Pleistocene/Holocene units in trough bottoms and lower flanks. It is suggested that the first- and second-order systems developed during earlier stages of the Holocene transgression in response to a hydraulic regime of the inner shelf. The first-order system may have inherited some of its morphology from an older system, but did respond to a Holocene tidal regime adjacent to a major estuary. The second-order system developed in slightly deeper water, subsequent to the resumption of the transgression after the 37-m stillstand. The third-order lineations appear to be a response to the helical-flow structure within the flow field of a major shelf storm. Ridges of the central shelf may be maintained by alternate periods of oblique sweeping during storms, resulting in a net transport of fine sand out of the troughs and up on the ridges. Subsequent wave reworking returns the fine sand to the troughs. *Present address: Dames and Moore, Consultants in Environmental and Earth Sciences, 6 Commerce Drive, Cranford, N.J. 07016, U.S.A. 998 80 INTRODUCTION Considerable effort has been concentrated in recent years in determining the origin of the ridge and swale topography on the inner continental shelf of Eastern United States. Duane et al. (1972) review the problem and conclude that the shoreface-connected shoals appear to be forming in response to the interaction of south-trending, shore-parallel, wind set-up currents with wave- generated bottom currents during winter storms, while the isolated shoals on the inner shelf have been abandoned as the shore retreated in response to sea-level rise. This concept was proposed in part by Moody (1964) for Bethany Beach, Delaware, and was supplemented by reconnaissance studies in the False Cap, Virginia, area (Swift et al., 1972a). The latter work included some current measurements, but the hydraulic regime associated with shoreface ridge genesis has not yet been adequately delineated. The detached ridges on the inner shelf may continue to respond to the wind- generated currents during storms, while in the deeper water of the central and outer shelf, a geostrophic component of flow, induced by set-up against the coast, may become important (Swift et al., 1972b). In order to evaluate the relationship between the ridge and swale topog- raphy of the central New Jersey continental shelf and the shelf hydraulic regime, and to gain additional insight into the evolution of the Holocene transgressive sand sheet, a detailed study was initiated in the summer of 1972. This study is one of several detailed studies being conducted along the continental margin of Eastern United States as part of the NOAA's MESA project, by the Atlantic Oceanographic and Meteorological Laboratories of Miami, Florida. Data for the central New Jersey shelf study consists of bottom grab samples, cores, sub-bottom profiles, side-scan sonar profiles, submersible dives, and current-meter data. The submersible dives were part of the Manned Undersea Science and Technology (MUST) office program of NOAA. The present paper will report on storm-generated bedforms as inferred from side-scan sonar records and submersible dives, and will discuss the implications of this evidence for the origin of the ridge and swale topog- raphy on the central shelf. METHODS Side-scan sonar runs were conducted with a Westinghouse high-resolution system which was towed at depths of about 10 m from the bottom at about 9—10 km/h. This system operates at 150 kHz frequency and maps a strip about 120 m wide; 60 m on each side of the ship's track. Sweep time for the transducer is 0.08 sec, and the signals were recorded on chart paper 48 cm wide with a chart advance of 8.44 inches/min. Bathymetric profiles were run together with the side scan, and navigational fixes were recorded every 5 min. Navigation was provided by Loran A system and fixes were adjusted to major aspects of bottom topography on the ESSA 999 HI bathymetric chart 0807 N-55. The laterial exaggeration present on the charts was reduced to true scale manually. Submersible dives (four on the central shelf and one on the inner shelf) were conducted with the Westinghouse Research Submersible "Deepstar 2000". Dive traverses were conducted across topographic trends, and bottom photographs and visual information were recorded along the dive profile. REGIONAL MORPHOLOGY (FIRST- AND SECOND-ORDER RIDGE SYSTEMS) Initial insight into the nature of the morphology of the New Jersey continental shelf was provided by the 1 -fathom maps of Veatch and Smith (1939) at a scale of 1:120,000. ESSA bathymetric charts of the shelf added considerable detail to the nature of the shelf morphology at a scale of 1:25,000 and with a 1-fathom contour interval (Stearns, 1967). Using the ESSA charts for the New Jersey shelf, McClennen and McMaster (1971) 40°N 39° 38c ' d i £L jL 75°W 74° 73° Fig.l. Major topographic elements of the New Jersey shelf. 1000 82 39° 00' N\ ' 38° 45' N\ < SCARP / — 7V 74°00'W 7 — 73°45'W CRESTLINES, SECOND ORDER HIGHS a W$ii FIRST ORDER HIGHS identified eight erosional-depositional surfaces, correlated them with similar shoreline forms on the Texas shelf, and suggested an origin related to sea- level changes. Swift et al. (1972b), again using the ESSA charts, outlined and discussed the distribution and evolution of large-scale morphologic elements on the central and southern Atlantic shelf. Major transverse valleys divide the New Jersey shelf into broad interfluves, whose surfaces tend to bear a subdued ridge and swale topography. Shelf 1001 83 73°45'W Fig. 2. a. Great Egg Shoal-Retreat Massif and study area. b. Detailed bathymetry of Great Egg Shoal-Retreat Massif. Contour interval 2 fathoms. From ESSA bathymetric chart 0807N-55. valleys are often paired with shelf transverse highs on their north sides (Fig.l). These shoal-retreat massifs mark the retreat paths of littoral drift depositional centers found on the north sides of estuary mouths (Swift etal., 1972b). This paper describes the Great Egg Shoal-Retreat Massif, extending from 1002 84 the vicinity of Atlantic City, New Jersey across a 27-m (13 fm) and a 37-m (20 fm) terrace, towards the central shelf (Figs.l, 2). Two orders of ridges can be recognized on the seaward end of the massif: (1) a first-order system of larger ridges with trends of 53° to 57°. The larger of the first order ridges form an irregular Z-shaped pattern (ridges A, B, C, and D of Fig. 2a). They are about 6 km (3 n.m.) apart, have widths of 2—6 km (1—3 n.m.) and exhibit 10—20 m of relief. A smaller set of first- order -ridges can be found seaward of the larger ridges (southeast of ridge C) which have dimensions and spacing similar to the inner shelf ridges. The second-order system of ridges and troughs has a regional extent which is closely related to the 37-m terrace. Its shoreward and seaward limits are coincident with the edges of the 37-m terrace, whose inner scarp is the Mid- Shelf Shore of Swift et al. (1972b) and the Block Island Shore of Emery and Uchupi (1972). The development of the second-order system occurs on the Great Egg Massif, and is largely lacking on the 37-m terrace to the north- east and in the shelf valley to the southwest. Ridges of the second-order system have, in general, closer spacing and smaller relief than the first-order ridges; 2—5 m high, 0.5—1.5 km apart. The second-order system is super- imposed on the first-order ridges and troughs in a variety of relationships. Swift et al. (1972b) have discussed the probable origin of the first- and second-order ridges for this portion of the shelf. The first-order ridges to the northeast on the 37-m terrace exhibit profiles which are compatible with an overstepped-barriers origin for these large ridges. To the southwest, the ridges no longer exhibit such profiles and have the characteristics of large estuary mouth shoals (Swift, 1971; Swift et al., 1973) suggesting an increased degree of modification of the ridge fabric by the Holocene hydraulic regime near the estuary mouth. The second-order ridges are closely associated with the margin of the massif on the 37-m terrace and are superimposed over the first-order ridges. They may reflect the transition from an inner to a deeper shelf regime, attendant on the resumption of the transgression after the 37-m stillstand. As sea level rose, the first-order ridges became isolated and may have been too large and widely spaced to respond to the new regime. SIDE-SCAN PATTERNS Interpretation of the record Side-scan records were interpreted on the basis of the variation of sonic signals with bottom-sediment types and bedforms (Belderson et al., 1972) and from particular knowledge of the bottom gained from submersible observations, cores and grab samples (Stubblefield et al., 1974) collected within the study area. The following patterns were recognized. (1) Granular pattern — indicates a sandy bottom with an irregular surface. (2) Granular with system of short-crested light and dark lined pattern — sandy wave-rippled bottom. 1003 85 (3) Dark pattern — coarse sand or gravel; in some cases the dark correlates with a shelly-gravel capping of a clayey substrate. The coarser pattern may also show a rippled surface. (4) Very light pattern — very fine sand. This fine sand is generally associated with the margins of some of the darker (coarser) bands and patches and represents return from a smooth surface. Alternation patterns of light and dark represent variations of signal return in response to slope incidence and shadow effect from relief features on the bottom as in the wave-rippled pattern. However, most of the dark and light patterns on the records reflect textural variation as described above and not relief. Sanders et al. (1969) describe the nature of side-scan records from selected study areas on the eastern U.S. shelf and correlate them with sub- mersible observations. The wave-rippled pattern is ubiquitious over most of the bottom. Two other types of patterns are mapped from the side-scan records: (1) a wide- spread pattern of elongate sediment bands (lineations), and (2) broad dark, single or double bands in troughs believed to represent outcroppings of the Holocene Pleistocene "basement" units. Representative examples of the side-scan records are presented in Figs. 3— 6. Third-order elements (current lineations) The side-scan records for the central shelf reveal a ubiquitious pattern of sets of elongate bands of contrasting sediment types. In general, this lineation consists of bands or patches of coarser sediment within a back- ground of wave-rippled finer sand. In some cases, broader zones of coarse sediment consist of small-scale ribbon-like alternations of fine and coarse sand. These ribbons may trend obliquely across the broad coarser zones. Although the boundaries between the sediment types are often irregular, the elongate nature of the series of sediment zones is evident. Representative examples of the lineations are shown in Figs. 3, 4 and 5. The regional variation in lineations and their morphologic aspects is illustrated in Fig. 9. The most dramatically developed lineation patterns are those developed in troughs (22—24 fathoms; 13.1—14.3 m) near the southwestern margin of the study area (Figs. 3, 4). At location A (Fig.7) a zone of alternating bands of gravel and sand is displayed in the base of any asymmetrical trough (Fig. 3c). The zone trends along the axis of the trough, while the bands trend obliquely across the zone. Bands are 10—14 m wide in general, with gravel being more represented along the deeper southwestern portions of the trough. The alternating sediment bands are well developed in the lower portions of the trough but are discontinuous and apparently partially erased as one approaches the ridge flanks. Wave ripples oriented north— south are present, with the coarser zones showing a sharper ripple pattern. Evidence from previous studies (Duane et al., 1972; McClennan, 1973) and from our submersible dives and cores, indicates that trough floors 1004 86 b <- 275 M, UJ O Fig. 3. a. Side-scan record of large-scale current lineations in trough. See Fig. 7 for location A. Helical vorticies have swept a thin fine-sand cover to reveal segments of the under- lying Pleistocene/Holocene "basement" in alternating patterns of coarse bottom furrows and sandy bands of ribbons. Note partial infilling of furrows on lower ridge flank to the NE. Scale is in meters. b. Corrected for lateral exaggeration. c. Cross section of profile. Lineations do not show relief. 1005 87 locally expose Pleistocene or Holocene lagoonal and backbarrier clayey sediments with a shell or gravel lag. It is suggested that the pattern of linea- tions displayed at site A has developed on an area where a thin sand cover over the gravel "basement" has been swept by elongated turbulent vortices to scour the thin sand cover and expose the gravel in the scour furrows between elongate sandy ribbons. The interrupted pattern on the ridge flanks suggests that the coarser furrows were initially developed over a wider area but have been subsequently partially obliterated. Maclntyre and Pilkey (1969) describe bottom features very similar to those suggested above from diver observations on the North Carolina shelf. The bedforms, located in about 20 m of water, consisted of a series of elongate channels or depressed patches of coarse calcareous sand and fine SE Fig. 4. a. Side-scan record of well-developed large-scale current lineations from a trough. See location B in Fig.7. Scale is in meters, b. Corrected for lateral exaggeration. 1006 gravel cutting across finer less calcareous sand. During a three-month observa- tion from June to August, 1968, ripple crests decreased in sharpness in the coarser sediment and were obliterated in the finer sands. Maclntyre and Pilkey (1969) suggest that the channels may have developed in response to the storm surge reflux related to Hurricane Abbey which passed the area on June 7 and 8th, 1968. Other trough lineation patterns are represented in Fig. 4 (B of Fig. 7). Fig. 4 illustrates a well-developed pattern of gravel furrows about 5 m wide with separations of about 18 m. No relief is associated with these forms. Fine sand occurs along the rim of some of the coarser zones. The en echelon arrangement of the gravel furrows may reflect the lateral limits of a zone which is characterized by a thin sand cover over the gravel substrate. Wave ripple patterns are especially well developed near the furrows. Similar but poorly resolved patterns are found associated with ridges locally and may have been subjected to smoothing by wave surge. 120 200 600 Fig. 5. Side-scan record of large-scale current lineations from ridge crest; location E, Fig. 7. Note planar asymmetry of lineations (sand patches). These forms showed heights of 1.5 m in profile. Scale in meters. The lineation pattern associated with the ridges shows a similar alternation of sediment types. In general, however, the pattern is not as sharply developed and gradational contacts are more common. Spacing is wider and relief to 1.5 m is locally developed in elongated sand patches (Fig. 9). The nature of the distribution of the morphological aspects of the lineation pattern will be discussed below. Fig. 5 (E of Fig. 7) shows a ridge crest pattern which is very 1007 89 similar to previously described sand patches (Belderson et al., 1972, fig.72). The sand patches have a spacing to about 75 m and heights to 1.5 m. Despite negligible relief, an asymmetry is locally discerned as a sharp boundary between sand and gravel on one side and a gradational one on the other. This type of asymmetry, where present, does not show a systematic pattern in relation to the larger morphologic elements. Locally the lineation series display J-shaped or U-shaped terminations especially on the ridge crests. These forms may represent remnants of transverse forms which became unstable during a later, more intense phase of the flow regime and were modified into longitudinal forms. Although not well developed, other forms appear to represent remnants of transverse sand wave forms. Locally the records suggest the presence of irregular lunate-like forms, somewhat degraded, within broader, elongate zones of coarser sand. These are compar- able to the lunate sand waves described as occurring within some sand ribbon zones from the North Sea (Kenyon, 1970). The lineations display a well-developed directional pattern across the study area. Fig. 7 shows the directional summaries of the lineation sets. The distinctive aspect of the lineation trends in relation to the second-order ridge trends is shown in Fig. 8. The lineation trend distribution appears to be 30° to 35° more easterly than that of the second-order ridge trend distribution. The trends of the second-order ridges within the side-scan study area fall within the central portion of the distribution between about 30° and 45° azimuth. The small mode of second-order ridge trend azimuths between 0° , and 15° west of north represents a series of small ridges which are transverse to and on top of the first-order ridge A near its southwestern terminus (Fig.2a). 'Busement" outcrop bands In addition to the side-scan lineation patterns another pattern can be recognized. Within the troughs the record displays very broad zones (to 150 m wide) of high reflectivity. This pattern correlates with exposure of Holocene/Pleistocene clayey units in the trough and trough flanks, often with a capping of coarse shelly debris (Fig. 9). A representative example of the record for these outcrop bands is given in Fig. 6a. The profile associated with the twin bands of location G is given in Fig. 6b. Such exposure of double bands on opposite sides of lower trough flanks was noted in several places and is believed to represent downcutting through the units. The bands are aligned parallel to the trough axis, in general, and do not follow the trends of the lineations. The association of the bands with troughs is shown in Fig. 9 where the location of the bands for the whole study area is given. 1008 90 1900 M Fig. 6. a. Side-scan sonar record of paired outcrop bands from lower trough flanks; location G, Fig.7. Scale in meters, b. Profile through location G showing position of outcrop bands and well-developed lineations (heights to 1.5 m) on second-order ridge. SUBMERSIBLE OBSERVATIONS AND SEDIMENT TYPES Insight into the distribution of sediment types from which the lineations are formed was gained from direct observations of the bottom from sub- mersible dives. Fig. 10 is a schematic representation of a submersible bottom survey which was run perpendicular to the trend of the topography (see Fig.7 for location of the traverse). Bottom sediment data from samples collected in adjacent areas (Stubblefield et al., 1974) has been projected on to the profile in their relative positions with respect to the topography and at the appropriate depth. Four categories of bottom type are recognized based on presence or absence of ripples, percentage and nature of shell material, and textural appearance of the sediment surface: 1009 91 39° 00' 73°55'W 73°50' Fig. 7. Map of study area showing average orientation of large-scale current lineation sets (heavy lines), tracklines of side-scan sonar survey with locations of Figs. 3— 6, and sub- mersible dive traverses (dotted lines). 2-fathom contour interval. A, —rippled bottom with shell fragments concentrated in the troughs; crests have fine-textured appearance and are armoured with sand dollars (Fig.lla). A2 — unrippled with scattered shell debris in moderate amounts, fine- textured surface and abundant sand dollars (Fig. lib). B — very smooth texture sediment surface and low percentage of scattered shell material (Fig. lie). C — very coarse shelly concentrate (Fig. lid). 1010 92 30-i 20 10- □ 2nd ORDER RIDGES Q3rd ORDER LINEATIONS AZIMUTH (°) Fig. 8. Histograms of orientations of large-scale current lineations (third order) and of crestlines of second -order ridges. The ripples were symmetrical, with broadly rounded tops. They were inferred to be degraded wave ripples. The largest and best developed ripples were located on the upper flanks and smaller more degraded ripples on the lower ridge flanks. This pattern probably reflects a grain-size gradient decreas- ing down the slope. The A2 zones, subjacent to the rippled bottoms may represent areas where ripples were once present but have since been completely degraded. The amount of coarse material (> 2 mm) is minor; generally less than 1% and consisting mostly of shell material. Fig. 10 shows the percentage of coarse material (> 2 mm) across the submersible traverse. Higher percentages of shell material appear to be associated with the better developed ripples on the upper flanks. In general, shell material from Aj and A2 zones consists mostly of Echinoid fragments; but locally on some higher parts of the ridge, razor clam (Ensis) debris appears more abundant. Bottom type B occurs on the lower flanks of the seaward portions of the two ridges. The sequence Ai — A2 — B can be explained as an effect of grain size decreasing downslope, with the very smooth B zone representing the depositional of fine material on the seaward portions of the ridges. This fine flank material of zone B may reflect the fallout of wave-winnowed sand from the ridge crests, or sand swept on to flanks from troughs. Zone C bottom may represent the outcropping of Holocene/Pleistocene shell-capped backbarrier units discussed above. These outcroppings are correlated with broad dark bands on the side-scan sonar records (Figs. 6a and 9). They occur in the broad portion of trough floors and in pairs, on the lower flanks of troughs. The percentage of coarse material is high (15—20%). Most of the coarse fraction consists of large pelecypods including Spisula, Pecten, and Crassostrea. The shells tend to be discolored, corroded, 1011 ;>:; 39° 05 39c 00 \(m) I 52-76 3 27-52 mmn >27 ■+- SHELL BAND CONTOUR INTERVAL : 2 FATHOMS a/w\ HEIGHT TO 1M 73°55 W 73°50' Fig. 9. Map showing areal distribution of morphologic aspects (spacing and height) of large-scale current lineations and locations of outcrop or shell bands. or riddled with fine bore holes. Some coarse clastic material including chert pebbles and reworked clay lumps is also present. A high percentage of the shells were concave upwards and many articulated shells were seen. No evidence of current sorting or alignment of shells was observed within the shell zones. 1012 94 KILOMETERS NW 1 2 SE A2. 1.5 - Mean 4> 1.6 -% > 1.0 mm. 36 40 44 UJ 48 52 Fig. 10. Bottom facies observed along submersible traverse X. See Fig. 7 for location. A, — fine-textured, wave rippled bottom with sand dollars (on wave crests) (Fig. 11a) A2 — fine-textured, unrippled bottom with sand dollar pavement (Fig. lib); B — very fine-textured smooth bottom (Fig. lie); and C — very coarse shelly gravel (Fig. lid). MORPHOLOGY OF LINEATIONS: HYDRAULIC INFERENCES The distribution of lineation sets, their spacing and relief is summarized in Fig. 9. The lineations are not well represented on ridge crests, especially the broad first-order ridge. Most of the lineation sets have spacings which fall into an intermediate class (27—52 m). These are commonly associated with ridge flanks and some ridge crests where the ridges are narrow. Closer spacing is characteristic of the troughs (< 27 m), while the widest spacing (52—76 m) is generally associated with ridge flanks and crests. Some inter- mediate and wide sets have relief from 1 to 1.5 m associated with them. A variety of linear sedimentary bedforms have been described in the literature. Allen (1966, 1968) has reviewed the available data on sand ribbons and similar forms. More recently, Kenyon (1970) has reviewed the subject in connection with the features of the North Sea sand-ribbon field. In the North Sea, ribbons of sediment up to 15 km long and up to 200 m wide extend parallel to the bedload transport paths of the strong tidal currents (surface currents of 2 knots — 100 cm/sec). The sand ribbons are only a few centimeter thick and are in transit across a veneer of lag gravels and coarse shell detritus. The ribbons can be placed into the following regional framework of bottom types as related to decreasing velocity of the tidal currents and variations in the nature and supply of sediments: (1) zones of sediment scour, (2) sand -ribbon zone and sand deposits, (3) sandy deposits over shelly gravel and (4) muddy deposits (Belderson et al., 1971). Within zone 4, elongate or transverse patches of sand to 2 m thick rest upon the basal transgressive conglomerate. Flemming and Stride (1967) describe such patches near Plymouth, England. The patches are less elongate than the ribbons and are associated with weaker peak velocities. 1013 95 The linear bedforms occurring on the central New Jersey shelf are similar to the elongate patches of the North Sea but locally may have dimensions comparable to the ribbons. Imbrie and Buchanan (1965) used the term large- scale current lineations to describe elongate bedforms in the Bahamas from water 4—7 feet deep (1.2—2.1 m). The bedforms were 50—100 feet wide (15.2-30.5 m) and over 1000 feet long (305 m) and a few feet high (< 1 m). They suggested that the lineations were a response to hurricane surge. Newton et al. (1973) report longitudinal features from side-scan studies of ,the West African shelf which are very similar to those of the central New Jersey shelf. Allen (1966, 1968) reviewed the hydraulics of sand ribbons and related forms and showed that they occur in a wide range of flow state and flow roughness. He attributes their formation to a helical structure in the flow field. Vortices with axes parallel to the main flow direction occur in pairs, one left-handed and one right-handed. The common descending limb of the vortex pair carries high-velocity water toward the bottom; adjacent rising limbs return slower bottom water to the surface. Scour generates troughs beneath the bottom current divergences of the common descending limb of a vortex pair, while deposition forms the elongate sand bedforms beneath the bottom current convergences of adjacent rising limbs. Wilson (1972) speculates that all longitudinal bedforms, whether deposited by wind or by water, are initiated by helical flow. Helical flow has been thought to be initiated by spacial heterogeneity in the distribution of suspended sediment (Vanoni, 1946). However, helical flow structure occurs in the absence of suspended sediment or a mobile bottom (Tanner, 1960), and appears to be inherent in turbulent flow fields (Nemenyi, 1946), perhaps as a consequence of unequal turbulent stress components (Allen, 1970). Brown (1970) demonstrates by stability analysis that the planetary boundary layer of the atmosphere consists of a modified Ekman velocity profile stabilized by helical flow cells. The helical cells occur as perturbations on the mean large-scale flow and may be oriented at an angle to the main geostrophic flow. Sand ribbons and similar forms are characterized by stream-transverse differences in bottom roughness due to the alternating bands of contrasting sediment types. Such roughness variations may tend to maintain the helical flow by producing transverse instability in the flow (Allen, 1966, 1968). Allen (1966) has suggested that if the whole flow were involved in the helical flow, the width/depth ratio of the flow would determine the spacing of the cells. However, Kenyon (1970) relates variation in the spacing of the ribbons of the North Sea to position within the regional velocity gradient and to the supply of finer, mobile sand, rather than to depth. He notes that closer-spaced ribbons occur in the higher velocity regions where material is predominantly in transit and there is a deficit of the mobile bedload sizes. Further down the velocity gradient, where, due to increased deposition, a greater portion of the mobile bedload sizes is available, ribbon spacing and size increases. Yet, further down the velocity gradient, where the entire bed 1014 96 1015 97 Fig.ll. Representative bottom photographs from submersible traverse. a. Facies A, — wave ripples oriented N— S with sand dollars capping crests and shell detritus in troughs. b. Facies A2 — unrippled, fine-textured bottom paved with sand dollars and scattered shell detritus. c. Facies B — very smooth, fine-textured bottom. Fewer shells. d. Facies C — coarse shelly gravel composed of mostly large pelecypods in concave upward positions. Shells are coated with fine sediment. Note presence of crabs and sponges. 1016 98 consists of mobile bedload sizes, the fields of transverse sand waves are developed. Allen (1966, 1968) has also noted that ribbon-like forms in general appear to be characterized by flow in which there is a deficit of sizes predominantly in motion. The increase in spacing noted in the North Sea may thus reflect the increased availability of the mobile bedload sizes due to the decrease in velocity down the velocity gradient and perhaps to the velocity gradient itself. Recently, Folk (1971) has been able to model helical flow related to longitudinal dunes by a rolling technique over a grease-covered glass plate. The movement in the atmospheric boundary layer and the grease patterns closely correlate with the patterns, spacing, tuning fork junctions, etc., of the dunes. It was shown that thicker grease areas produced wider and higher ridges. On the New Jersey shelf, it seems unlikely that the whole flow is involved in the formation of the third-order forms, since the water depth is much greater than the bedform spacing. In fact, the slight variations in depth show an inverse relationship; the wider spacing occurs, in general, in the shallower water of the ridge crests and flanks. The variations in the morphological aspects of the lineations as shown in Fig. 9 appear to reflect differences in the thickness of the bed material which is responding to the helical flow, that is, the local availability of the bedload material predominantly in motion. It would appear that the flow regime which produced the lineations was one which tended to entrain fine sand as the most mobile bedload material. In the troughs where the mobile bed material was a thin layer of fine sand over an immobile coarse "basement", the lineations are closely spaced and show no detectable relief. Up on the fine sand flanks and crests, the helical flow structure has encountered a thicker and more responsive bed environment and the lineations are, as a result, more widely spaced and higher (Figs. 9 and 6b). Similar variations in ribbon spacing have been observed between adjacent trough and flank areas of North Sea sand waves (Kenyon, 1970 fig. 7). It is noteworthy that there is a distinctly low frequency of lineations on some crestal areas, most notably the broad first-order ridge to the west. This ridge is characterized by coarser grain sizes than second-order ridges to the southeast (Fig. 10). It would thus seem that the nature of the bed material has been an important control on the nature of and presence or absence of the third-order lineations. The driving mechanism for the helical flow on the western European shelf is clearly the strong currents generated by the semi-diurnal tidal wave. Tidal currents on the New Jersey shelf are too weak (Redfield, 1956) to transport significant quantities of sediment, as is the southerly fair weather drift (Miller, 1956). Instead, bottom-sediment transport on the middle Atlantic shelf appears to be induced by the intense northeast winds associated with winter storms and hurricanes (Swift et al., 1972b). On the inner shelf these forces probably result in a flow field dominated by southward wind drift currents constrained by the shoreline. In the deeper water of the central and outer shelf, a geostrophic component of flow, induced by wind set-up against the coast, may become important. 1017 99 Smith and Hopkins (1972) report a similar regime on the Washington shelf. Summer current velocities of up to 40 cm/sec to the southwest at 1.5—2 m off the bottom have been recorded by McClennen (1973) in our study area during a mild summer "Northeaster". The current direction as inferred from the third-order features in the study area is more westerly than the south-westerly geostrophic flow for this area. It is believed that the lineation trend represents a response to the flow field of an intense storm, perhaps one with a considerable storm surge com- ponent. The study area is located near the boundary of the inner and central shelf. Previous work has indicated that it is indeed the fine sand fraction that is the most mobile constituent in relation to the unmixing of the shelf surface by these modern hydraulic agents (Swift, 1969, pp. 5/12— 5/14). Donahue et al. (1966) describe a thin coating (15—60 cm thick) of fine sand from a traverse across the New Jersey continental shelf as representing the reworked shelf sediments. Analysis of bimodal sand distributions from the outer Long Island shelf by McKinney and Friedman (1970) showed that the fine sand component had been moved across the outer shelf and mixed in with the coarser basal sands. From a coordinated study of sediments and bottom current measurements over a two-year period on the Washington shelf, Smith and Hopkins (1972) concluded that significant sediment transport occurs only during severe storms and that the net movement of bedload is negligible (100 m/year for fine sands) compared to suspension transport of silt (80 km/year). Such in-situ winnowing of the shelf surface and differen- tial transport of the fine sand fraction are important aspects of the first step in the return to grade of the shelf (autochthonous grading; Swift, 1970). RIDGE MAINTENANCE We tentatively infer that the third-order bedforms detected from the side- scan sonar investigation of the central New Jersey shelf are mesoscale longitudinal elements produced as a response to the hydraulic regime of a major shelf storm or storms. The third-order elements appear to reflect a helical flow structure. However, no evidence for a larger-scale helical flow structure has been found to date. The current trends of the lineations indicate that the storm that produced them swept obliquely across the trends of the large ridge systems. This oblique attack, or perhaps a sequence of such attacks, has apparently moved fine sand out of the troughs and up on the ridge flanks, where the fine sand may be stored in the larger depositional elements. Subsequent down-ridge movement of fine sand may be accomplished by wave reworking between major storms. This wave reworking of ridge crestal areas and down-slope movement would produce the partial obliteration of the storm-generated furrows on the lower ridge flanks noted above. Such down-slope movement and infilling would eventually coat the coarse trough pavement once again with fine sand. 1018 100 The trough-to-ridge transport of the fine sand fraction during storms may be an important aspect of the maintenance of the shelf ridge and swale topo- graphy. Over a period of years the ridges may be attacked from various directions by storm currents. Opposite sides of the ridges may receive a sweeping action by such variable oblique attacks. Storm attacks that are parallel to the ridge trends would also be effective in building and sharpening the ridges, if conjunct with a large-scale helical structure in the flow field. Smith (1969) describes a system where rotating tidal currents are able to maintain a ridge of complex geomorphic history. The ridge is maintained parallel to the mid-tidal flow with sand being swept first up one side and then up the other by the alternating tidal components. Shelf sectors such as the study area should be repeatedly surveyed to determine the extent to which the orientation of current-lineation sets vary. As suggested above, the first- and second-order ridge systems may have originated as a response to Holocene inner shelf hydraulics; with the first- order system perhaps inheriting aspects of dimensions and spacing from an older topographic fabric. These ridges may have been maintained through the action of modern shelf storm flow which has produced a pattern of large- scale current lineations of low relief on the shelf surface. REFERENCES Allen, J. R. L., 1966. On bedforms and paleocurrents. Sedimentology, 6: 153—190. Allen, J. R. L., 1968. Current Ripples. North-Holland, Amsterdam, 433 pp. Allen, J. R. L., 1970. Physical Processes of Sedimentation. 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Smith, J. D., 1969. Geomorphology of a sand ridge. J. Geol., 77: 39—55. Smith, J. D. and Hopkins, T. S., 1972. Sediment transport on the continental shelf off of Washington and Oregon in light of recent current measurements. In: D. J. P. Swift, D. B. Duane and O. H. Pilkey, (Editors), Shelf Sediment Transport: Process and Pattern. Dowden, Hutchinson and Ross, Stroudsburg, Pa., pp.143— 178. Stearns, F., 1967. Bathymetric maps of the New York Bight, Atlantic Continental Shelf of the United States, scale 1:125,000. National Ocean Survey, National Oceanic and Atmospheric Administration, Rockville, Md. Stubblefield, W. L., Lavelle, J. W., McKinney, T. F. and Swift, D. J. P., 1974. Sediment res- ponse to the present hydraulic regime on the central New Jersey shelf. J. Sed. Petrol, (in press). Swift, D. J. P., 1969. Outer shelf sedimentation: processes and products. In: D. J. Stanley (Editor), The New Concepts of Continental Margin Sedimentation. American Geological Institute, Washington, D.C., pp. 5/1— 5/26. Swift, D. J. P., 1970. Quarternary shelves and return to grade. Mar. Geol., 8: 5—30. Swift, D. J. P., Sanford, R. B., Dill, Jr., C. E. and Avignone, N. F., 1971. Textural differentiation on the shore face during erosional retreat of an unconsolidated coast, Cape Henry to Cape Hatteras, western North Atlantic shelf. Sedimentology, 16: 221-250. Swift, D. J. P., Holliday, B., Avignone, N. and Shideler, G., 1972a. Anatomy of a shore- face ridge system, False Cape, Virginia, Mar. Geol., 12: 59—84. 1020 102 Swift, D. J. P., Kofoed, J. W., Saulsbury, F. P. and Sears, P., 1972b. Holocene evolution of the shelf surface, central and southern Atlantic shelf of North American. In: D. J. P. Swift, D. B. Duane and O. H. Pilkey, (Editors), Shelf Sediment Transport: Process and Pattern. Dowder, Hutchinson and Ross, Stroudsburg, Pa., pp.499— 574. Swift, D. J. P., Duane, D. B. and McKinney, T. F., 1973. Ridge and swale topography of the Middle Atlantic Bight, North American; secular response to the Holocene hydraulic regime. Mar. Geol., 15: 227—247. Tanner, W. F., 1960. Helicoidal flow, a possible cause of meandering. J. Geophys. Res., 65: 993-996. Vanoni, V. A., 1946. Transportation of suspended sediment by water. Trans. Am. Soc. Civ. Eng., Ill: 67-102. Veatch, A. C. and Smith, P. A., 1939. Atlantic submarine valleys of the United States and the Congo submarine valley. Geol. Soc. Am. Spec. Paper, 7, 101 pp. Wilson, I. G., 1972. Aeolian bedforms — their development and origins. Sedimentology, 19: 173-210. 1021 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration Environmental Research Laboratories NOAA Technical Memorandum ERL AOML-21 AN AUTOMATED RAPID SEDIMENT ANALYZER(ARSA) Terry A. Nelsen Marine Geology and Geophysics Laboratory Atlantic Oceanographic and Meteorological Laboratories / w \ Miami, Florida May 1974 \„ 1022 DISCLAIMER The NOAA Environmental Research Laboratories do not approve, recommend, or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to the NOAA Environmental Research Laboratories, or to this publication furnished by the NOAA Environmental Research Laboratories, in any advertising or sales promotion which would indicate or imply that the NOAA Environmental Research Laboratories approve, recommend, or endorse any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NOAA Environmental Research Laboratories publication. 1023 CONTENTS Page ABSTRACT 1 INTRODUCTION 1 ARSA COMPONENT HARDWARE 3 DATA ACQUISITION AND COMPUTATIONAL PROGRAM 7 ARSA CALIBRATION 9 ARSA PERFORMANCE 17 SPECIAL TECHNIQUES 22 DISCUSSION AND CONCLUSIONS . 24 ACKNOWLEDGMENTS 25 REFERENCES 26 1024 AN AUTOMATED RAPID SEDIMENT ANALYZER (ARSA) Terry A. Nelsen ABSTRACT The ARSA (Automated Rapid Sediment Analyzer) is a pressure transducer grain-size analysis system. This basic Woods -Hole -type fall tube was automated by the addition of a digital voltmeter, Hewlett-Packard 9810A calculator, and an X-Y plotter. Eight minutes after sample introduction, the system automatically produces size distribution data in 0.25-cf) intervals, distribution statistics, and a plotted frequency histogram. Calibrated against sieves to provide compatibility with traditional techniques, the phi means produced by sieving and ARSA analysis showed no significant difference at the 95-percent confidence level. Precision checks of the system showed a maximum variation of ±0.05 for sample mean. Other statistical parameters such as standard deviation, skewness, kurtosis, and modal class were also strikingly similar. INTRODUCTION Historically, the most universally used technique for the segregation of sedimentary particles into arbitrary class intervals has been sieving. In the geological sciences, this technique has been applied to the textural analysis of sands for use in the study of natural sedimentary processes. When done carefully, sieving can nor- mally yield precise data. However, Ludwick and Henderson (1968) have pointed out the potential systematic errors in sieving of up to l-<}> class as a function of particle shape. The time consumed by obser- ving proper sieve loading, shaking durations, and accurate recovery and weighing of 21 0.25-<}) intervals can take up to several hours per sample. Large projects involving textural analyses therefore can ■ 1025 consume inordinate amounts of time or yield poor quality data as the result of the shortcutting of proper techniques. As early as 1938, Emery (1938) worked with an alternative to traditional sieve analysis. His technique allowed grains to fall through a water-filled settling tube and measured the height of sand accumulation in the tube versus time. His technique took about 5 min, a significant time improvement over sieving. Since then, other workers have modified his design (Poole, 1957) or introduced funda- mental modifications by measuring pressure changes in the water column with the transit of falling grains (Zeigler et aL . , 1960; Schlee, 1966) Bascomb (1968) introduced a variation on this theme, using a manometer and capacitance transducer, while Felix's (1969) system, modeled after earlier Dutch work, measured the accumulated weight of sediment on a balance pan as a function of time. Concepts such as "nominal diameter," "sedimentation diameter," and "equivalent diameter," clearly discussed by Sengupta and Veenstra (.1968), contribute to the moot point of correlating sieving and settling tube data. However, the above cited workers have construc- tively contributed to a reduction in time and labor involved for the textural analysis of sands. It should be noted that each of the abovementioned settling- tube techniques requires the human interpretation of analog strip- chart records. The reduction of analog strip-chart data using over- lay templates is subject to errors arising from drafting errors and 1026 misalinement of the template. Equally significant are human bias and judgment in data point picking. This cannot only be a function of fatigue, but can vary significantly from worker to worker. It is therefore desirable to have a Rapid Sediment Analyzer (RSA) which is as fast as those previously built and also yields highly accurate (relative to sieves) and precise data by eliminating the human element from the time of sample introduction to final statistical treatment of the data. A computer-based data acquisition system, coupled to a Woods -Hole -type RSA incorporating modifications suggested by Rayfield (1967), was developed and is hereafter referred to as an Automated Rapid Sediment Analyzer (ARSA) . ARSA COMPONENT HARDWARE The fall tube used in this system is clear plastic and has an inside diameter measurement of 10 cm and a total length of 200 cm. Pressure ports are located at 0.5 and 133 cm below the water level in the tube. This separation is dictated by the damping time of water surface oscillations resulting from sample introduction. Pressure and pressure changes within the water column are detected by a Hewlett- Packard Model 270 differential gas-pressure transducer and are inter- preted as voltage changes resulting from the displacement of the trans- ducer diaphragm. This analog voltage signal is conditioned by a Sanborn (Hewlett-Packard) Model 350-1100C carrier preamplifier before it is sent to a Hewlett-Packard Model 3480B digital voltmeter (with Model 3482A DC range unit) where it is transformed into a digital 1027 voltage signal. A Hewlett-Packard 2570A coupler/ controller with crystal clock provides a reference time base for the calculator's predetermined 0.25-cJ) fall times described in detail later. The coupler/ controller also provides electronic compatibility between the digital voltmeter and the calculator memory. The memory- calculation function of this system is provided by a Hewlett-Packard Model 9810A calculator. Final histogram display is generated on a Hewlett-Packard Model 9862A plotter. Total system compatibility dictated the exclusive use of a single electronics system. As pictured in figure 1, the fall tube is suspended from a wooden frame by metal turnbuckles with foam rubber separation pads. This minimizes vibration transmission to the tube -mounted transducer. Spirit levels secured to the fall tube at right angles insure a per- fectly vertical tube orientation through turnbuckle adjustments. Approximately 150 to 200 samples can be run before accumulated sedi- ment must be removed through the bottom drain valve and the tube re- filled with deionized or distilled water. The entire system is shock - mounted from the floor by additional foam pads. Figure 2 shows the sample introduction device. A controlled electric motor mounted above the tube depresses a sediment-coated screen onto the surface of the water column. The inverted sub-62 micron screen holds the sample in place (as seen in fig. 2A) by water surface tension. Parallel contact of the sediment-laden screen and the water surface releases the particles and permits a gentle and simultaneous discharge of the grains. 1028 Figure 1. Total view of ARSA fall tube, stand, and sample introduction device. 1029 Figure 2. (A) Showing variable- speed sample introduction device, top of fall tube, and upper transducer pressure port; and (B) Sample intro- duction device with sediment on screen ready for sample run. 1030 It should also be noted that line voltage fluctuation can introduce spurious transient signals into the system, causing erroneous voltmeter readings. It is therefore necessary to supply power through a voltage regulator. The entire system is pictured in figure 3. DATA ACQUISITION AND COMPUTATION PROGRAM A Hewlett-Packard Model 9810A calculator provides the heart of this ARSA data acquisition system. The calculator program includes subprograms for data acquisition, storage, computation, and hard copy output . Data acquisition starts when the sample introduction causes the baseline millivolt threshold to be exceeded. Based on fall-time values (to be discussed later) in the memory bank, the calculator then runs time comparison do-loops against the system's crystal clock. When the time value for each 0.25-<}) interval of the sand range (-1.00 to 4.00 ) is satisfied, the calculator commands the digital voltmeter to read the transducer voltage and to place this value in memory for future use in the data reduction subroutine. Successive voltage values decline in magnitude as grain fallout past the lower pressure port causes the transducer's diaphragm to return to the null (baseline) position. After gathering digital voltage values for all the 0.25- intervals in memory, the computational subroutine takes over. Statistics computed are frequency distribution, cumulative distribution, phi mean, standard deviation, sum of squares, skewness, and kurtosis. Except for the sum of squares, all computations are 1031 Figure 3. Total view of ARSA system showing fall tube and asso- ciated electronics . 1032 based on the moment statistical methods described by Krumbein and Petti John (1938). These values are presented in hard copy by the calculator printer. The graphic display is that of a 0.25-0 frequency histogram on the X-Y plotter. Examples of this graphic display are shown later in the memorandum. ARSA CALIBRATION Ten reference sands were sieved for grain-size distributions , using new 3-in. diameter (7.5-cm) sieves which had undergone micro- scopic examination for 2,100 warp and shoot measurements. Guided by the work of Shergold (1946) and McManus (1965), it was determined that a maximum of 20 g of sediment shook for 20 rnin yielded optimum sieving conditions. Bulk samples were split down to acceptable sieving size by a sample splitter and weighed to the nearest 0.01 g. After sieving, the preweighed sieves and their sediment loads were weighed to the nearest 0.01 g. Each 0.25--mean (trial I and II) Standard deviation Modal class 10-0-A 1.42, 1.39 1.00, 0.91 1.5, 1.5 FC2-8 2.66, 2.68 0.79, 0.73 2.5, 2.5 1F-A-1 2.01, 1.97 0.51, 0.54 2.0, 2.0 3A-C-1 2.76, 2.73 0.49, 0.47 2.5, 2.5 FC6-7 2.55, 2.56 0.52, 0.52 2.5, 2.5 FC11-1 2.92, 2.84 0.72, 0.75 3.25, 3.25 FC6-0 3.04, 3.03 0.33, 0.29 3.0, 3.0 FC6-2 3.44, 3.38 0.28, 0.28 3.25, 3.25 FC2-1 2.38, 2.39, 2.40 0.47, 0.48, 0.44 2.5, 2.5, 2.5 4-A-l 2.58, 2.60 0.60, 0.60 2.0, 2.0 1034 this system. Based on these times , multiple precalibration runs were made. They consisted of 4 to 5 g splits of the original 20-g sieve samples. The results of these runs are tabulated in table 2. A plot of sieving phi mean versus ARSA phi mean (a two-run average) for the 10 sample suite can be seen in figure 4. Regression analysis of these points yielded a slope value of 1.07 and a "Y-inter- cept" of -0.29. Using the relation $sieve . . = -0.29 + 1.07 • r & r equivalent ($ARSA), all the 0.25-$ intervals (-1.0 to "4.0 $) were substituted into the equation. The resulting $sieve . , values are recorded in table 3. A plot of these values versus fall times (table 3, in Hewlett- Packard units) yielded a series of phi-time curves from -1.37 to 4.0 $. Then by picking even 0.25-$ intervals from these curves (from -1.0 to 4.0 $), modified fall times were determined (table 3). Substituting these modified fall times into the calculator memory, additional splits of the sieved standards were run in the ARSA. The postcalibration means are tabulated in table 4, column B. Comparisons of the sieved column with column A (precalibration $ mean) and column B show that calibration has either resulted in no change to previous phi mean (six samples) or change toward the sieved mean values (four samples). How- ever, an unacceptable difference in character between the frequency distribution histograms for sieving (fig. 5A) and ARSA (fig. 5B-C) analysis is readily apparent. A "blip" occurs in the class between 3.5 and 3.75 $. If viewed not as a "blip" but as a distribution shoulder preceded by a "hole," it can be reasoned that the settling time allowed for the 3. 25- to 3.5-$ interval is too short, producing 1035 Table 2. Precalibration Runs on the ARSA of the 10 Reference Sands Sample 4>-mean Standard deviation Modal class 10-0-A 1.56, 1.58 0.95, 0.97 1.75, 1.75 FC2-8 2.75, 2.76 0.51, 0.58 2.75, 3.00 1F-A-1 2.21, 2.13 0.56, 0.53 1.75, 1.75 3A-C-1 2.77 0.37 2.50 FC6-7 2.67, 2.72 0.41, 0.40 2.50, 2.50 FC11-1 2.95, 2.98 0.54, 0.55 3.00, 3.00 FC6-0 3.13, 3.20 0.29, 0.26 3.00, 3.00 FC6-2 3.43, 3.43 0.26, 0.27 3.50, 3.50 FC2-1 2.50, 2.57 0.43, 0.40 2.25, 2.50 4-A-l 2.66, 2.65 0.53, 0.52 2.50, 2.25 1036 4.0 3.0 uj 2.0 > UJ CO £ 1.0 0.0 -1.0 -1.0 SLOPE ' 1.07 Y-INT. =-0.29 ' ' J I I I I L 0.0 1.0 2.0 PHI (ARSA) 3.0 j i Figure 4. Scatter plot of phi mean ARSA versus phi mean sieve with slope and Y-interaept values of the least-squares line. Table 3. Fall-Time Modification Values 0.25-c}) intervals ^sieveequivalent Modified fall times -1.00 -1.37 84.3 -0.75 -1.10 91.7 -0.50 -0.84 99.7 -0.25 -0.57 109.1 0.00 -0.30 121.0 0.25 -0.03 134.4 0.50 0.24 150.4 0.75 0.50 168.9 1.00 0.77 193.2 1.25 1.04 223.2 1.50 1.31 259.2 1.75 1.57 301.0 2.00 1.84 355.1 2.25 2.11 423.0 2.50 2.38 511.6 2.75 2.64 1,149 3.00 2.91 1,490 3.25 3.18 2,225 3.50 3.45 2,675 3.75 3.71 3,120 4.00 3.98 3,612 *4>sieveequivalent x -o .29 + 1.07 ($ARSA) 1038 Table 4. Precalibration and Postcalibration Phi Mean Values for Reference Sands Sample Phi ((f)) mean 10-0-A Sieve ARSA 1.41 A B C 1.48 1.46 1.40 FC2-8 2.67 2.57 2.57 2.65 1F-A-1 1.99 2.02 2.02 2.08 3A-C-1 2.74 2.71 2.71 2.74 FC6-7 2.55 2.49 2.54 2.57 FC11-1 2.88 2.87 2.87 2.83 FC6-0 3.04 2.94 3.02 3.05 FC6-2 3.41 3.26 3.28 3.26 FC2-1 2.39 2.43 2.43 2.48 4-A-l 2.59 2.54 2.54 2.55 1039 50 £ 40 > o 2 30 o uj 20 tr B 3* 10 0 -2.0 50 - 40 - 5 30 2 20 cr u. io H 0 -2.0 50 £ 40 >- o z 30 UJ 2 20 AC u. 10 - 0 -2.0 FC6-0 (SIEVE) PHI MEAN =303 STD. DEVIATION 0.29 SKEWNESS0.I4 KURTOSIS ' -0 02 x ' I Led I L, -1.0 0.0 1.0 2.0 3.0 4.0 5.0 PHI FC6-0 (ARSA) PHI MEAN = 2.99 STD. DEVIATION =0.26 SKEWNESS0.92 KURTOSIS -0.04 _L _L _L J„ Ln JL J -1.0 0.0 1.0 2.0 3.0 4.0 5.0 PHI FC6-0 (ARSA) PHI MEAN = 3.04 STD. DEVIATION =0.26 SKEWNESS=0.9I KURTOSIS =0.07 x X Ul JL ZL J -L0 0.0 1.0 2.0 3.0 4.0 5.0 PHI Figure 5. (A) A size frequency histogram of the sieve analysis of sand FC6-0; (B) a "calibrated" run of sand FC6-0 on the ARSA; and (C) a second run on the ARSA of sand FC6-03 showing a fine tail "blip" similar to "B. " 1040 this "hole" as an artifact. Figures 6A-G show the progressive re- running of sample FC6-0 with the manipulation of one to three class- interval time values. Figure 6G shows the final compromise and its relation to the sieved trial (fig. 6H). It is interesting to note that although the character of figures 6A and 6G differ drastically, the means differ by only 0.03 . Using these new time constants, the entire 10 sample suite was rerun yielding means tabulated in table 4, column C. Some examples of the final character of the ARSA histo- grams versus the sieve histograms can be seen in figures 7 and 8. ARSA PERFORMANCE The average sieve precision for phi mean in this 10 sample suite is ±0.02 cf>. For the final calibration of the ARSA, repetitive runs gave an average precision of ±0.04 $ with a maximum variation of ±0.05 cj). Table 5 compares phi means of sieved and ARSA samples as well as four other fundamental statistical parameters. Worth noting is the good agreement between higher moment values such as skewness and kurtosis, which, respectively, contain third- and fourth-power compo- nents. For this 10-sample calibration suite, the correlation of phi means for sieving versus ARSA is 0.99. In figures 6A-G, the character of the curves was purposely altered, as previously stated. However, the modal class is always at 3.0 to 3.25 and, with the exception of a few very small per- centages, the first class is always 2.75 to 3.0 4>. The range of phi mean is only ±0.03 <\> in seven runs. This test series represents 1041 A 60 50 £ 40 > <_> z uj zi o uj 20 - 30 10 - FC6-0 (ARSA) PHI MEAN 3 08 STD DEVIATION 0.28 SKEWNESS 0.61 KURTOSIS -0 86 v <_> z UJ O 0 -20 60 50 40 30 - 20 - 10 - -1.0 0.0 1.0 20 30 40 50 FC6-0 (ARSA) PHI MEAN 3.08 STD DEVIATION 0.27 SKEWNESS 0 61 KURTOSIS -0.72 >- o z UJ o 0 -20 60 50 40 30 20 - 10 - J L _1_ -1.0 0.0 1.0 2 0 3.0 40 50 FC6-0 (ARSA) PHI MEAN' 3.07 STD DEVIATION > 0 27 SKEWNESS 0.62 KURTOSIS -0.51 0 -2 0 J I i i_ Ul r> a 50 40 30 20 10 -1.0 00 1.0 2 0 30 40 5 0 FC6-0 (ARSA) PHI MEAN i 3.03 STD. DEVIATION 0.25 SKEWNESS 0.70 KURTOSIS -0.35 _| 0 -2 0 -1.0 0.0 1.0 20 3.0 4.0 50 PHI £ 60 r 50 ^ 40 >- o o uj 20 - o z 30 - u 2 20 ae u. 10 - J I I I c±A -10 0 0 10 2 0 3 0 4 0 5 0 FC6-0 (ARSA) PHI MEAN 3 05 STD DEVIATION 0 23 SKEWNESS 0.10 KURTOSIS 0.32 H UJ S 20 K 0 -20 50 40 - 30 I I I L ^L 10 - -1.0 0.0 1.0 2.0 30 40 50 FC6-0 (SIEVE) PHI MEAN 303 STD DEVIATION 0.29 SKEWNESS 0.14 KURTOSIS : -002 0 -20 1 -Lj^ L Ll 10 0.0 1.0 2.0 30 40 5.0 PHI Figure 6. Progressive "tuning" (A-G) of the ARSA to match the sieved (H) histogram. 1042 o z hi O UJ u. 50 40 30 20 10-0-A (SIEVE) PHI MEAN = 1.39 STD. DEVIATION = 0.91 SKEWNESS = -0.20 KURT0SIS'-0.40 B o z UJ 3 o UJ cc u. 50 10-0-A (ARSA) PHI MEAN< 1.40 40 STD. DEVIATION '0.93 SKEWNESS'-0.56 30 KURT0SIS'0.I3 20 10 n i rL-TT-r^\ , h-i . -2.0 -1.0 0.0 1.0 2.0 PHI 3.0 4.0 5.0 Figure 7. Final ARSA calibration check, comparing (A) sieved with (B) ARSA analysis of sample 10-0-A. 1043 50 _ 3A-C-I (SIEVE) 40 - <£ >- 30 UJ ID O LU ) particles, the samples are presized with sieves to eliminate the greater than -1.0- classes as well as the less than 1046 4.0-at v/r7 in- r^ 3.15 >M. <1> -7 LK AJ7 Wlr rJv >V A TTTTT 3.4 Mill 0- (Sea level) 5 10 15 20 25 - 30 35- 40 M M .1) \ - / ,. / \ » / * i \ » i^i \ - 2.8 ' * / \ - / - i \ » i*i \ > / ^ / XXX X XX 2.8 XXX x. x. K XXX 2.8 llll 3.3 llll M Till 3.3 llll llll 3.3 llll M s X-Ll >A> IfJ 3.15 A> s/ >A-7 r\^ a TTTTT 3.4 Inn Fig. 5. A. Crustal columns with densities in the western central North Atlantic (Worzel and Shurbet, 1955; Ewing and Ewing, 1959; Talwani et al., 1965). B. Crustal columns isostatically adjusted for removal of the water and sediment layers. M is the Mohorovicid discontinuity and is considered the level of compensation for isostatic computations which balance the water and sediment removed with mantle material (3.3— 3.4 gm/cm3 ). by the rate of sediment accumulation of the continental rise. Relatively fast transfer of sediment from the continental shelf to the continental rise would result in a relatively rapid rate of coupled subsidence of the continental rise and continental shelf; relatively slow transfer of sediment from the continen- tal shelf to the continental rise would result in a slow rate of coupled sub- sidence. Considerations of isostasy necessitate a subcrustal flow to compensate for the mass eroded from the continent (Lawson, 1932). A component of this flow may originate beneath a portion of the continent adjacent to the area of erosion. Another component of flow may originate beneath the adjacent 1064 292 continental shelf and ocean basin in response to the sediment load trans- ferred from the continent. The mass transfer may occur by ductile flow in the upper mantle toward the area of erosion involving crustal subsidence where the flow originates (Bott, 1964). Bott and Dean (1972) have used the finite-element method of stress analy- sis to show that the present distribution of density and elastic moduli in rocks underlying aseismic continental margins produces a differential stress system favorable to normal faulting in the upper continental crust, particu- larly in the region of the continental slope, causing local basinal subsidence and creep in the lower continental crust which results in crustal thinning by flow towards the sub-oceanic upper mantle. The thinning of continental crust seaward beneath the coastal plain and the continental slope off Cape Hatteras (Fig. 2) may reflect such continuous processes of mass transfer. Integrating the effects of various mass transfer processes, Gilluly (1964, p. 490) envisions the continental margin as a zone of seaward torque about a horizontal axis with: (1) the continent tending to flow out over the ocean floor; (2) the continental shelf being depressed by both this continental spreading and by the increasing load of sediment; and (3) a continent-trend- ing flow in the mantle compensating for the mass transferred. RELATION BETWEEN EPEIROGENIC SUBSIDENCE OF THE CONTINENTAL SHELVES AND OCEAN BASIN IN THE CENTRAL NORTH ATLANTIC Vogt and Ostenso (1967) incorporated the subsidence of continental shelves on rifted continental margins into the hypothesis of mid-ocean ridge formation by postulating that the shelves originate when a continental plate rifts over a pre-oceanic uplift. The original surfaces of the continental shelves are formed by erosional lowering to sea level of the continental crust in- volved in the uplift, thereby beveling the rifted edges of the continents, fol- lowed by progressive tilting seaward in response to continued vertical sub- sidence during horizontal movement away from the ridge axis. Sediment accumulation on the original shelf surfaces begins near sea level at the initia- tion of the seaward inclination and continues during subsidence below sea level. The subsidence is attributed to isostatic adjustment consequent on progressive subcrustal decrease in volume resulting from thermal contraction and phase change. Two conditions that can be readily tested follow from this hypothesis: (1) The upper surface of crustal layer 2 of the ocean basin, presumably generated by sea-floor spreading, would be expected to slope continuously landward from the Mid-Atlantic Ridge up to the continental shelf (for ex- ample, see Schneider and Johnson, 1970, fig. 14). As Menard (1969, p. 279) has pointed out, "It may be a general characteristic of moving plates that they slope continuously in the direction of motion." (2) The subsidence regime of the continental shelf should be the same as that of the ocean basin. 1065 293 To test condition 1 of the Vogt-Ostenso hypothesis, crustal columns con- structed from seismic refraction and gravity measurements were assembled at the Mid-Atlantic Ridge (30° N), the west basin, the continental rise, and the continental shelf off Cape Hatteras (Fig. 5). The top of crustal layer 2 of the ocean basin included in the 2.8 gm/cm3 density layer increases in depth below sea level between the Mid-Atlantic Ridge, the west basin, and the con- tinental rise (Fig. 5 A). However, if the isostatic load of sea water plus sedi- ment is removed and perfectly compensated at the Mohorovicic discontinu- ity, then the top of layer 2 increases in depth between the Mid-Atlantic Ridge and the west basin but, contrary to prediction, reverses slope and ascends about 800 m above the west basin at the continental rise (Fig. 5B). This observation is supported by the finding that the distribution of depth of the marginal basins in the North Atlantic follows a sine curve parallel to that of the ridge crest which decreases from a maximum elevation (minimum depth) near the pole of rotation of the two lithospheric plates bounding the ridge to a minimum elevation (maximum depth) at the equator of plate rota- tion (Rona, 1971, fig. 1). These observations indicate that processes of sub- sidence of oceanic crust about the Mid- Atlantic Ridge apply from the ridge crest to the marginal basins. However, processes additional to those invoked by the Vogt-Ostenso hypothesis are inferred to act landward of the west basin to account for the rise in crustal level beneath the continental rise. These additional processes may include the following: (1) Stress field between the continent and the ocean basin: The adjacent continental crust may exert a buoyant force, F^al, which interacts with a de- pressant force of the heavier oceanic crust, FsimSL, resulting in the potential 800-m rise in crustal level at the continental rise. This assumes a high degree of vertical coupling between continental and oceanic crust. (2) Physical properties of the crust: The continental rise off Cape Hatteras may be underlain by crust lighter than typical oceanic crust yet heavier than continental crust. This intermediate crust may be the product of magnetic differentiation soon after continental rifting at an early stage of sea-floor spreading or may result from complications associated with rifting. Asym- metry in the width of the magnetic quiet zone, which is nearly twice as wide off Cape Hatteras as off Cap Blanc, indicates that the mid-oceanic ridge as- sociated with the rifting of North America and Africa may have migrated or jumped eastward, leaving a relict ridge beneath the continental margin of eastern North America (Rona et al., 1970; Luyendyk and Bunce, 1973). Condition 2 of the Vogt-Ostenso hypothesis depends on the rates of sub- sidence of mid-ocean ridges with time, which are determined from the dif- ference in elevation between dated points on the ridge flanks (oceanic crustal layer 2) and the adjacent ridge crest, assuming that the flanks at each locality were once at the present depth of the crest. The average subsidence rates with time synthesized from all ocean basins are as follows (Menard, 1969): The rate of subsidence of oceanic crust about a mid-ocean ridge decreases with time after generation at the ridge crest as a function of the age of the 1066 0-10 9.0 (range 5—19) 10-40 3.3 (range 0—8.6) 40-70 2.0 70-140 2.0 294 Time interval Average subsidence rate of Amount of (10 year) mid-ocean ridge (cm/10 year) subsidence (m) 900 1000 600 1400 oceanic crust and reaches an apparent equilibrium of about 2.0 cm/103 year about 40 m.y. after generation. Models based on the process of thermal con- traction indicate that the rate of subsidence of oceanic crust spreading about a mid-oceanic ridge decreases exponentially with a time constant of about 50 ± 10 m.y., independent of spreading rate (Langseth et al., 1966; McKenzie, 1967; Sclater and Francheteau, 1970; Sleep, 1971). If constant sea level is assumed, the rates of sediment accumulation on the continental shelves of southeastern North America and northwestern Africa may be regarded as apparent crustal subsidence rates and compared with the rates of subsidence of oceanic crust, as follows: (1) Sediment accumulation on the original surface of the continental shelf at Cape Hatteras apparently did not begin until Late Jurassic (about 155 m.y. BP) (Fig. 3) after the initiation of active sea-floor spreading about 180 m.y. BP. This 25-m.y. lag may represent the time for an initial uplift to reach sea level and is compatible with the time constant of 50 ± 10 m.y. computed for the thermal contraction of a mid-ocean ridge (Sleep, 1971). Alterna- tively, the time lag may be due to the original rift between North America and Africa lying 150—200 km east of Cape Hatteras so that it took that length of time to begin sedimentation at Cape Hatteras (J. Gilluly, personal communication, 1973). (2) Late Jurassic through Recent (155—0 m.y. BP) average sediment ac- cumulation rates of the continental shelves at Cape Hatteras and at Cap Blanc, 2.0 and 2.4 cm/103 year, respectively, are compatible with an average subsidence rate of 2.0 cm/103 year of oceanic crust 40 m.y. and more after generation at a mid-ocean ridge. Sleep (1971) demonstrates with strati- graphic data from deep wells that the rate of subsidence of the Atlantic con- tinental margin of the United States decreases exponentially with a constant similar to that for the subsidence of oceanic crust about mid-oceanic ridges. (3) Evidence for an early shift in tilt axis off Cape Hatteras exists in the change in apparent inclination of the Paleozoic basement which occurs 130 km seaward of the Fall Line coincident with the apparent landward limit of Upper Jurassic (?) strata (Fig. 3). The angular rate of tilt about this axis from Late Jurassic to Early Cretaceous (155?— 135 m.y. BP; 0.508 • 10"7 deg./year) is nearly ten times faster than subsequent rates about the Fall Line, compatible with the relatively fast rates observed during the initial 40 m.y. of subsidence of oceanic crust (Fig. 6). 1067 295 0 KM 50 100 150 200 250 300 350 , — ,_, ,, , ,, , i, — < — ^—^ SEAWARD VERTICAL EXAGGERATION ABOUT 25:1 Fig. 6. Model to interpret the development of the marked change in inclination of the Paleozoic crystalline basement surface observed beneath the Hatteras coastal plain — con- tinental shelf (Fig. 3). A. A surface of erosion develops (on Paleozoic rocks) to form the original surface of the coastal plain— continental shelf. B. The surface of erosion tilts seaward by landward uplift and seaward subsidence about an axis perpendicular to the plane of the diagram (axis 1, Late Jurassic— Early Creta- ceous). Erosion occurs landward of axis 1 and sedimentary strata (Late Jurassic — Early Cretaceous) are deposited seaward of axis 1. C. The axis of seaward tilting shifts landward to axis 2 (post-Early Cretaceous) with a corresponding shift in the areas of erosion and deposition. The shift from axis 1 to axis 2 has resulted in a corresponding local epicontinental marine transgression. CONCLUSIONS The continental margins of southeastern North America and northwestern Africa were formerly conjugate, have rifted, and have drifted apart during the Mesozoic and Cenozoic as the intervening central North Atlantic ocean basin has opened and accreted by sea-floor spreading (Fig. 1). Development of the characteristic seaward thickening wedge of Mesozoic and Cenozoic sedimentary strata beneath the coastal plain— continental shelf of southeastern North America and northwestern Africa (Fig. 3) is con- trolled by seaward tilting of the original pre-Late Jurassic shelf surfaces by epeirogenic subsidence. Two categories of hypotheses attempt to explain the subsidence of rifted aseismic continental margins: 1068 296 (1) Isostatic adjustment in response to material transfer: These hypotheses attribute the shelf subsidence to isostatic adjustment consequent on crustal (Dietz and Holden, 1966; Bott and Dean, 1972) and/or subcrustal (Lawson, 1932; Gilluly, 1964; Van Bemmelen, 1966) material transfer by rock flow- age between the continent and the ocean basin. This line of reasoning implies that continental uplift and ocean basin subsidence are coupled in terms of a material balance effected through the processes of material transfer, if not coupled in the strict sense of vertical crustal coherence. The shelf tilts sea- ward in response to the adjacent opposing vertical adjustments of continent and ocean basin. (2) Isostatic adjustment in response to changes of material density in situ: These hypotheses attribute the shelf subsidence to isostatic adjustment con- sequent on increasing the density the oceanic crustal and subcrustal rocks by thermal contraction (Langseth et al., 1966; Vogt and Ostenso, 1967; McKenzie and Sclater, 1969; Sclater et al., 1971) and/or phase changes (Bott, 1964; Ringwood and Green, 1966; Beloussov and Kosminskaya, 1968; Elsasser, 1968; Sheridan, 1969; Sclater and Francheteau, 1970). This line of reasoning implies that the degree of vertical coupling between the continen- tal shelf and ocean basin is sufficient for shelf subsidence to be controlled by ocean basin subsidence — that is, the shelf tilts seaward as the outer shelf subsides as if coupled with the ocean basin. As radically different as these two categories of hypotheses are, at our present stage of knowledge, it is difficult to evaluate their relative impor- tance in the seaward tilting of rifted aseismic continental margins. Both rock flowage between the continent and ocean basin and in-situ increases in rock density are active processes that are reasonably inferred to have interacted throughout the development of the continental shelf. Each appears quan- titatively adequate to have produced the more-or-less continuous seaward tilting of the coastal plain— continental shelf. Both processes require the con- tinent and ocean basin to behave as if a relatively high degree of vertical coupling has existed between them even though fault systems are inferred to intervene between the continental interior and the continental shelf and the ocean basin. Seaward tilting of the coastal plain— continental shelf involves both subsidence of the outer continental shelf and uplift of the continent landward of the coastal plain. The subsidence of the outer shelf appears to follow the subsidence regime of oceanic crust, modified by the presence of crust underlying the continental rise off Cape Hatteras with characteristics intermediate between continental and oceanic (Fig. 5). The uplift regime of the continent adjacent to Cape Hatteras appears to have been more-or-less continuous throughout the tilting of the shelf (Gilluly, 1964). It is apparent that the seaward tilting of continental shelves on rifted aseismic continental margins should be treated as an ocean— continent system involving both material transfer and in-situ processes. 1069 297 ACKNOWLEDGEMENTS I thank R.S. Dietz and J. Gilluly for helpful reviews. This work is part of the Trans- Atlantic Geotraverse (TAG) of the National Oceanic and At- mospheric Administration (NOAA). 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Soc, 24: 325—350. Talwani, M., Le Pichon, X. and Ewing, M., 1965. Crustal structure of the mid-ocean ridges. 2. Computed model from gravity and seismic refraction data. J. Geophys. Res., 70: 341-352. Van Bemmelen, R.W., 1966. On mega-undations: a new model for the earth's evolution. Tectonophysics, 3: 83—127. Veatch, A.C. and Smith, P.A., 1939. Atlantic submarine valleys of the U.S. and the Congo submarine valley. Geol. Soc. Am., Spec. Pap., 7: 101 pp. 1071 299 Vogt, P.R. and Ostenso, N.A., 1967. Steady state crustal spreading. Nature, 215: 810—817. Walcott, R.I., 1972. Gravity, flexure and the growth of sedimentary basins at a continen- tal edge. Geol. Soc. Am. Bull., 83: 1845-1848. Worzel, J.L., 1968. Survey of continental margins. In: D.T. Donovan (Editor), Geology of Shelf Seas. Oliver and Boyd, Edinburgh, pp. 117—152. Worzel, J.L. and Shurbet, G.L., 1955. Gravity anomalies at continental margins. Proc. Natl. Acad. Sci., 41: 458-469. 1072 PETER A. RONA ROBERT S. DIETZ } National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratories, IS Ricken- backer Causeway, Miami, Florida 33149 Sediment Accumulation, Sea-Floor Spreading, and Eustacy: Reply Brown (1974) raised questions which lead us to consider the na- ture of unconformities in the stratigraphic record and the apparent absence of a Paleozoic record in ocean basins. It is useful to take a historic approach to sort out ideas on the nature of unconformities. Suess and Chamberlin recognized that eustatic fluctuations in sea level could be controlled by changes in the cubic capacity of ocean basins. Suess (1906) considered that, apart from certain local movements, the continental areas of the world have been absolutely stable through geological time, so that epicontinental marine regression resulting from eustatic lowering of sea level would produce synchronous world-wide unconfor- mities. In contrast, Chamberlin (1909) considered that continental areas of the world were subject to synchronous diastrophic move- ments that produced synchronous world-wide unconformities bounding the geologic periods. As cited by Brown (1974), the observation of Spieker (1946, 1949), that a surface of unconformity in central Utah does not coincide with the period boundary between Cretaceous and Ter- tiary, controverts Chamberlin's hypothesis of periodic diastro- phism and associated unconformities. However, the concepts of diastrophic cycles comprising asynchronous crustal movements and of synchronous world-wide unconformities, resulting from other than continental diastrophism, remain valid. Stratigraphic evidence indicates that certain unconformities are synchronous and world-wide. The evidence includes syntheses of cratonic stratigraphic sequences by Sloss (1963) and others, the correlation of unconformities on cratons with unconformities or decreases in average rates of sediment accumulation on subsiding continental shelves (Rona, 1973a), and with unconformities at sites in ocean basins (Rona, 1973b). The apparently synchronous and world-wide unconformities correlate with times of marine regres- sion attributable to eustatic lowering of sea level consequent primarily on increase in the cubic capacity of ocean basins (Suess, 1906). Diastrophism remains the ultimate basis of correlation, but this is oceanic diastrophism involving reversible volume changes of the mid-oceanic ridge system, as opposed to continental diastrophism (Chamberlin, 1909). Cyclic eustatic fluctuations of sea level, which result primarily from oceanic diastrophism, pro- duce world-wide epicontinental marine transgressions and regres- sions which are manifested in stratigraphic sequences separated by unconformities complicated by the interaction of eustatic and tec- tonic effects on unstable continents (Sloss, 1973; Rona and Wise, 1974). Brown apparently believes that Paleozoic deep-sea sediments may be present in the Deep Sea Drilling Proiect (DSDP) cores but are unrecognized for lack of fossils. We disagree. Paleontologists working with these cores have not as yet even recorded any possi- ble examples of a Paleozoic section (Terrence Edgar, 1973, oral commun.). Also, no thick, barren sequences have been encountered beneath the fossiliferous sediments which might be so interpreted. While it is true that most pelagic microfossils, capable of fossiliz- ing, evolved in the post- Paleozoic (for example, foraminifera, dis- coasters, coccoliths, siliceous diatoms), not all of them have. We suspect that Paleozoic deep-sea sediments, if present on the ocean floor, might reveal biostratigraphically useful radiolarians, dinoflagellates (cysts and thecae), acntarchs, palynomorphs, chitinozoans, conodonts, ostracodes, benthonic foraminifera, grap- tolites, problematica, and occasional macrofossils. Even if some of these are shallow-water benthonic forms, downward displacement by turbidity flows would carry them into the deep-sea realm. Of course, the pelagites may pose greater difficulty for identification than the turbidites. Most sediments overlying the ocean crust have undergone less diagenesis and low-grade metamorphism than sed- iments of equivalent age of the continents. The preservation of any Paleozoic fossils presumably would be good and their presence probably would not escape careful paleontological search. Cores into Paleozoic sediments from the abyss would certainly be sufficiently anomalous to arouse suspicion. Geological Society of America Bulletin, v. 85, p. 83 1 -832, May 1974 1073 A case in point, perhaps, is DSDP hole no. 4 off San Salvador in the Bahamas. This core encountered mid-Jurassic sediments — 155 m.y. old, as old as any sediments identified to date on the deep ocean floor. These sediments were too ancient to be identified by the usual microfossils, coccoliths and foraminifera, but aptychi (ammonite opercula) were present. Modern half-spreading rates along mid-ocean rifts, as revealed by magnetic reversal anomalies, appear to result in the generation of 2.5 km2 per yr of new ocean crust (Deffeyes, 1970). This is sufficient to repave the deep ocean floor in 120 X 106 yr. This, of course, does not mean that all of the ocean floor is post mid- Mesozoic. Regions of low spreading rate, such as in the North At- lantic, or those protected from subduction may be considerably older. For example, the Antarctica plate is, in a sense, a "non- plate" in that it has no subduction zone at least at present. It fol- lows that any portion of the Antarctica plate adjacent to Antarc- tica, where the continental slope was not initially borne by a ridge or transform fault, might be a sector of stranded Paleozoic crust. This was the rationale of Dietz and Holden (1971) in identifying the Wharton Basin as possibly being underlain by Paleozoic crust. However, DSDP results almost certainly demonstrate that this crust is young; that is, not older than mid-Mesozoic. Other potential regions of old crust, possibly protected from de- struction by subduction, have encountered a similar fate — for ex- ample, the Caribbean and behind-the-arc basins such as the Philip- pine Sea basin. DSDP planners have been continuously interested in drilling into Paleozoic sediments but have found potential sites difficult to identify (William Hay, 1973, oral commun.). The exten- sive seismic reflection surveys which now have been made around the world reveal, with few exceptions, only a thin cover of pelagics (that is, acoustically transparent sediments) of usually < 500 m. The last sanctuary for an extensive Paleozoic layer is within Layer 3, on the assumption that this Oceanic Layer may not be gabbro and closely related rocks but may be metamorphosed Paleozoic and Precambrian sediments. Although an unlikely view, seismic refraction data do not entirely eliminate this possibility. The proposed International Program of Ocean Drilling, a follow- up to DSDP, would direct much attention to the nature of Layer 3. It is abundantly evident, however, that deep ocean drilling to date has provided strong confirmation of plate tectonics. REFERENCES CITED Brown, Bahngrell W., 1974, Sediment accumulation, sea-floor spreading, and eustacy: Discussion: Geol. Soc. America Bull., v. 85, p. 831. Chamberlin, T. C, 1909, Diastrophism as the ultimate basis of correlation: Jour. Geology, v. 17, p. 685-693. Deffeyes, K. S., 1970, The axial valley: A steady-state feature of the terrain, in Johnson, H., and Smith, B., eds., Megatectonics of connnents and ocean basins: Rutgers Univ. Press, p. 194-222. Dietz, R. S., and Holden, J. C, 1971, Pre-Mesozoic oceanic crust in the eastern Indian Ocean (Wharton Basin): Nature, v. 229, no. 5283, p. 309-312. Rona, Peter A., 1973a, Relations between rates of sediment accumulation on continental shelves, sea-floor spreading, and eustacy inferred from the central North Atlantic: Geol. Soc. America Bull., v. 84, p. 2851-2872. 1973b, World-wide unconformities in marine sediments related to eustatic changes of sea level: Nature Physical Science, v. 244, p. 25-26. Rona, Peter A., and Wise, D. U., 1974, Global sea level and plate tectonics through time: Geol. Soc. America, Geology, v. 2, no. 3, p. 133-134. Sloss, L. L., 1963, Sequences in the cratonic interior of North America: Geol. Soc. America Bull., v. 74, p. 93-1 14. 1973, Tectonic and eustatic (?) factors in late Precambrian-Phanerozoic global sea-level changes: Geol. Soc. America, Abs. with Programs (Ann. Mtg.), v. 5, no. 7, p. 813-814. Spieker, E. M., 1946, Late Mesozoic and early Cenozoic history of central Utah: U.S. Geol. Survey Prof. Paper 205-D, p. 117-161. 1949, Sedimentary facies and associated diastrophism in the upper Cretaceous of central and eastern Utah: Geol. Soc. America Mem. 39, p. 55-82. Suess, E., 1906, The face of the earth: Oxford, Clarendon Press, v. 2, 556 p. Marine Geology, 16(1974) 275—292 ©Elsevier Scientific Publishing Company, Amsterdam — Printed in The Netherlands ABYSSAL HILLS OF THE EASTERN CENTRAL NORTH ATLANTIC PETER A. RONA, REGINALD N. HARBISON and SAM A. BUSH Atlantic Oceanographic and Meteorological Laboratories, National Oceanic and Atmospheric Administration, Miami, Fla. (U.S.A.) (Accepted for publication January 25, 1974) ABSTRACT Rona, P. A., Harbison, R. N. and Bush, S. A., 1974. Abyssal hills of the eastern central North Atlantic. Mar. Geol., 16: 275—292. Abyssal hills were delineated in a 185 X 185-km area by an 18.5 X 18.5-km grid of narrow-beam bathymetric and geophysical profiles in oceanic crust of Cretaceous age near 23°N latitude, 31°W longitude. The abyssal hills are similar to features located along flow lines of sea-floor spreading near the crest of the Mid-Atlantic Ridge. This similarity indicates a primary origin for these abyssal hills related to axial processes at a mid-oceanic ridge involving construction (igneous) and tectonics (faulting), and secondary modification by volcanic activity. INTRODUCTION The area of abyssal hills selected for investigation in the central North Atlantic lies within the corridor of the Trans-Atlantic Geotraverse (TAG) of the National Oceanic and Atmospheric Administration (Rona, 1973) which provides a framework for study of the structural evolution of oceanic crust from the Mid-Atlantic Ridge to the continental margins (Fig.l). The area investigated includes the transition zone between the abyssal hills and the abyssal plain physiographic provinces where sediments of the abyssal plain interfinger with the abyssal hills. Heezen et al. (1959, pp.61— 63) define an abyssal hill as "a small hill that, rises from the ocean basin floor and is from a few meters to a few hundred meters in height and from about one hundred meters to a few kilometers in width". The province of abyssal hills covers about 85% of the Pacific basin (Menard, 1964, p.35), about 50% of the Atlantic basin (Heezen et al., 1959; Heezen and Holcombe, 1965) and probably a significant percent of the Indian Ocean making it the largest of all physiographic provinces, in the North Atlantic the abyssal hills province is distributed along the basins which parallel the eastern and western flanks of the Mid-Atlantic Ridge and merge into the topography of the crestal region. 1074 276 50°W 45°W 40°W 35°W 30°W 20°W 15°W 1 lJ=i^a»J-30oN CANARY ISLANDS 25°N 20°N Fig.l. Physiographic diagram of the eastern central North Atlantic (Heezen and Tharp, 1968) outlining study areas of the abyssal hills (this paper) and the Mid-Atlantic Ridge crest (Ronaetal., 1973, 1974) within the corridor of the Trans-AtlanticGeotraverse( dashed lines). Sites 137 and 138 of the Deep Sea Drilling Project are shown (Hayes et al., 1972). The present study is addressed to four basic questions regarding the abyssal hills investigated: (1) How are the hills primarily formed? Are the hills formed by tectonic (faulting) or constructional (igneous) processes, or by a combination of the two? (2) Where are the hills primarily formed? Are the hills formed at or away from the axis of a mid-oceanic ridge? (3) How do secondary processes act to modify the primary structure of the hills? (4) Where do secondary processes act to modify the primary structure? It is unlikely that the answers to these questions are the same for all abyssal hills. PREVIOUS WORK In addition to their physiographic affinity, seismic reflection and refraction measurements indicate that abyssal hills are part of the second layer of oceanic crust. Because layer 2 is assumed to be composed primarily of basalt generated by sea-floor spreading, previous studies have attempted to relate the structure of abyssal hills to axial processes of mid-oceanic ridges. Menard and Mammerickx (1967) recognized that the trend of abyssal hills and magnetic anomalies generally parallels the axes of mid-oceanic ridges. They studied the area situated between the crest and a distance corresponding to a crustal age of about 40 m.y. of the East Pacific Rise, the Gorda Ridge, and the Juan de Fuca Ridge. They inferred that, "The hills may be produced either by the accumulation of lava flows around opening rifts or by the rifting of such flows or by a combination of the two." A survey of a 230-km2 area of abyssal hills on the central equatorial Pacific 1075 277 (Moore and Heath, 1967) revealed elongate abyssal hills trending north- south with 50- to 200-m relief covered by sediment ranging in thickness from 100 m over crests up to 440 m in depressions. Abyssal hills in a 165 X 450-km area just south of the Aleutian Trench (Naugler and Rea, 1970) are elongate and range up to about 300 km in length. The hills are spaced between 10 and 40 km apart, and are parallel to linear magnetic anomalies 60—75 m.y. in age, spaced 20—60 km apart. In their investigation of the Mid-Atlantic Ridge between 6 and 8° S latitude Van Andel and Heath (1970) noted a discrepancy between rela- tively close fault spacing and non-linear topography of the crestal region and wider fault spacing and linear topography parallel to the ridge axis beginning about 100 km east of the ridge crest. They attribute these differ- ences to a discontinuity in axial processes. Luyendyk (1970) used near- bottom towed geophysical instrumentation to delineate two abyssal hills in the northeast Pacific (vicinity 32°25'N, 125°45'W). He ascribed a compound origin for a shield-shaped hill involving primary construction (accumulation of lava flows and volcanic knobs at the crest of a spreading ridge) modified by secondary faulting away from the ridge crest. He ascribed a secondary tectonic origin (faulting at a distance from the ridge crest along an inherited two-dimensional structural grain of weakness) for a block-shaped abyssal hill. Larson (1971) used similar instrumentation to delineate abyssal hills about 5 km wide by 200 m high elongated parallel to the axis of the East Pacific Rise (near 21°N, 109° W); he ascribed a compound origin to these abyssal hills involving primary faulting in a 5 km wide zone of crustal extension and volcanism within a 100 m wide center of intrusion at the ridge crest. Andrews (1971) interpreted a single asymmetrical abyssal hill elongated oblique to a branch of the Mendocino Fracture Zone in the northeast Pacific (36° N, 157°W) as due to secondary faulting and associated volcanism at a distance from the East Pacific Rise corresponding to a crustal age of 36—47 m.y. Four elongate, sediment-covered abyssal hills delineated in the equatorial Pacific (14°N, 126°W) by near -bottom towed geophysical instruments are oriented approximately perpendicular to major fracture zones and parallel to remanent magnetic anomalies indicating a crustal age of 32 ± 5 m.y. (Mudie et al., 1972). MEASUREMENTS The 185 X 185-km (34 X 103 km2 ) study area (Fig.l) was investigated with an 18.5 X 18.5-km grid of geophysical profiles (Fig. 2). Measurements included narrow-beam bathymetry (theoretical total beamwidth about 6° ; effective total beamwidth about 20° ), gravity, magnetics, continuous seismic reflection (655 cm3 (= 40 in.3 ) air gun), and wide-angle reflection (sonobuoys). Primary position control was by satellite navigation. 1076 278 Fig. 2. Tracklines of concurrent narrow-beam bathymetric, gravimetric, magnetic and seismic reflection (along thick lines only) profiles, and a wide-angle reflection station (4). BATHYMETRY Two bathymetric trends predominate within the study area (Figs. 3— 5): (1) elongate ridges and intervening valleys trending northeast— southwest cover about 70% of the area, (2) two linear valleys trend northwest— south- east transverse to the elongate ridges and valleys and cover about 20% of the area. Topography is subdued in the remaining 10% of the area that is transitio- nal between the abyssal hills and the abyssal plain. The elongate ridges and valleys trend 047 ± 5° except in the northwest corner of the area where the trend changes to 010 ± 5°. The distance between the sub-parallel ridge crests varies between 5 and 20 km with an 1077 279 Fig. 3. Bathymetric map of the abyssal hills study area. Isobaths are in hundreds of meters at a 200-m interval and are corrected for vertical sounding velocity according to Matthews (1939). The shaded area is underlain by sediments with the characteristics of turbidites on seismic reflection profiles; the remaining areas are underlain by a variable thickness of pelagic sediments. average separation of 13 km. The average relief from valley-to-ridge crest is 600 m ranging between depths of 4800 and 6200 m. A narrow-beam bathymetric profile shows features characteristic of cross sections of the ridges (Fig. 6). About 90% of the echo returns from the ridges are hyperbolic crescents generated as diffractions from peaks and edges indicating that the ridge surfaces are extremely rough relative to the 12.5-cm wave-length of the projected acoustic pulse. The ridges exhibit two major topographic elements: a base hundreds of meters high surmounted by a superstructure of irregular peaks tens to hundreds of meters high. The slopes of the bases measured at 60 of the abyssal hills along profiles 1—11 (Figs. 2, A) 1078 280 NW ° VERTICAL EXAGGERATION 251 Fig. 4. Bathymetric, free-air gravity anomaly (dashed curves) and residual magnetic profiles (solid curves) 1—11 (Fig.2). 1079 281 SW 0 KM VERTICAL EXAGGERATION 25 I Fig. 5. Bathymetric, free-air gravity anomaly (dashed curves) and residual magnetic profiles (solid curves) 12—22 (Fig.2). 1080 Fig. 6. Narrow-beam bathymetric profile typical of transverse crossings of the elongate ridges. The markings on the profile are field annotations and points at which depth was digitized. range between about 5 and 35° with the greatest number between 10 and 15° . About one-third of the bases are symmetrical and two-thirds are asymmetrical. Bases with slopes greater than 20° tend to be asymmetrical. The slope is steeper on the northwest than the southeast side of about two- thirds of those bases that are asymmetrical. The peaks surmounting the bases appear similar to volcanic knobs resolved by deep-towed instrument surveys of Pacific abyssal hills (Luyendyk, 1970). In contrast to the ridges, the bathymetric profiles across the intervening valleys exhibit predominantly specular (mirror) reflection returns evidenc- ing a relatively smooth surface. The valley floors are generally concave-up between adjacent ridges and abut the bases of the ridges at obtuse angles. The two linear tranverse valleys each trend 112° respectively across the center and along the southern margin of the study area (Fig. 3). The axes of the valleys are about 75 km apart and the width of each valley is about 10 km. The topographic relations between these linear transverse valleys and 1081 283 the elongate ridges and valleys are complex. The angle of intersection between the two sets of features is 65 ± 5° . The northern margins and a portion of the southern margins of both linear transverse valleys merge with the adjacent elongate valleys. A ridge about 10 km wide which attains about 1200 m relief extends for a distance of about 110 km along the southern margin of the central linear transverse valley. Indications exist that a similar ridge may extend along the corresponding portion of the second linear transverse valley beyond the southern edge of the study area. GRAVITY The free-air gravity anomaly map of the study area (Fig. 7) exhibits a range of values between —10 and +20 milligals with anomaly axes distributed along the two predominant bathymetric trends. The gravity agrees in magnitude with a rough calculation of the terrain effect (0.07 milligal per meter relief). These observations indicate that most of the free-air anomalies are due to topography and no marked lateral density variations are present within the accuracy (several milligals) and resolution of the measurements. MAGNETICS Magnetic anomalies within the study area range from —150 to +200 gammas and exhibit two predominant trends which generally parallel the two principal bathymetric trends (Figs. 3, 8). The peak-to-peak wavelength of the anomalies ranges between about 10 and 40 km (Fig. 4), twice the range of the crest-to-crest distance between the elongate ridges. Correlation of magnetic anomalies is difficult in this region of the Atlantic owing in part to the highly fractured character of the oceanic crust. The northeast— southwest trend of magnetic anomalies in the study area is consistent with that determined locally (Lattimore et al., 1974, fig.l) and regionally (Pitman and Talwani, 1972, fig.2). Lattimore et al., (1974) determined that the anomaly designated K-6 of Late Cretaceous age in the geomagnetic polarity time scale of Vogt and Johnson (1971) extends through the central portion of the study area. SEISMIC REFLECTION PROFILES Seismic reflection profiles were made across sites 137 and 138 of the Deep Sea Drilling Project located about 450 km northeast of our study area (Fig.l). The stratigraphic sections determined by drilling at those two sites (Hayes et al., 1972) were used to identify the lithology and ages of intervals on the seismic reflection profiles (Fig.9). The sediment columns at sites 137 and 138 extend from Late Cretaceous to Late Tertiary and overlie undated basalts of the acoustic basement. At both sites the Late Cretaceous sediment is fine-grained and forms an acoustically transparent layer that conforms with the irregular surface of the underlying basalt in a manner 1082 284 Fig.7. Free-air gravity anomaly map (milligals) of the abyssal hills study area. characteristic of pelagic deposition. The overlying Tertiary sediments differ at the two sites. Pelagic deposition continues to conform with the topo- graphy at site 137. At site 138 an interval containing planar reflection interfaces sub-parallel with the sediment — water interface fills the topo- graphic lows in a manner characteristic of turbidite deposition. The turbidite depositional process involves density currents of sediment— water mixtures that flow downslope and deposit nearly horizontal layers. It follows that the planar reflection interfaces, probably corresponding to extensive graded layers of relatively coarse-grained sediment, constitute structural datums to detect post -depositional differential vertical crustal movements. Alternatively, the pelagic depositional process involving particle- by-particle deposition from volume suspension in the water column con- 1083 285 Fig. 8. Magnetic anomaly map (gammas) of the abyssal hills study area. The regional magnetic field has been removed according to IAGA (1969). forms to the original depositional surface and sediments deposited by this process cannot be used as structural datums. The two "type" seismic profiles across sites 137 and 138 (Fig.9) were compared with seismic reflection profiles of the study area. About 75% of the study area is covered with an irregular, discontinuous layer of pelagic sediment ranging up to about 255 m (0.3 sec; based on 1.7 km sec-1 seismic velocity determined by reflection travel time through interval drilled at site 137) in thickness (Fig. 3). Where the pelagic layer is relatively thick, as in profile 17A of Fig. 10 (170 m — 0.2 sec), the seismic profile resembles the profile across site 137 (Fig.9) suggesting that a nearly corresponding Late Cretaceous through Tertiary sedimentary sequence is present overlying acoustic basement of basalt. The irregular, discontinuous nature of the 1084 SITE 137 w 0 KILOMETERS AGE 7.50 spNL JUta EARLY CAMPANIAN 2 TO MAESTRICHTIAN LATE CENOMANIAN TO EARLY TURONIAN LATE ALBIAN TO LATE CENOMANIAN BASALT 7.00 >- < 6 5 7.50 SITE 138 w 0 KILOMETERS 5 AGE EARLY EOCENE TO MIOCENE CAMPANIAN TO OANIAN hgmm 4 CENOMANIAN Si BASALT Fig. 9. Our seismic reflection profiles across Deep Sea Drilling sites 137 and 138. Intervals between reflecting interfaces are identified according to Hayes et al. (1972). Numbered intervals correspond to lithologic units described in Hayes et al. (1972). 1085 287 UJ g O _ UJ o uf "J UJ a: < o rEN "7* — : : -8 V 9- 22A, Fig. 10. Seismic reflection profiles which cross the two linear transverse valleys. The !abeled profiles are located on Fig. 2. pelagic layer may be partially attributed to the activity of gravitational mass movements of the sediment, an interpretation supported by the observation that the pelagic sediment tends to be thickest in topographic lows. Thick- ening of pelagic sediment in topographic lows and normal faulting of sediment on topographic highs was noted in studies of Pacific abyssal hills and also attributed to gravitational mass movements (Moore and Heath, 1967; Mudieetal., 1972). About 25% of the study area is covered by sediments displaying the characteristics of turbidities on the seismic profiles (Fig. 3). The intervals containing planar reflection interfaces characteristic of turbidites (Fig. 10, 1086 288 profiles 21A and 22A; Fig. 11) attain thicknesses up to 300 m (0.33 sec) based on a compressional velocity of 1.8 km/sec measured by wide-angle reflection at site 138 and at profile 22 A (Figs.2, 10, 11). The turbidites are underlain by an interval of acoustically transparent material up to about 215 m (0.25 sec) thick. The similarity of the profiles cited in the study area with the type profile at site 138 (Fig. 9) suggests that the turbidites in the study area are Tertiary in age and overlie Late Cretaceous pelagic sediments. In map view the turbidites occupy valleys below the 5600-m isobath in the northern half of the study area (Fig. 3). Turbidites also occupy portions of the central linear transverse valley. In cross section the turbidites thin in a westward direction as shown on Fig.ll, profile 2 A, where the turbidites thin from about 400 m (0.45 sec) to about 90 m (0.10 sec) in a distance of 60 km. The turbidites also thin from northeast to southwest as shown in Fig.ll, profile 21C, where the section thins from about 450 m (0.50 sec) to about 225 m (0.25 sec) in a distance of about 80 km. On both seismic profiles 2A and 21C, the turbidites occupy valleys between elongate ridges (Figs.2, 3, 11). The depth below sea level to buried acoustic basement beneath each of the valleys is constant while the sediment-^water interface steps down in the direction of sediment thinning. This observation indicates that the different levels of turbidites in the various valleys results from deposition as distin- guished from differential vertical movements of the underlying basement. The inference that differential vertical movement has been negligible is supported by the nearly horizontal attitude of the turbidite layers with the exception of upward-concavity at the center of valleys, explicable by differential vertical compaction proportional to the thickness of the sediment column. The expected flow direction of turbidity currents into the study area is from east to west down the adjacent continental slope and rise of north- west Africa (Fig.l). However, various lines of evidence indicate a north-to- south component in the flow direction: (1) Turbidites fill the northeast— southwest trending elongate valleys of the northern half of the study area. (2) Turbidites are absent in the southern half of the study area. (3) Turbidites thin from northeast to southwest (Fig.ll, profile 21C). (4) Turbidites are present at the eastern and western ends of the central linear transverse valley (Fig. 10, profiles 21 A, 22 A and 13A) and absent in the middle of the valley (Fig. 10, profile 17A between profiles 21A and 13A). If the turbidity currents flowed from east-to-west, the central linear transverse valley which has a continuous westward gradient would be filled with turbidites. Apparently, the turbidites entered that valley only where continuous connections exist with the northeast— southwest trending valleys to the north. (5) The adjacent abyssal plain extends from northeast to southwest and terminates at the latitude of the study area (Fig.l). 1087 289 P*^f' # Si o CVJ <% .;v*i <^C t* E30-^S*" — h c ° o o > x j. *■< ~" o> 0) a J3 a *• 3 .5 "-1 s^ - O F "S tH 01 «| 3 0£ « i 92 o> *> -Q — 3 «1 O H — .2 «' 1 < >> 0 N 13 » S o > "O o -10 c .-s ft OT CC 03 ^ <«-l l- dges turbi ion o Ul s o *•* ^ rt -J *» > St U) 01 cfl « — X 0 ■£ * i-c « y ■— -w .3 j- h -Cm® £ Ji> _ -*J w w .8 a & *** is — a E > : - c — 5 O C s scti pro ene c x -° o> o *; s- nj C ■'„ mic on e erne U5 W r » rt 01 r- XI — u p-i "ti '-£ UD W 0 6h -o 1088 290 DISCUSSION What can be inferred from the evidence presented to differentiate between primary and secondary origin of the various features described and to deter- mine the tectonic and constructional processes in their development? The correspondence between the Late Albian to Cenomanian age of pelagic sediment inferred from Deep Sea Drilling Project sites 137 and 138 (Figs. 9, 10) and the Late Cretaceous age of the underlying basalt inferred from the identification of remanent magnetic anomalies in the geomagnetic polarity time scale confirms that the basaltic crust underlying the abyssal hills in the study area was generated by sea-floor spreading about the Mid-Atlantic Ridge in the early Late Cretaceous. This information does not provide evidence of the structures that were present in the basaltic crust at that time because the pelagic sediment would have conformed to the original surface and would have adjusted to subsequent deformation. The presence of turbidites, inferred to be of Tertiary age by similarity of seismic reflection character with Tertiary turbidites at Deep Sea Drilling Project site 138 (Fig. 9), in the elongate valleys of the northern half of the study area and in portions of the central linear transverse valley indicates that both types of valleys must have existed at least since early Tertiary times. The lack of marked deformation of the turbidite layers and the constant level of the acoustic basement beneath valleys indicate that local differential vertical movements, as distinguished from regional subsidence, have been negligible at least since early Tertiary. The depth and inferred age of basaltic basement in the study area are consistent with the distribu- tion of oceanic depth as a function of age (Menard, 1969; Sclater et al., 1971) and of lithospheric plate geometry (Rona, 1971). It is necessary to introduce evidence from outside the study area in order to consider the existence of the elongate ridges and valleys and the linear transverse valleys in the time interval between crustal generation in the early Late Cretaceous and the Tertiary. In 1972 the NOAA ship "Discoverer" performed a survey of an area of the Mid- Atlantic Ridge (Rona et al., 1973) located along flow lines of sea-floor spreading from the ridge to the study area of the abyssal hills (Fig.l; Pitman and Talwani, 1972, fig.2). Two predominant bathymetric trends were delineated on the Mid- Atlantic Ridge comparable to those in the abyssal hills region: (1) elongate ridges and valleys, (2) linear transverse valleys. The elongate ridges and valleys delineated on the Mid-Atlantic Ridge are of comparable dimensions in map view but of greater relief than those of the abyssal hills study area (Rona et al., 1973). The elongate ridges and valleys tend to be sub-parallel to the adjacent rift valley of the ridge (azimuth 025°). The linear transverse valleys of the Mid-Atlantic Ridge are roughly 10 km wide and are spaced between 40 and 60 km apart. The valleys extend up to the rift valley which they join at an angle of about 90° (azimuth 115°) on the eastern side and about 60° (azimuth 265°) on the western side of the ridge. Small right lateral deviations up to 10 km in Margo 529: First Proofs. Page 16. 1089 291 the trend of the median valley occur at the junctures with the linear trans- verse valleys. The linear transverse valleys are interpreted as fractures formed by thermal contraction of the sea floor adjacent to the rift valley of a slow- spreading mid-oceanic ridge (Rona et al., 1974). The similarity of topography between the crestal region of the Mid- Atlantic Ridge and the abyssal hills, in particular the elongate ridges and valleys and the transverse valleys, indicates that the abyssal hills are primary features which originated about a spreading mid-oceanic ridge. It is inferred from the slopes of the bases of the elongate ridges that both con- structional and tectonic processes have interacted in their development. The lower range of inclinations (5—20° ) comprising 85% of the measurements are consistent with construction by basalt which has too low a viscosity to sustain much higher slopes (MacDonald, 1963), although low-angle faulting cannot be precluded. The remaining 15% of the measurements comprising the higher range of inclinations (25—35° ) are more likely attributed to faulting. Volcanic activity such as that which has occurred at various times during the Cenozoic in the central North Atlantic, as evidenced by Oligocene (38—30 m.y. B.P.) igneous rocks underlying Bermuda (Reynolds and Aumento, 1973) and recent eruptions on the Canary and Cape Verde islands (Fig.l), may have secondarily modified the superstructure of the abyssal hills. ACKNOWLEDGEMENTS We thank Captain Robert C. Munson, the officers and crew of the NOAA ship "Discoverer" for their willing cooperation. Discussions with Leroy M. Dorman of NOAA regarding gravity were helpful. We thank George H. Keller and B. A. McGregor of NOAA and Mark L. Holmes of the University of Washington for helpful reviews. This study was performed as part of the Trans-Atlantic Geotraverse (TAG) of the National Oceanic and Atmospheric Administration (NOAA). REFERENCES Andrews, J. E., 1971. Abyssal hills as evidence of trans-current faulting on North Pacific fracture zones. Geol. Soc. Am. Bull., 82: 463-470. Hayes, D. E., Pimm, A. C, Beckmann, J. P., Benson, W. E., Berger, W. H., Roth, P. H., Supko, P. R. and Von Rad, U., 1972. Initial Reports of the Deep Sea Drilling Project, 14. U.S. Government Printing Office, Washington, D.C., 975 pp. Heezen, B. C. and Holcombe, T. L., 1965. Geographic distribution of bottom roughness in the North Atlantic. Lamont Geological Observatory, Columbia University, Palisades, New York, N.Y., 41 pp. Heezen, B. C. and Tharp, M., 1968. Physiographic diagram of the North Atlantic Ocean. Geol. Soc. Am. Spec. Paper 65, pp.1— 122 (revised). Heezen, B. C, Tharp, M. and Ewing, M., 1959. The floors of the Oceans, 1. The North Atlantic. Geol. Soc. Am. Spec. Paper 65, 122 pp. IAGA Commission 2, Working Group 4, 1969. International geomagnetic reference field 1965. J. Geophys. Res., 74: 4407-4408. 1090 292 Larson, R. L., 1971. Near-bottom geologic studies of the East Pacific Rise crest. Geol. Soc. Am. Bull., 82: 823—842. Lattimore, R. K., Rona, P. A. and Dewald, O. E., 1974. Magnetic anomaly sequence in the Central North Atlantic. J. Geophys. Res., 79: 1207—1209. Lister, C. R. B., 1971. Crustal magnetiziation and sedimentation near two small sea- mounts west of the Juan de Fuca Ridge, northeast Pacific. J. Geophys. Res., 76: 4824—4841. Luyendyk, B. P., 1970. Origin and history of abyssal hills in the northeast Pacific Ocean. Geol. Soc. Am. Bull., 81: 2237—2260. MacDonald, G. A., 1963. Physical properties of erupting Hawaiian magmas. Geol. Soc. Am. Bull., 74: 1071-1078. Matthews, D. J., 1939. Tables of the velocity of sound in pure water and sea water. Hydrographic Department, Admiralty, London, 52 pp. Menard, H. W., 1964. Marine Geology of the Pacific. McGraw-Hill, New York, N.Y., 271 pp. Menard, H. W., 1969. Elevation and subsidence of oceanic crust: Earth Planet. Sci. Lett., 6: 275-284. Menard, H. W. and Mammerickx, J., 1967. Abyssal hills, magnetic anomalies and the East Pacific. Earth Planet. Sci. Lett., 2: 465—472. Moore, T. C. and Heath, G. R., 1967. Abyssal hills in the central equatorial Pacific: detailed structure of the sea floor and subbottom reflectors. Mar. Geol., 5: 161—179. Mudie, J. D., Grow, J. A. and Bessey, J. S., 1972. A near-bottom survey of lineated abyssal hills in the equatorial Pacific. Mar. Geophys. Res., 1: 397 — 411. Naugler, F. P. and Rea, D. K., 1970. Abyssal hills and sea-floor spreading in the central North Pacific. Geol. Soc. Am. Bull., 81: 3123—3128. Pitman, III, W. C. and Talwani, M., 1972. Sea-floor spreading in the North Atlantic. Geol. Soc. Am. Bull., 83: .619—646. Reynolds, P. H. and Aumento, F., 1973. Deep Drill — 1972: geochronology of the Bermuda drill core. EOS, Am. Geophys. Union Trans., 54(4): 485. Rona, P. A., 1971. Depth distribution in ocean basins and plate tectonics. Nature, 231: 179—180. Rona, P. A., 1973. Marine geology. In: McGraw-Hill Yearbook of Science and Technology, McGraw-Hill, New York, pp.252— 256. Rona, P. A., Harbison, R. N., Bassinger, B. G., Butler, L. W. and Scott, R. B., 1973. Asymmetrical bathymetry of the Mid-Atlantic Ridge at 26° N latitude. EOS, Am. Geophys. Union Trans., 54(4): 243. Rona, P. A., Harbison, R. N. Bassinger, B. G., McGregor, B. A. and Scott, R. B., 1974. Fracture valleys of the Mid- Atlantic Ridge (26° N latitude). Geol. Soc. Am. Bull, (in press). Sclater, J. G., Anderson, R. N. and Bell, M. L., 1971. Elevation of ridges and evolution of the central eastern Pacific. J. Geophys. Res., 76: 7888—7915. Van Andel, T. H. and Heath, G. R., 1970. Tectonics of the Mid-Atlantic Ridge, 6—8° south latitude. Mar. Geophys. Res., 1: 5—36. Vogt, P. R. and Johnson, G. L., 1971. Cretaceous sea-floor spreading in the western North Atlantic. Nature, 234: 22—25. 1091 Symposium: Global Sea Level and Plate Tectonics through Time Peter A. Rona, Atlantic Oceanographic and Meteorological Laboratories, National Oceanic and Atmospheric Administration, Miami, Florida 33149 and Donald U. Wise, Department of Geology, University of Massachusetts, Amherst, Massachusetts 01002 The ideas expressed in the symposium "Global Sea Level and Plate Tectonics through Time" are part of the evolution of thought on eustatic theory (Fairbridge, 1961 ). Many of our predecessors, including Darwin, Chambers, Suess, Grabau, Sti lie, Bucher, Umbgrove, and Kuenen, recognized that tectono- eustatic processes affecting the cubic capacity of the ocean basins are capable of primary control of eustatic sea-level changes at times other than ice ages. Their ideas were based on limited knowledge of ocean basins and various global tectonic theories that have been largely debunked. An enhanced under- standing of global sea level is emerging from the increase in our knowledge of the ocean basins and the development of the theory of plate tectonics. Laurence L. Sloss, Northwestern University, emphasized the need for caution in discriminating between the effects of cratonal tectonics and of eustatics. The cratons are active and form their own imprint on the total sediment regime manifested in the recognized Sloss cratonic stratigraphic sequences ( 1 963, 1973a, 1973b). A. Hallam, Oxford University, along with H. W. Menard (1964), was among the earliest to recognize the quantitative importance of reversible changes in the volume of mid-oceanic ridges in the control of global sea level. Using biostratigraphic correlation techniques, Hallam demonstrated the synchroneity of oscillations with periodicities of 10s to 106and 107tol08yr superposed on continental epeirogenic movements during Jurassic time. He attributed an apparent emergence of continents over the past approximately 109 yr based on the Egyed curve (1956) primarily to the process of "continental underplating" (Hallam, 1963, 1969, 1971, 1973). Erie G. Kauffman, U.S. National Museum, developed an integrated biostratigraphic geochronologic system for Cre- taceous time which provides evidence for a sequence of synchro- nous world-wide transgressions and regressions on a time scale of 10 to 107 yr. The transgressive-regressive sequence on island arcs is the reverse of the sequence on cratonii; interiors and margins (1972, 1973a, 1973b). Walter C. Pitman III and James D. Hays, Lamont-Doherty Geological Observatory, Columbia University, demonstrated quantitatively that the world-wide middle-to-Late Cretaceous transgression and subsequent regression may have been caused by a contemporaneous pulse of rapid sea-floor spreading at most of the mid-oceanic ridges between 100 to 85 m.y. The rapid spreading caused the ridges to expand and hence reduced the volumetric capacity of the ocean basins, resulting in as much as 500 m of vertical sea-level change. Cenozoic continental emergence has resulted from a reduction in sea-floor spreading rates (Larson and Pitman, 1972; Hays and Pitman, 1973; Pitman and Hays, 1973). Nicholas C. Flemming and David G. Roberts, National Institute of Oceanography, United Kingdom, constructed theoretical hypsographic curves corresponding to various dis- tributions of mass between continents and ocean basins. They emphasized the complex interaction between factors affecting the form of the Earth's crust and the total volume of ocean water in determining the magnitude and rate of eustatic move- ments (1973a, 1973b). Peter A. Rona interpreted rates of sediment accumulation on subsiding continental margins and in ocean basins as indices of the state of the global plate tectonics system. The rates of sediment accumulation over a time scale of 106 to 1 07 yr are related through cyclic eustatic sea-level fluctuations to rates of sea-floor spreading, reversible volume changes of the mid- oceanic ridge system, and net orogenic state of the continents (1973a, 1973b, 1973c). Donald U. Wise proposed a constant freeboard model in which the relative elevation of continents with respect to sea level is a function of the rate of operation of the plate tectonics system. The Wise freeboard model reflects a precontinental break-up rate during Paleozoic time and a postcontinental break-up rate during Mesozoic and Cenozoic times, as opposed to Egyed's (1956) interpretation of progressive continental emergence throughout Phanerozoic time (Wise, 1972, 1 973). Eustatic changes of sea level manifest volume-area-isostasy relations between continents and ocean basins that are recorded in the curve of continental freeboard. The symposium papers presented evidence defining portions of the freeboard curve and controversial speculation regarding the controlling processes. Definition and interpretation of the continental freeboard curve through time present a unifying challenge to geoscientists. REFERENCES CITED Egyed, L., 19S6, Determination of changes in the dimensions of the earth from paleogeographical data: Nature, v. 178, p. 5 34. Fairbridge, R. W., 1961 , Eustatic changes in sea level. Vol. 4, in Ahrens. L. H., Press, F., Rankama, K.. and Runcorn, S. K., eds., Physics and chemistry of the Earth: London, Pergamon Press, p. 99-1 85. Flemming, N. C, and Roberts, D. G., 1973a, Tectono-eustatic changes in sea level and sea floor spreading: Nature, v. 243, p. 19-22. 1973b, Eustatic changes in sea level during the Mesozoic and Cenozoic, causes and effects: Geol. Soc. America, Abs. with Programs (Ann. Mtg.), v. 5, no. 7, p. 622. Hallam A., 1963, Major epeirogenic and eustatic changes since the Cretaceous and their possible relationship to crustal structure: Am. Jour. Sci., v. 261 , p. 397-423. 1969, Tectonism and eustacy in the Jurassic: Earth-Sci. Rev., v. 5(1), p. 45-68. 1971, Mesozoic geology and the opening of the North Atlantic: Jour. Geology, v. 79, p. 129-157. 1973, Heirarchical pattern of Phanerozoic eustatic changes: Geol. Soc. America, Abs. with Programs (Ann. Mtg.), v. 5, no. 7, p. 650-651. Hays, James D., and Pitman, Walter C, III, 1973, Lithospheric plate motion, sea level changes and climatic and ecological con- sequences: Nature, v. 246, p. 18-22. Kauffman, Erie G., 1972, Evolutionary rates and patterns of North American Cretaceous mollusca: Internal. Geol. Cong., 24th, Montreal 1972, sec. 7, p. 174-189. 1973a, Cretaceous bivalvia, in Hallam, A., ed.. Atlas of palaeo- biogeography: Amsterdam, Elsevier, p. 353-383. 1973b, Stratigraphic evidence for Cretaceous eustatic changes: Geol. Soc. America, Abs. with Programs (Ann. Mtg.), v. 5, no. 7, p. 686-687. Larson, R. L., and Pitman, W. C, III, 1972, World-wide correlation of Mesozoic magnetic anomalies and its implications: Geol. Soc. GEOLOGY 2, No. 3, 133-4, 1974. 133 1092 An'.'rica K :!'... v .'■'. r. .' '■'■-'• -il. Geol. Soc. America, Abs. with Programs (Ann. Mtg.), v. 5, Menard. :l. '.'. ....... "... . .;. of the Pacific: New York, McGraw- no. 7, p. 78 S. 1 1 1 i I liook L.i.. 271 p. Sloss, L. L., 1963. Sequences in I lie era tonic interior of North America: l'i! nun. Walter L'.. II!. in 1 ! ! . -. Janes !).. 197 3, Upper Cretaceous Geol. Soc. America Hull., v. 7 J. p. 9 3-1 14. spreading rates ■. :-.J i;.. -. a: tr.iii^-ression: Geol. Soc. America. 1973a. Mode and history of vertical deformation of continental Abs. with I'rojrj;::* (Ann. ' it ;.l. \ . S. no. 7, p. 768. interiors: EOS (Am. Geophys. Union Trans.), v. 5 4(4), p. 454. Rona. Peter A.. 1 9 7 3a, Relations be: ween race:, of sediment accumulation 1973b. Tectonic and eustatic(?) factors in late Precambnan- on continental shelves, sea floor spreading, and eustacy inferred Phanerozoic global sea-level changes: Geol. Soc. America, Abs. from the central North Atlantic: Geol. Soc. America Bull., with Programs (Ann. Mtg.), v. 5, no. 7. p. 81 3-81 4. v. 84, p. 285 1-2872. Wise, Donald U., 1972. Freeboard of continents through time: Geol. — 1973b, Worldwide unconformities in marine sediments related Soc. America Mem. 1 32, p. 87-100. to eustatic changes of sea level: Nature Phys.-Sci., v. 244, 1973, Constant freeboard deviations and the master equilibrium p. 25-26. of tectonics: Geol. Soc. America, Abs. with Programs (Ann. 1973c, Global sea level, plate tectonics and marine stratigraphy: Mtg.), v. S, no. 7, p. 867. 134 MARCH 1974 1093 Reprinted from Journal of Sedimentary Petrology Vol. 44, No. 2, June 1974 pp. 549-552 Made in United States of America © 1974 by The Society of Economic Paleontologists and Mineralogists TIME-LAPSE PHOTOGRAPHY OF THE BIOLOGICAL REWORKING OF SEDIMENTS IN HUDSON SUBMARINE CANYON1 2 GILBERT T. ROWE Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 GEORGE KELLER NOAA Atlantic Oceanographic and Meteorological Laboratories, Miami, Florida 33149 HAROLD EDGERTON Massachusetts Institute of Technology, Cambridge, Massachusetts 02135 NICK STARESINIC and JOE MacILVAINE Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Abstract : Time-lapse photography indicates that biological activity and reworking acted as a catalyst for sediment erosion by bottom currents during a two-day period at a depth of 360 meters in the Hudson submarine canyon. Decapod Crustacea were responsible for the major tracks and burrows. Deep, sharp tracks made by the crab Cancer borealis were smoothed by currents within three hours, but a large burrow was maintained with inter- mittent excavation by a smaller burrowing decapod crustacean. The asteroid (seastar) Henricia did not track but smoothed the bottom. A polychaete worm appeared to forage in the Cancer tracks. Bottom water turbidity varied abruptly at intervals of less than one hour. INTRODUCTION Bottom photography has been a useful tool in the study of deep-sea sediments and bottom fauna. It was from photographs that Heezen, Hollister and Ruddiman (1966) first inferred the importance of the western boundary under- current or "contour" current. Based on bottom photographs, Stanley (1971a, b) and Dillon and Zimmerman (1970) have suggested that a major cause of erosion is animal activity. Unfortu- nately, conventional bottom photography isolates the bottom at a single point in time and space. No rates of erosion can be inferred, but only that it has occurred. To obviate this, we have used time-lapse photography to measure erosion at a single position on the sea floor over a two-day period. This is an initial step in understanding the importance of different mechanisms affect- ing the rates of erosion and reworking of sedi- ments under various conditions. 1 Manuscript received September 6, 1973. 2 Contribution number 3179 from the Woods Hole Oceanographic Institution. This work was supported by National Science Foundation Grant GA 31235X, Office of Naval Research Contract N00014-66-C- 0241, the National Atmospheric and Oceanic Ad- ministration, Department of the Interior and the National Geographic Society. METHODS A 16-mm time-lapse movie camera (Flight Research Model III-B) and flash system (Edgerton, MacRoberts and Read, 1968) de- signed to take pictures underwater for a two- week period were placed in stainless steel hous- ings capable of withstanding pressures of 500 atmospheres. These cases were mounted on an aluminum tripod 3 meters high and 2 meters across at its base. The tripod and camera sys- tem were designed to operate as a free vehicle by mounting 10 glass flotation spheres (40 cm diameters) on the top of the tripod, which made it positively bouyant (ca. 40 kg). This was counter balanced with 90 kg of disposable weights which could be released by an "AMF" acoustic release and transponder on a sonic command from a surface vessel's transducer (Fig. 1). The camera system was initially used off the Woods Hole Oceanographic Institution pier at a depth of 23 m, in the vicinity of the Woods Hole sewage outfall (15 m) and to photograph the animal activity on a small artificial reef constructed of solid refuse in the Woods Hole harbor. Each deployment was successful but poor visibility caused the quality of the photo- graphs to be poor. 1094 550 G. T. ROWE ET AL. 72,3ff 7 2* 00* Fig. 1. — The free vehicle design. A, flotation spheres; B, transponder; C, release mechanisms; D, disposable weights; E, strobe; and F, camera. The first deep-ocean use was at a depth of about 360 m near the head of the Hudson submarine canyon in the mid-Atlantic Bight (39°37.4'N X 72°25.0'W) (Fig. 2). It was deployed, as a complementary part of the DSRV Alvix observations in the canyon, off the cata- maran Lulu, which serves primarily as Alvin's tender. RESULTS The free-vehicle camera unit was deployed from Lulu on September 12, 1972 and re- covered on September 14. During the 42 hour period 582 frames were exposed using an inter- val between exposures of 4.3 minutes. Fifty-six frames, scattered throughout the filming, were blank, because we assume the strobe did not fire. The camera on this particular lowering was positioned one meter off bottom and pointed at a spot one meter out from the tripod base. The field of view was approximately one square meter. The periphery of each frame was poorly lighted which diminished the distinguishable area by about 25%. Such close proximity to the bottom was necessary because of the highly Fig. 2. — Hudson submarine canyon with the loca- tion of the camera deployment. Depths are in fathoms. turbid bottom-water common to this portion of the Hudson canyon axis. The free-vehicle camera unit serendipitously came to rest with a tunnel-like burrow about 3 cm in diameter in the center of the field. Ob- servations were made of the activities in and around this hole, frame by frame. Sediments at this site are clayey silts. The large recognizable animals that crossed the field were the crab Cancer borealis, a sea- star Henricia (probably esditricJiti or per- forata), an eel Synaphobranchus sp., the shrimp Sclcrocrangon, an octopus, and a burrowing decapod crustacean. The total residence time over the 42 hours and the length of continuous time at any given visit for each recognizable species is important information if inferences are to be made as to the degree animal activity influences a given area of bottom. We have therefore counted the total number of times an individual appears and the number of frames each animal appears in a continuous sequence. A Henricia appeared three times on 4, 2 and 4 consecutive frames. The individual on the latter 4 was about 25% smaller in diameter than the one or ones earlier. This indicates it was a different individual, rather than the same one moving back and forth. Cancer appeared at three different times in 2, 1 and 3 frame-. Sclcrocrangon was in two frames and the octopus and ecl were in only one frame each. None of the animals ever appeared together. A burrow- ing decapod, measuring about 3 cm in length, 1095 PHOTOGRAPHY OF BIOLOGIC WORK ON SEDIMENTS 551 appeared on about 15 frames scattered through- out the filming. It was always in or close to the burrow and is presumed to have been the hole's occupant. A total of 41 frames or about 176 minutes were occupied by these megabenthic (or visible) animals over the 42-hour period. Just after Cancer made its 3-frame move across the area, a green worm about 2-3 cm long and several millimeters in diameter moved during 8 frames across the bottom in the opposite direc- tion the crab had gone, going in and out of the sharp, deep grooves left in the mud by Cancer's walking legs. These 34 minutes were the longest any macro fauna stayed before the camera. Small unidentifiable objects, presumed alive, were seen on the bottom in 30 frames, and in 18 frames objects were seen in the water, scat- tered throughout the 42 hours. The deepest, most characteristic tracking was made by the crab Cancer borealis. As it moved sideways across the field, precise slices were made in the sediment about 2 cm long each, parallel to its direction of movement. These were made by its walking legs or peraeopods, but its pincers or chelipeds were kept folded in to its body and made a continuous oval groove in the sediment. This track was made in frame 340. By frame 375, or 2V2 hours later, it was noticeably smoothed by existing currents. More rapid modification occurred in the next two frames resulting in as much smoothing as occurred during the previous 35 frames, sug- gesting the currents had abruptly increased in velocity or that the track, once slightly modified, was more amenable to degradation. The cheliped groove appeared to be transformed into a slight hump or ridge. By the end of the filming the track was still visible, but barely so. Between frame 553 and 554 the water clarity suddenly diminished markedly and the bottom became barely visible. By frame 565, 47 min- utes later, turbidity began to decrease and by 571 the original clarity returned (73 minutes from initiation of turbidity). After this, the burrowing decapod in the hole appeared to be cleaning it out. This apparent excavation may be an artifact, but no such activity occurred before the water became turbid. While the crustaceans were responsible for sediment disturbances such as tracking and burrow maintenance, the movement of the sea- star Henricia across the field left no track but rather smoothed the sediments. Its movements were much slower than the decapods'. The small green worm which seemed to be exploring Cancer's tracks also probably had a smoothing effect, but this was difficult to detect with certainty due to its small size. DISCUSSION The origin and dispersion of deep-sea sedi- ments along the North American east coast has been of considerable recent interest and con- troversy. The thick wedge of sediments compos- ing the continental rise may have its origin from adjacent land masses (Stanley, Sheng and Pedraza, 1971), but there is much evidence that an undercurrent has played a significant role in shaping the rise and in contributing sedi- ments to it which originated in the Permo- Carboniferous red-bed area of the Canadian Maritime Provinces (Heezen, Hollister and Ruddiman, 1966; Needham, Habib and Heezen, 1969; Hollister and Heezen, 1971; Pilkey and Field, 1972; and Zimmerman, 1972). Obviously sediments are dispersed both downslope across isobaths and along contours by currents, but which has predominated is not clear. There is little or no reliable information available on deep-ocean currents and their ability to resus- pend and transport the clays and silts of the continental margin. Likewise the rates and mechanisms of sediment transport down the continental slope are not known. A possibility often overlooked is that biological activity and bottom currents may act synergistically to cause greater sediment transport than either could produce alone. The lapsed-time photographs support this hypothesis, at least for the head of Hudson canyon. The geographical extent and importance of this synergism will be dependent on the intens- ity and variability of currents, sediment texture, and on the abundance and composition of the fauna. Based on our data, the large decapod crustaceans, because of their sharp appendages and highly mobile habits, have greatest im- portance as modifiers (trackers and burrowers), whereas echinoderms tend to smooth surfaces. (Exceptions of course occur, such as burrowing echinoids (urchins) and seastars.) The larger decapods are common in shallow water, but abound along the upper continental slope. These include the red crab Geryon quinqnedens, which has been seen by us inhabiting holes excavated from indurated clay walls of Hudson canyon at 1000 m depth, the lobster Homarus americanus in burrows in the soft fine sediments of the Gulf of Maine basins (250-300 m deep), and the Cancer borealis and galatheid populations which have been mapped off Cape Hatteras between depths of 200 and 1000 m (Rowe and Menzies, 1969). It could therefore be expected 1096 552 C. T. ROIVE ET AL. that the rates of modification we observed could be duplicated anywhere within this upper slope or bathyal zone of 200 to 1000 m if the currents and sediment texture approximate those in the canyon head. Current or water movements could not be observed by the lapsed-time camera as the pic- tures were taken so infrequently (4.3 minute intervals). Earlier current observations nearby (Keller, Lambert, Rowe and Staresinic, 1973) indicated that water moves up and down the canyon's axis. Continuous recordings monitored a flow that was predominantly towards shore, but a summary of isolated Alvin observations and sedimentary evidence suggest that currents and sediments move down or off-shore more frequently. Long-term records on the west coast suggest similar net transport (Shepard and Marshall. 1972). Short-term variations in veloc- ity or direction were probably responsible for the variations in turbidity we observed and attest to the currents' ability to transport sedi- ments. The confinement of currents to up or down the axis and the biotic erosion observed is an indicator that much of the sediment of the continental rise has come through the can- yons of the adjacent continental margin. Whether or not this is a general phenomenon in east coast canyons is not known. At depths greater than 1500 m echinoderms dominate the visible fauna. Lapsed time ob- servations must be used to document animal activities and their influences on the sediments in deeper physiographic provinces. CONCLUSIONS The activities of large decapod crustaceans were a major contributing factor to the high rates of erosion and sediment reworking at the upper part of the Hudson canyon. Tracks how- ever were surprisingly ephemeral and were smoothed appreciably in a matter of hours by bottom currents. Echinoderms tended to smooth the bottom. Bottom water turbidity varied mark- edly over time spans of less than one hour, probably due to small-scale variations in current direction and velocity. Lapsed-time photography in a free-vehicle mode appears to be a reasonable method for the detailed study of deep sea- floor processes. ACKNOWLEDGMENTS The crew of the R/V Lulu and DSR/Y Alvin assisted with launch and recovery of the free vehicle. Mr. Billy MacRoberts worked furiously to get the camera in working condi- tion for deep deployment. Ms. Maureen Downey made the tentative identification of Henricia, the seastar. REFERENCES Edgertox, H., V. E. MacRoberts, axd K. Read, 1968, An elapsed time photographic system for underwater use: YIII Intern. Congr. on High Speed Photograph v, 52 p. Dillox, YV. P., axd H. B. Zimmerman, 1970, Erosion by biological activity in two New England submarine canyons : Jour. Sed. Pe- trology, v. 40, p. 542-547. Heezex, B. C, C. D. Hollister, axd VY. F. Ruddi- max, 1966, Shaping of the continental rise by deep geostrophic currents: Science, v. 152, p. 502-508. Hollister, C. D., axd B. C. Heezex, 1971, Geologic effects of ocean bottom currents, western North Atlantic: in Gordon, A. L. (cd.), Studies in phvsical oceanoarraphv, New York, Gordon and Breach Publ., v. 2, 232 p. Keller, G. H, D. Lambert, G. T. Rowe, axd N. Staresixic, 1973, Bottom currents in the Hud- son canyon: Science, v. 180, p. 181-183. Needham, H. D., D. Habib, axd B. C. Heezex, 1969, Upper Carboniferous polynomorphs as a tracer of red sediment dispersal patterns in the northwest Atlantic : Tour. Geologv, v. 77, p. 113-120. Pilkey, O. H., axd M. E. Field, 1972, Lower con- tinental rise east of the middle Atlantic states : predominant sediment dispersal perpendicular to isobaths. Discussion : Geol. Soc. America Bull., v. 83, p. 3537-3538. Rowe, G. T., axd R. J. Mexzies, 1969, Zonation of large benthic invertebrates off the Carolinas : Deep-sea Research, v. 16, p. 531-537. Shepard, F. P., and N. F. Marshall, 1972, Cur- rents along floors of submarine canyons: Am. Assoc. Petroleum Geologists Bull., v. 57, p. 244- 264. Stanley, D. J., H. Shexg, axd C. P. Pedraza, 1971, Lower continental rise east of the Middle Atlantic states. Predominant sediment dispersal perpendicular to isobaths : Geol. Soc. America Eull., v. 82, p. 1831-1840. Stanley, D. J., 1971a, Bioturbation and sediment failure in some submarine canyons : Yic et Milieu, suppl. 22, p. 541-555. , 1971b, Fish produced markings on the outer continental margin east of the Middle Atlantic states: Jour. Sed. Petrology, v. 41, p. 159-170. Zimmerman, H. B., 1972, Sediments of the New England Continental Ri>e: Geol. Soc. America Bull., v. 83, p. 37U9-3724. 1097 Vol. 1, No. 8 GEOPHYSICAL RESEARCH LETTERS December 1974 RAPIDLY ACCUMULATING MANGANESE DEPOSIT FROM THE MEDIAN VALLEY OF THE MID-ATLANTIC RIDGE Martha R. Scott, Robert B. Scott Department of Oceanography and Department of Geology, Texas A & M University College Station, Texas 77843 Peter A. Rona, Louis W. Butler NOAA, 15 Rickenbacker Causeway, Miami, Florida 33149 Andrew J. Nalwalk Marine Sciences Institute, University of Connecticut, Groton, Connecticut 06340 Abstract A manganese oxide crust from an ex- tensive deposit in the median valley of the Mid- Atlantic Ridge was found to be unusually high in manganese (up to 39.4% Mn) , low in Fe (as low as ..017. Fe), low in trace metals and deficient in Th230 and Pa231 with respect to the parent uran- ium isotopes in the sample. The accumulation rate is 100 to 200 mm/105 y, or 2 orders of magni- tude faster than the typical rate for deep-sea ferromanganese deposits. The rapid growth rate and unusual chemistry are consistent with a hydrothermal origin or with a diagenetic origin by manganese remobilized from reduced sediments. Because of the association with an active ridge, geophysical evidence indicative of hydrothermal activity, and a scarcity of sediment in the sampling area, we suggest that a submarine hot spring has created the deposit. Introduction Typical deep-sea ferromanganese nodules and crusts grow at a rate of about 1-10 mm/icf years and have an Fe to Mn ratio of .5 to 2. A man- ganese crust recently recovered from the median valley of the Mid-Atlantic Ridge has a growth rate two orders of magnitude faster than the typical rate and an extremely low iron concentra- tion; it appears to have formed under conditions which are not typical of deep-sea manganese de- position. The location of the sampling site and the nature of the material immediately bring to mind a possible association between this mangan- ese oxide deposit and the recently developed Ideas concerning hydrothermal activity along act- ive ridge crests [Anderson, 1972, Lister, 1972 and 1974; Deffeves. 1970; Dymond et .al. ,1973] . According to these theories seawater has perco- lated Into the ocean crust and returned to the •ea floor as hydrothermal solutions, heated and laden with dissolved metals; these fluids may be the source of the metal enrichment of sediments along ridge crests [Bostrom and Peterson, 1969; Bender et.al. . 1971]. Hovever, it has also been suggested LTurekian and Bertine, 1971] that or- ganic-rich sediments may exist in ephemeral sedi- ment ponds along ridge crests and cause enrich- ment of sediments in Mo and U. Conceivably re- mobilization of sedimentary manganese could also occur under such circumstances. The purpose of Copyright 1974 by the American Geophysical Union. this paper is to examine the chemistry and physi- cal surroundings of the sample to determine its probable origin. Sample Description and Location The rapidly growing MnOg crust (sample 13-21) described in this paper was recovered from Dredge site 13 in the Median Valley of the Mid-Atlantic Ridge at 26°N (Fig.l). It was collected during the 1972 Trans-Atlantic Geotraverse (TAG) pro- gram of the National Oceanic and Atmospheric Ass- ociation fR-Scott et.al. ,1974] . Dredge site 13 is a talus slope under 3.4 km of water at the base of the median valley scarp, only 5 km from the median valley axis. Sample 13-21 is a 42 mm thick manganese oxide deposit of blrnessite and a trace of todorokite; the sea water interface Is preserved and clearly identifiable. The mat- erial has a gray submetallic luster and conspicu- ous laminations 5 to 10 mm thick; some layers are very porous and exhibit bladed growth structures. Typical manganese crusts from sites 10G and 2B were also analyzed. Both are brownish -black with a dull earthy luster and uneven 1 to 5 mm lamina- tions. Analytical Methods Radiochemical analyses were carried out by a method similar to that of Ku and Broecker (1969). 60 I 43 I 30 I I0G v//* -MAR — 30 Figure 1. Sample locations for sample 13-21 and for typical manganese crusts from 10G and 2B. 355 1098 356 Scott et al.: Manganese Deposit from Mid-Atlantic Ridge Table la . Radiometric data for manganese crusts; typical crusts from the Atlantis Fracture Zone (Scott et al, 1972). Sample and Interval (mm) U (ppm) Activity Ratio U' /IT Th232 (ppm) Th']" Excess (dpm/g) 2B2-1 0-0.33 2B2-2 .33-. 67 2b2-3 . 67-. 98 10G-1 0-.46 10G-2 .46-. 90 10G-3 .90- •1.39 13.76±.37 18.101.40 16. 20+. 42 12.78±.41 11.62±.29 11.52±.38 1.20±.04 1.02±.03 1.15±.04 1.12±.04 1.22±.04 1.02±.04 218.54±6.65 146.39±20.66 93.35±2.62 159.77+4.52 98.33±3.48 77.86±3.41 417.7H0.5 6.4*1.59 0.68±.59 530.86+11.92 217.48+5.67 104.84+3.55 Thin layers were scraped from the samples, dis- solved in HCl-HNO, , and spiked with Th, U and Pa tracers. Isotopes were separated by ion exchange resins and deposited from organic scavenging so- lutions onto stainless steel planchets. Th and U isotopes were counted by alpha spectrometry using surface barrier solid state detectors and a multi- channel pulse height analyzer; Pa isotopes were counted with a flow-type proportional counter. The results are listed in Table 1. Sample 13-21 dissolved completely; 10G and 2B yielded 5-107. insoluble residue. Analyses for Fe, Mn, Co, Ni and Cu were made by atomic adsorption spectrophotometry. Using an HCI-HNO3 sample solution procedure, the one sigma precision error is 27, of the Mn values, 37. of Fe, 57. of Co, 57, of Ni and 37. of Cu. Results are listed in Table 2. Discussion Radiochemical analysis of uranium series iso- topes shows the site 13 manganese deposit to be very unusual in comparison to typical ferroman- ganese crusts such as those from nearby dredge sites 2B and 10G fScott et.al. ,1972] , (Table 1; Figures 2 and 3). Manganese deposits found in the deep sea ordinarily contain amounts of Tha3° and Pa331 far in excess of the amounts of equili- brium with the parent uranium isotopes [Ku and Broecker, 1969; Sackett, 1966], indicating that thorium and protactinium have been scavenged from sea water during the process of manganese accumu- lation. In contrast to the expected excess of Th2'30 and Pa331, sample 13-21 was strikingly de- ficient in these isotopes relative to secular equilibrium with uranium. Commonly, manganese accumulation rates are measured by the decay of excess or unsupported Th230 and Pa331. Because of the absence of these isotopes from the deposit, the accumulation rate was measured from the growA rate of Th330 and Pa231 toward secular equilibrium with their uranium parents. Growth of Th230 and Pa231 give independent measures of the accumula- tion rate, and the two determinations are in rea- sonably good agreement, Th230 yielding 130 mm/lcPy and Pa231 showing 250 mm/icfy (Fig. 3). The Th data are clearly more precise. The ages for layers of sample 13-21 (Table 1) are maximum ages calculated with the assumption that all the Th230 and Pa231 have grown in from the uranium in the sample. The apparent ages of surface material indicate that some small amounts of thorium and protactinium are scavenged by the rapidly accumulating manganese; the very low activity of these isotopes in the surface layer Table lb. Radiometric data from manganese crusts; sample 13-21 from the median valley of the Mid-Atlantic Ridge. One sigma errors from counting statistics are listed. Sample and U Activity Th232 Activity Activity Max. ages (xl03y) Interval Ratio Ratio Ratio from growth of (mm) (ppm) U231,/U23e (ppm) Th230/U23" Pa231/U235 Th230 and Pa231 13-21-1 16.46±.39 1.06±.03 2. 50+. 28 .1351.010 .125+. 034 15.711. 2 6.3+1.7 0-.51 13-21-2- 13.211.44 1.121.04 3.271.35 .1601.014 .51-. 91 13-21-3 .91-1.41 13-21-4 1.41-3.01 13-21-5 3.01-4.61 13.611.70 1.231.07 4.541.66 .2251.023 8.951.28 1.161.04 2.341.58 .2331.033 9.251.41 1.131.06 3.951.29 .3361.021 1311.060 18.911.6 6.613.0 188+.073 27.8+2.9 9.813.8 2471.093 28.814.1 13.315.0 44.512.8 1099 Scott et al . : Manganese Deposit from Mid-Atlantic Ridge 357 Table 2. Compositions of layers within the largest fragment of the Site 13 manganese deposit (sample 13-21); the typical f er r omanganese crusts from dredge sites 10G and 2B, and from sites 19 and 15 within 50 km of site 13; and the average Pacific and average Atlantic nodules, (Bonatti e_t a_l 1972). The compositions listed for sites 10G and 2B are averages of four samples (Scott e_t a_l 1972). Composition Sample L oca tion 26°08 'N, 44 '45 W a top 5 mm b 6 mm c 6 mm d 5 mm e 3 mm f 8 mm S 8 mm Mn(Z) Fe(X) Co(ppm) Hi(ppm) Cu(ppm) T3-72D 253-13-21 Sequence of samples through layers of 13-21 T3-71D 160-10G T3-71D 143-2B T3-71D 254-15-2 T3-72D 255-19-3 Average Pacific nodules Average Atlantic nodules 30°08'N, 42°29*W 26°07*N, 25°21*W 26°33.9'N, 44°30'W 26°16.9'N, 45°6.3'W 39.2 0.011 18 100 12 38.5 0.078 25 790 119 38.6 0.106 25 660 93 39.4 0.070 20 200 23 39.2 0.072 18 400 23 39.1 0.038 16 270 19 39.3 0.036 14 50 11 9.8 18.1 2720 1280 880 14.1 16.1 7200 2200 750 11.2 16.4 9480 900 300 11.0 18.6 4950 1110 405 19.8 14.3 3810 7200 3660 16.2 21.8 3090 3970 1090 make it difficult to determine accurately the ra- tio in which the Th and Pa were incorporated. The growth rate of 13-21, about 200 mm/lO^y, la two orders of magnitude faster than the typi- cal growth rates for marine ferrotnanganese depo- sits. For example, the decay curves of excess Th330 with depth in the deposits from sites 2B and 10G yield growth rates of 1 and 5 mm/106 y, respectively, typical of rates found in other deep-sea manganese deposits (Ku and Broecker, 1969). The major and trace element composition of this Mid-Atlantic Ridge manganese deposit is dis- tinctly different from that of typical deep-sea ferrotnanganese nodules (Table 2); this sample is practically pure manganese oxide with as little •8 0.01 weight X Fe. In addition the Cu, Ni, Co and Th contents are quite low compared to typical deep-sea hydrogenous deposits, including hydro- genous crusts collected within 50 km of site 13 (Tables 1 and 2). This appears to be character- istic of rapidly growing manganese deposits; the more slowly the material accumulates, the higher its concentration of certain trace metals removed from sea water fBonatti et.al. , 1972 ] regardless of the source of the manganese. The same effect may be seen in the low trace metal contents of the Loch Fyne and Jervis Inlet nodules [Ku and Glasby, 1972]. However, this generalization does not hold for all trace elements. Uranium, for example, does not appear to be affected by rapid growth rates (Table 2; Ku and Glasby, 1972), and its mechanism of incorporation into manganese deposits may differ from the other elements list- ed. The U334/^38 activity ratios for all the layers of 13-21 are essentially the same as sea water, 1.15 within limits of counting errors (Table 1); the uranium in this deposit was prob- ably incorporated from sea water. The rapid growth rate, low trace metal content, extreme fractionation of Mn from Fe, and low sur- face ratios Th330/^34 and Pa331/!)336 reported for sample 13-21 may typify either hydrothermal deposits such as the one described by Veeh and Bostrom (1971) from a Pacific seamount, or depo- sits formed by manganese remobilized from re- duced sediments fKu and Glasby, 1972; Manheim, 1965], The overlapping chemical characteristics a; Figure 2. Rates of manganese crust accumulation based on decay of Th33" excess; a. 10G. b. 2B. ■b I y 250«mii/I(A Fig 56 Figure 3. Rate of accumulation of site 13 mangan- ese deposit, a. Rate from growth of Th330;b.Rate from growth of Pa231. Lines are best fit lines. 1100 358 Scott et al.: Manganese Deposit from Mid-Atlantic Ridge of these two types of deposits were pointed out by Bonatti et.al.,1972 ; but this Mid-Atlantic Ridge crust has much higher Mn/Fe ratios (360 to 3600) than values published for diagenetic con- tinental margin nodules [Ku and Glasby, 1972; Manheim, 1965] Bottom photographs show that the current- swept talus slope from which sample 13-21 was dredged is essentially sediment-free; the sample itself was recovered from a site at least 500 m above the median valley floor. Subsequent dredg- ing of the site always yielded more thick MnO^ encrustations; away from this site, pillow basalts were dredged but no thick MnOg crusts were found. Other work on the sampling site showed it to have a sharp 0.14°C increase in bottom water tempera- ture over the site [Rona et . al . , 1974] and very iron-rich suspended matter in the overlying water column [Betzer et . al . , 1974n . Moreover, the Brunhes normal axial magnetic anomaly contains a..localized magnetic low region which coincides with the sampling site, and which may reflect hydrothermal alteration of magnetic minerals in the pillow lavas [Watkins and Paster, 1971]. These features combined with other lines of evi- dence suggesting hydrothermal activity along active ridge crests [Anderson, 1972; Lister, 1972 and 1974; Dymond et.al.,1973] have led us to con- clude that the MnOg crust described in this paper was deposited by a hydrothermal spring in the median valley of the Mid-Atlantic Ridge, rather than forming as a diagenetic deposit. The region itself has been described elsewhere as the TAG Hydrothermal Field [Scott et .al. ,1974] . The extreme fractionation of Mn from Fe in sample 13-21 probably resulted from the differen- tial solubilities of the two elements during oxi- dation by sea water oxygen [Krauskopf , 1958], Iron in hydrothermal fluids may have been precipi- tated at lower levels within the pillow lavas or the talus as oxides or sulfides; but some iron apparently bypassed both the pillow lavas and the surface deposit to have become suspended in the water column [Betzer et .al . , 1974] . An attempt to evaluate the magnitude of chemi- cal effects due to hydrothermal effluents upon the composition of sea water would require esti- mates of the numbers of submarine hydrothermal orifices, the rate of flow from each, and the com- position of the fluids of each. Obviously these data are absent at present. The nature and extent of possible hydrothermal deposits beneath the Atlantic and Indian Oceans, where slow spreading favors ocean water circulation in the crust, need to be evaluated. Acknowledgements. Our research was supported by NSF grants GA-35456 and GA-29370 and by ONR Contract N00014-68-A-0308-0002 . References Anderson, R.N., Petrological significance of low heat flow on the flanks of slow-spreading mid- ocean ridges, Geol.Soc.Amer .Bull . ,83,2947- 2956,1972. Bender, M. , W. Broecker, V. Gornitz, U. Middle, R. Kay, S.-S Sun and P. Biscaye, Geochemistry of three cores from the East Pacific Rise, Earth and Planet. Sci.Lett. 12, 424-433,1971. Betzer, P.R., G.W. Bolger, B.A. McGregor and P. A. Rona, The Mid-Atlantic Ridge and its effect on the composition of particulate matter in the deep ocean (Abstract), Eos Trans. A.G.U.,55, 193,1974. Bonatti, E., T. Kramer, and H.S. Rydell, Class- ification and genesis of submarine iron-mangan- ese deposits, in Ferro-manganese Deposits on the Ocean Floor, pp 146-166, Lamont-Doherty of Columbia University, Palisades, N.Y. 1972 . Bostrom, K. , and M.N. A. Petersen, The origin of aluminum-poor ferromanganoan sediments in areas of high heat flow on the East Pacific Rise, Marine Geology, ]_, 427-447, 1969. Deffeyes, K.S., The axial valley: A steady state feature of the terrain, in Megatectonics of Continents and Oceans, pp 194-222, Rutgers University Press, New Brunswick, N.J. , 1970. Dymond, J.D. , J.B. Corliss, G.R. Heath, C.W. Field, E.J. Dasch, H.H. Veeh, Origin of metalliferous sediments from the Pacific Ocean, Geol. Soc. Amer. -Bull., 84, 3355-3372, 1973. Krauskopf, K.B. , Separation of manganese from iron in sedimentary processes, Geochim.Cosmo- chim.Acta, 12, 61-84,1958. Ku, T.-L., and W.S. Broecker, Radiochemical stud- ies on manganese nodules of deep sea origin, Deep-Sea Research, _16, 625-637, 1969. Ku, T.-L, and G.P. Glasby, Radiometric evidence for rapid growth rate of shallow-water contin- ental margin manganese nodules, Geochim. Cos- mochim. Acta, 36., 699-704,1972. Lister, C.R.B., On the thermal balance of a mid- ocean ridge, Geophys. J.R. Astr. Soc, 25, 515-535,1972. Lister, C.R.B., Water Percolation in the Ocean Crust, Eos. Trans. A.G.U., 740-742, 19 74. Manheim, F.T. , Manganese-iron accumulations in the shallow marine environment, Narragansett Mar. Lab. Publ. 3-1965, pp 217-276, University of Rhode Island, Kingston, Rhode Island, 1965. Rona, P.A., B.A. McGregor, P.R. Betzer, D.C. Krause , Anomalous water temperatures over Mid- Atlantic Ridge crest at 2*6°N (abstract), Eos Trans. AGU, 55, 193, 1974. Sackett, W,M. , Manganese nodules: thorium-230: protactinium-231 ratios, Science, 154,646-647, 1966. Scott, R.B., P. A. Rona, L.W. Butler, A.J. Nalwalk, and M.R. Scott, Manganese crusts of the Atlan- tic fracture zone, Nature Phys. Sci. ,239, 1972. (see erraturm for this paper: Nature Fhys.Sci. 242,95,1973.) Scott, R.B., P. A. Rona, B.A. McGregor and M.R. Scott, The TAG Hydrothermal Field, Nature, 251, 301-302,1974. Turekian, K.K., and K.K. Bertine, Deposition of molybdenum and uranium along the major ocean ridge systems, Nature, 229, 250, 1971. Veeh, H.H., and K-. Bostrom, Anomalous Us34/Ue38on the East Pacific Rise, Earth Planet. Sci.Lett. \0, 372-374, 1971. Watkins, N.D., and T.P. Paster, The magnetic prop- erties of igneous rocks from the ocean floor, Phil. Trans. Roy. Soc. Lond. A., 268, 507-550, 1971, (Received October 4, 1974; accepted November 8, 1974.) 1101 (Reprinted from Nature. Vol. 251, No. 5473, pp. 301-302. September 27, 1974) The TAG hydrothermal field There is abundant evidence that seawater penetrates, and circulates within, the oceanic crust at active spreading centres. Low heat flow values from ridge crests imply that heat must be removed locally by water circulation'"'. Furthermore, hydrous metamorphosed oceanic crust and oceanic serpentines, which required voluminous quantities of water during their formation7"', also have isotopic com- positions which indicate that the isotopic sources had low £'"0 values, such as are found in seawater10. The tectonic setting of strike-slip and normal faulting along the rift valley scarps of oceanic ridges is conducive to the penetra- tion of dense, cold water down the fractures, the heating of the water at depth, and the exhalation of the less dense hydrothermal water as submarine springs along fracture systems. During the 1972 and 1973 cruises of the Trans-Atlantic Geotraverse (TAG) project of the National Oceanic and Atmospheric Administration (NOAA), extensive bathy- metric and geophysical surveys, and dredging, were car- ried out on an area two degrees square between the Kane 2b :I5'N 44 42 W 2b Oil S Pig. 1 Location of the 1972 and 1973 dredge sites from which hydrothermal manganese was recovered. This region covers part of the rift valley in the upper left corner, the eastern wall of the rift valley and a part of the eastern ridge crest highlands" J\ Contours arc in hundreds of metres. The TAG hvdrothermal field is shown within the solid straight lines which enclose an area of approximately 100 kmJ. and the Atlantis Fracture Zones on the Mid-Atlantic Ridge at 26° N. The usual assemblage of pillow basalts, metamorphosed pillow basalts, diabases and gabbros were dredged from scarps within 20 km of the distinct rift valley". Along one section of the eastern wall of the rift valley, however, every dredge recovered thick hydrothermal manganese encrustations that overlie and cement underlying talus (Fig. 1 ). Several lines of evidence suggest that this region is an active hydrothermal field. ) hydrogenous ferromanaganese nodule are from Price and Calvert". The two hydrogenous ferro- manganese crusts were collected from within 50 km of the hydrothermal field. Submarine, hydrothermal ferro- manganese deposits have been reported from seamounts, submarine volcanoes, and the Afar and Red Sea spreading centres". The manganese deposit is more than 50 mm thick but is found only 3-8 km from the median axis of the valley and thus must have grown about two orders of magnitude faster than typical open ocean, hydrogenous ferro- manganese deposits. Rapid growth has been confirmed by i:oTh/-uU and JJ1Pa/2"U data which indicate growth rates of 130-250 mm per 10s yr respectively". The possibility that this rapid growth could be the result of a remooilisation of manganese in reduced, organic-rich, ponded sediment13" is unlikely, because photographs of the ocean bottom1' show the hydrothermal deposit growing on essentially bare, current swept talus 500-1,500 m above the rift valley floor. Chemically, the deposit is within the hydrothermal region (Fig. 2), and mineralogically it consists primarily of birnes- site and secondarily of todorokite13-17. A positive thermal anomaly (0.14° C) was found in the water column over the hydrothermal region". Also, the suspended weak-acid-soluble particles rich in iron and manganese, which were collected over the hydrothermal site, are far more concentrated than similar particles found to either side of the ridge crest1'. Photographs show en- crustations covering only the talus slopes". Magnetic sur- veys indicate that the Brunhes normal axial anomaly con- tains a magnetic low region, the boundaries of which coincide closely with other estimations of the hydrothermal field boundaries" •" (Fig. 3). Presumably, the hydrothermal alteration of the magnetic mineral component of the pillow lavas has greatly reduced intensity of magnetisation10. Perhaps most significant, this observation of a distinctive magnetic irregularity associated with hydrothermal activity 1102 m.i\ become the geophysical exploration tool for the r.ip;J location of new oceanic hydrothermal sites. K-nvmancanese deposits and ferromanganese-rich sedi- ments at the interface of basalts and overlying sediments .,ri- common features of ophiolites21"" Petrological evidence invests that some ophiolites may have been formed off SE NW Department of Geology, Texas A & M University, College Station. Texas 77843 20 40 40 Distance (km) Bjihvmetn |m) Magnetic anomaly (gammas1 Fig. 3 Bathymetric and residual magnetic profiles across the rift valley of the Mid-Atlantic Ridge near 26°N (refs 15 and 35). a, 12 km north of the TAG hydrothermal field, showing the strong Brunhes normal over the axial \jllev. which is typical of all of our profiles from outside (ho h>drothermal field; b, profiles across the TAG hydro- thermal field; the arrow indicates the magnetic low in the axial anomaly. ridge axes""", suggesting that hydrothermal mineralisation could occur away from a ridge axis. In any case, this does not detract from the probability that the hydrothermal mechanisms that operated in many ophiolitic complexes to form cupreous pyrite bodies"""", altered pillow lavas, and overlying manganiferous oxides, were similar to that now operating on the Mid-Atlantic Ridge at 26°N. Although massi\e sulphide bodies have not yet been recovered from this site, disseminated pyrite occurs in greenstone pillow lavas dredged from adjacent fault scarps. Sulphide deposits are not rare in altered oceanic rocks30 ". Thus, we infer that the TAG hydrothermal field may at present be form- ing Troodos-type, massive, stratiform, sulphide bodies within pillow lavas below the manganese deposits. The sharp transition from the precipitation of metal sulphides to the precipitation of metal oxides at the sea- water-basalt interface is probably controlled largely -by a sharp gradient of oxygen concentration from hydrothermal fluids which have little oxygen, to bottom waiters which have relatively high concentrations of oxygen. A reasonable climate of the fugacities of oxygen, and sulphur, and of the r>H values that may operate in such a system, has been given by Meyer and Hemley" The source of sulphur in these hydrothermal systems may in part be reduced sul- phate from the influxed seawater, but some sulphur is probably leached from rocks that react with hydrothermal fluids (unpublished work: fresh pillow lavas, 1,000 p. p.m. sulphur; adjacent greenstones. 400 p. p.m. sulphur). The iron and manganese are probably leached from crustal rocks under low /O.. conditions; much of the dissolved iron may be removed from fluids as sulphides at lower tempera- tures close to the surface, but a significant quantity be- comes suspended in the ocean water column". Because the iron readily precipitates as hydroxides at lower oxygen concentrations than manganese compounds", the particulate iron phase must bypass the manganese crust at the TAG hydrothermal field. The work was supported financially by NOAA and by the National Science Foundation. Robert B Scott Peter A. Rona Bonnie A. McGregor Martha R. Scott National Oceanic and A tmospheric A dminist ration , 15, Rickenbacker Causeway. Miami, Florida 33149 Department of Oceanography, Texas A & M University Received May 20, 1974. 1 Anderson, R. N., Bull. geol. Soc. Am., 83, 2947 (1972). 2 Lister, C. R. B.. Geophys. J. R. astr. Soc, 25, 515 (1972). J Deffeyes, K. S., in Megatectonics of Continents and Oceans, 194' (Rutgers Universitv Press, New Brunswick, 1970). 4 Palmerson, G , in Iceland and Mid-Ocean Ridges (edit, by Bjornsson, S.), Ill (Visindafelag Islendinga, 1967). ' Williams, D. L., Von Herzen, R. P., Sclater, J. G., and Anderson, R. N , Geophys. J. R. astr. Soc. (in the press). 6 Sclater, J. G., Von Herzen', R. P., Williams, D. L., Anderson, R. N., and Klitgord, K. D., Geophys. J. R. astr. Soc. (in the press). 7 Miyashiro, A., Shido, F., and Ewing, M., Phil. Trans. R. Soc, A268, 589 (1971). ' Miyashiro, A., Shido, F., and Ewing, M., Contr. Miner. Petrol., 23, 38 (1969). 9 Christensen. N. I., J. Geol.. 80, 709 (1972). 10 Muehlenbachs, K., and Clayton, R. N., Can. J. Earth Sci., 9, 471 (1972). " Scott, R. B.. Hajash. A., Kuykendall, W. E., Rona, P. A., Butler, L. W., and Nalwalk, A. J., Trans. Am. geophys. Un., 54, 249 (1973). u Scott, M. R., Scott, R. B., Nalwalk, A. J., Rona, P. A., and Butler, L. W., ibid., 54, 244 (1973). 13 Ku, T. L., and Glasby, G. P., Geochim. cosmochim. Acta, 36, 699 (1972). " Bertine, K. K., and Turekian, K. K., ibid., 37, 1415 (1973). " McGregor, B. A., Rona, P. A., and Krause, D. C, Trans. Am. geophys. Un., 55, 293 (1974). " Bonatti, E., Kramer, T., and Rydell, H. S., in Ferromanganese Deposits of the Ocean Floor, 149 (Lamont-Doherty of Columbia University, Palisades, 1972). 17 Scott, R. B., Scott. M. R., Swanson, S. B., Rona, P. A., Butler, L. W., and McGregor, B. A., Trans. Am. geophys Un., 55, 293 (1974). " Rona, P. A., McGregor, B. A., Betzer, P. R., and Krause, D. C, ibid., 55, 293 (1974). " Betzer, P. R., Bolger. G. W., McGregor, B. A., and Rona, P. A., ibid., 55, 293 (1974). 30 Watkins, N. D . and Paster, T. P., Phil. Trans. R. Soc, A268, 507 (1971). 21 Wilson, R. A. M., and Ingham, F. T., Mem. geol. Surv. Dep. Cyprus, I (1959). 23 Robertson, A. H. F., and Hudson, J. D., Earth planet. Sci. Lett.. 18, 93 (1973). 25 Spooner, E. T. C, and Fyfe, W. S., Contr. Miner. Petrol, 42, 287 (1973). " Miyashiro, A., Earth planet. Sci. Lett., 19, 218 (1973). 25 Strong, D. F., ibid., 21, 301 (1974). " Karig. D. E., J. geophys. Res., 76, 2542 (1971). 27 Upadhyay, H. D., and Strong, D. F., Econ. Geol., 68, 161 (1973). " Hutchinson, R. W„ ibid.. 68, 1223 (1973). " Constantinous, G., and Govett, G. T. S., ibid., 68, 843 (1973). " Dmitriev, L. V., Barsukov, V. L., and Udinstev., G. B., Geokhimiya, 4, 93 (1970). 31 Bonatti, E.. Honnorez, I., and Guerstein, M. H., Trans. Am. geophys. Un., 55. 455 (1974). 32 Meyer, C, and Hemley, J. J., in Geochemistry of Hydro- thermal Ore deposits (edit, by Barnes, H. L.), Fig. 6.9, 220 (Holt Rinehart, Winston. New York, 1967). 33 Krauskopf, K. B., Geochim. cosmochim. Acta, 12, 61 (1957). 34 Price, N. H , and Calvert, S. E., Mar. Geol., 9, 145 (1970). 35 McGregor, B. A., and Rona, P. A., /. geophys. Res. (in the press). Printed in Great Britain by Henry Ling Ltd., at tha Dorset Preu. Dorcheiter, Dorset 1103 MESA Report No. 1 RECONNAISSANCE OF BOTTOM SEDIMENTS ON THE INNER AND CENTRAL NEW JERSEY SHELF (MESA Data Report) William L. Stubblefield Michael Dicken Donald J. P. Swift MARINE ECOSYSTEMS ANALYSIS PROGRAM Boulder, Colorado July 1974 UNITED STATES DEPARTMENT Of COMMENCE Frederick B. Dent, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M White. Administrator Environmental Research Laboratories Wilmot N. Hess, Director For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402 1104 DISCLAIMER The NOAA Environmental Research Laboratories do not approve, recommend, or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to the NOAA Environmental Research Laboratories , or to this publication furnished by the NOAA Environmental Research Laboratories, in any advertising or sales promotion which would indicate or imply that the NOAA Environmental Research Laboratories approve, recommend, or endorse any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NOAA Environmental Research Laboratories publication . 1105 CONTENTS Page ABSTRACT 1 INTRODUCTION 1 METHODS 5 Field Methods 5 Laboratory Techniques 5 TABULAR RESULTS 9 SUMMARY 14 REFERENCES 15 1106 RECONNAISSANCE OF BOTTOM SEDIMENTS ON THE INNER AND CENTRAL NEW JERSEY SHELF (MESA DATA REPORT) William L. Stubblefield1 Michael Dicken2 Donald J. P. Swift1 ABSTRACT The petrography of samples from two areas on the New Jersey Shelf was analyzed to resolve the relation between sur- ficial grain-size distribution, hydraulic regime, and bathy- metry. Determination of this relation is essential to our understanding of the sediment flux in these areas and is a critical parameter for environmental impact problems. The sample localities are presently undergoing, or are being considered for, a variety of conflicting usages, including food resources (fishing), mineral resources (beach borrow), and waste disposal (dredge spoil and sewage). All of the collected samples were examined for grain- size distribution in quarter-phi intervals and for related statistical parameters which include mean grain size, standard deviation, skewness, and kurtosis. A mean grain- size distribution map for each area suggests a relation between bathymetry and grain-size distribution which, in turn, defines certain features of a hydraulic regime. Selected samples were further examined for relative per- cent of detritus , clay pebbles , fauna content , and heavy mineral concentrations. The individual petrographical parameters are presented in tabular form. INTRODUCTION During the period 1972-73, the bottom sediments of two study areas (areas 1A and IB) on the New Jersey Shelf were sampled 1MESA, Atlantic Oceanographic and Meteorological Laboratories, Miami, Fla. 33149. 2Dept. of Earth Sciences, Queens College, Flushing, N. Y. -11367. 1107 and analyzed in support of the NOAA MESA (Marine Ecosystems Analysis) program (fig. 1). The study areas were selected as: (1) areas critical to the natural system of cohesionless sediment (sand) flux; and (2) areas presently or potentially experiencing environmental impact problems. Both areas (fig. 2) lie on the Great Egg Shoal Retreat Massif, the retreat path formed during the Holocene sea level rise of a littoral- drift convergence zone associated with the Ancestral Great Egg River mouth (Swift and Sears, 1974, in .press). During the near-stabiliza- tion of sea level rise in the late Holocene, a prominent inner shelf ridge field (fig. 2) developed in- the Atlantic City, N. J. , study area (Duane et al. , 1972). The Atlantic City area is presently experiencing environmental management problems relating to beach erosion, sewage disposal, and fishing. The first offshore nuclear powerplant, off Beach Haven Inlet (fig. 2), is scheduled to be built within the Atlantic City study area. In the Central New Jersey Shelf study area (IB), a ridge-and-swale topography has been impressed on the Great Egg Shoal Retreat Massif subsequent to the retreat of the shoreline (Swift et_ al . , 1973). This ridged central shelf sector is believed to be representative of many areas that are potential sites for offshore waste disposal. Bottom sediment samples from the study areas are described in this report. For a more detailed and interpretative report on some of these data, see Stubblefield et al. (1974, in press). 1108 < Figure 1. Sample looalities for NOAA Marine Ecosystems Analysis Program (MESA). 1109 / 39° 00 N\, £ ^ < / 38° 45' N\ / \ — 7V 74°00'W — T~ 73°45'W "X" : FIRST ORDER HIGHS *-— " CRESTLINES, SECOND ORDER HIGHS • PROSPECTIVE SITE OF NUCLEAR POWER PLANT Figure 2. Sample areas 1A and IB. 1110 METHODS Field Methods The grab samples collected from the nearshore area of the New Jersey Shelf are denoted by prefix "1A" and bounded by latitudes 39°17'N and 39°30'N; longitudes 74°09'W and 74°21'W. The area, 40 km off the New Jersey shore, is denoted by prefix "IB" and bounded by latitudes 39°00'N and 39°10'N; longitudes 73°45'W and 74°00'W (fig. 2). Navigation was provided by dual, automatic-tracking Loran A receivers for all of 1A samples and the bulk of IB samples. Samples from 375 through 407 and from 449 through 492 were collected, using Raydist electronic control which affords much improved navigational accuracy over Loran A. The expected navigational error in the respective systems ranges from ± 600 m using Loran A to t 10 m utilizing Raydist. Shipek grab samples were collected every 800 m on the cruise which used Loran A coverage and every 400 m when Raydist was utilized. In each area, the sample transects were both normal and parallel to the major bathymetric features (fig. 3 and 4). In the western sector of area IB, where a maximum ridge slope is found, a more dense sample net normal to the bathymetry was effected. The latitude and longitude coordinates for each sample station are presented in table 1. Laboratory Techniques Shipek grab samples were split from 1-kg to approximately 60 g by using either a sampler splitter or the random scoop method suggested 1111 Fiqure 3. Sample net for area 1A superimposed on bathymetry. The solid dots denote a sample station. Bathymetry is in 1-fm. contours. 1112 39°15' 39°10' 39°05' 39°00'N 74°00W 73°55' 73°50' 73°45' Figure 4. Bathymetry of area IB. The Shipek grab samples are shown as dots and vibracores as squares. The sample numbers appear beside the position. (From Stubblefield et al.3 1974.) 1113 by Shepard and Young (1961). The 60-g sample split was dry-sieved, using a 3-in. (76-mm) U.S. Standard Sieve to separate the material that was coarser than 2 mm. The sand-and-silt fraction was weighed on a top-loader balance and placed in an ultrasonic bath to dis- aggregate the finer particles. The samples were then wet-sieved, using a 230-mesh screen to separate the material finer than 0.0625 mm and then oven-dried. After drying, the samples were weighed to determine the weight percent of silt/clay relative to the sand fraction (table 1). The sand fraction was reduced by additional splitting to 10-g samples and analyzed in respect to grain-size distribution by a Rapid Sediment Analyzer (RSA). This apparatus uses the fall velocity of the sediment through a 1.33-m water column. The fall velocity "W" is calculated using Stokes Law, 2/ PI - P2 2 where p-j_ is the density of the sediment, p« is the density of the liquid, g is the acceleration of gravity, u is the dynamic viscosity of the liquid, and r is the radius of the sand particle. The fall times in seconds used for this study were values determined by Schlee (1966) and are contingent on the assumption that the sand consisted of quartz with a density of 2.65. The RSA was calibrated against sieves (Nelsen, 1974) and fall times were corrected accordingly. The RSA was electronically coupled with a Hewlett-Packard 9810 calculator to derive the mean, standard deviation, skewness, and kurtosis from the grain-size distribution for each sample (table 1). 1114 These values were developed from moment calculations , suggested by Krumbein and Petti John (1938), based on a sand fraction normalized to 100 percent. The silt/clay and coarse fractions were not included in the moment calculations to maintain a hydrodynamically similar sample. The grain-size distribution in quarter-phi units (negative log to the base two of the grain size in millimeters) and the corresponding metric equivalent are listed in table 2 . Median diameter maps have been prepared for each area from the grain-size analysis distributions (fig. 5 and 6). Ninety of the grab samples from area IB were coarse-sieved (> 2 mm) before the original splitting. The coarse fraction from the 1-kg sample was examined for content of detritus, clay pebbles, and fauna. The fauna was separated into respective classes of pelecypod, gastropod, or echinoid, with further separation to whole or fragmented specimens and to size of each. A relative -number percentage for each category appears as table 3. Heavy mineral analyses were run on 18 of the area IB samples. Because the heavier minerals are generally finer than 0.42 mm, the sand was first sieved to this size to increase the relative -weight percent- age of heavy minerals per sample (table 4). TABULAR RESULTS The bulk of this report consists of reduced data derived from the RSA in the form of grain-size distribution (tables 1 and 2), composition of the coarse fraction (table 3) , and the relative percentage of heavy 1115 BATHYMETRY IN FATHOMS 39°30* a^iO1 74°30' 74°20' 74°10' Figure 5. Isopleth map of mean grain size of area 1A in relation to the 5- and 10- fm. contours. 1116 39°10'N 73°55'W 73°45'W Figure 6. Isopleth map of mean grain size of area IB. The 20-fm. contour is shown. (From Stubblefield et al.3 1974.) 1117 minerals (table 4). Tables 1 and 2 are labeled in respect to areas 1A or IB, but tables 3 and 4 are confined to samples from area IB. In table 1, the columns reflect the following parameters of each sample. Column Parameter 1 Sample number 2 Latitude (North) 3 Longitude (West) 4 Water depth (in fathoms, 900 denotes a depth) 5 Weight percent of coarse fraction (> 2 6 Weight percent of sand fraction 7 Weight percent of fine fraction ( < 0.0 8 Mean grain size 9 Standard deviation 10 Sum of squares 11 Skewness 12 Kurtosis missed 0 mm) 0625 mm) Table 2 consists entirely of . grain-size distribution. Column Phi size Millimeter I 2- 6 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 sample number -0.99 through -0.75 -0.74 through -0.50 -0.49 through -0.25 -0.24 through 0.00 0.01 through 0.25 0.26 through 0.50 0.51 through 0.75 0.76 through 1.00 1.01 through 1.25 1.26 through 1.50 1.51 through 1.75 1.76 through 2.00 2.01 through 2.25 2.26 through 2.50 2.51 through 2.75 2.76 through 3.00 3.01 through 3.25 3.26 through 3.50 3.51 through 3.75 3.76 through 4.00 1.999 1.679 1.409 1.189 0.999 0.839 0.709 0.589 0.499 0.419 0.349 0.299 0.249 0.209 0.176 0.148 0.124 0.104 0.087 0.073 through through through through through through through through through through through through through through through through through through through through 1.680 1.410 1.190 1.000 0.840 0.710 0.590 0.500 0.420 0.350 0.300 0.250 0.210 0.177 0.149 0.125 0.105 0.088 0.074 0.0625 1118 Table 3 is a list of the 90 IB samples examined for coarse fraction ( > 2.00 mm) content. Each column reflects a point-count percentage rather than a weight percentage. Column Parameter (%) 1 Sample number 2 Detritus > 0.5 cm 3 Detritus < 0.5 cm 4 Clay pebbles > 0.5 cm 5 Clay pebbles < 0.5 cm 6 Echinoderms , whole , > 1 cm 7 Echinoderms, whole, < 1 cm 8 Echinoderms, fragmented, > 1 cm 9 Echinoderms , fragmented , < 1 cm 10 Pelecypods , whole, > 1 cm 11 Pelecypods, whole, < 1 cm 12 Pelecypods, fragmented, > 1 cm 13 Pelecypods, fragmented, < 1 cm 14 Gastropods, whole, > 1 cm 15 Gastropods, whole, < 1 cm 16 Gastropods, fragmented, > 1 cm 17 Gastropods, fragmented, < 1 cm Table 4 is the heavy mineral fractionation of the 19 samples from area IB. Column 1 is the sample number, and column 2 is the weight percentage of the heavies in the sand fraction, ranging from 0.42 to 0.0625 mm. The tabulated data are available to the reader on either digitized data cards or magnetic tape from the NOAA National Geophysical and Solar-Terrestrial Data Center, 3300 Whitehaven Street, N.W. , Washington, D.C. 20235. The request should be referenced by: Project - MESA, Ship - Venture, Year - 1972, for the data collected through the utilization of Loran; and by: Project - MESA, Ship - Peirce , Year - 1973, for those samples collected using Raydist navigational control. 1119 SUMMARY Two areas on the New Jersey Shelf were extensively bottom- sampled. The petrography of the collected samples is presented in the form of mean-grain diameter maps (fig. 5 and 6) and in tables 1 through 4. The tables include: geographic position of each sample; water depth; relative-weight percentage of coarse, sand, and fine fraction; four statistical moments plus sum of squares; grain-size distribution in quarter-phi intervals ; detritus , clay pebbles , and fauna within the coarse fraction; and heavy mineral analysis of selected samples. 1120 REFERENCES Duane, D.B., M.E. Field, E.P. Meisburger, D.J. P. Swift, and S.J. Williams (1972): Linear shcals on the Atlantic intercontinental shelf, Florida to Long Island, pp. 447-498; in: Swift, D.J. P. , D.B. Duane, and O.H. Pilkey, eds. , Shelf Sediment Transport: Process and Pattern ; Dowden, Hutchinson, and Ross, Inc., Stroudsburg, Pa. , 656 pp. Krumbein, W.C. , and F.J. Pettijohn (1938): Manual of Sedimentary Petrology 3 D. Apple ton -Century Co., New York, N.Y. , 549 pp. Nelsen, T.A. (1974): An automated rapid sediment analyzer (ARSA) , NOAA Tech. Memo., ERL AOML 21, 26 pp. Schlee, J. (1966): A modified Woods Hole Rapid Sediment Analyzer, Jour. Sedimentary Petrology 3 36(2) : 403-413. Shepard, F.P. , and R. Young (1961): Distinguishing between beach and dune sands, Jour. Sedimentary Petrology _, 31:196-214. Stubblefield, W.L. , J.W. Lavelle, T.F. McKinney, and D.J. P. Swift (1974) Sediment response to the present hydraulic regime on the Central New Jersey Shelf, Jour. Sedimentary Petrology (in press). Swift, D.J. P., D.B. Duane, and T.F. McKinney (1973): Ridge and swale topography of the Middle Atlantic Bight, North America: Secular response to the Holocene hydraulic regime, Mar. Geology } 15:227-247. Swift, D.J. P. , and P. Sears (1974): Estuarine and littoral patterns in the surficial sand sheet central and southern Atlantic Shelf of North America, in: Mien, G., ed. , Shelf and Estuarine Sedimen- tation: A Symposium^ Univ. of Bordeaux, Bordeaux, France (in press) . 1121 CN «; f s i. o <\ — r--f^f-f~-iniripir)- x^r^irif^ac\j3cra— ci<"3(var^cc>£cr300xfia:r^cf<'?<\cc\.r\aira.cca:a:oxcccr3 0 4* i ^lO[\]iooa(J,^a'OlPo^Drf^J'fl-,^HFf)CTO'C^^CJ(tlO^HGoca.I^Hf\JacolO/1Xfl/lo 0 oo ^c\i(\irMf\j(\i(\j(\jrO(V (\jf\.f\jc\jrvf\;<\j(\j »h . (\l C\J <\j «-t (\ <\. (\j O u cfes. (A f^rjvOoa^irij^^giria^r03-roojr)(V'03-(\,(\j3a:ir)r^i/>r^cfOro[^ir)ira,rocvjf^O'sC%£)i^3c\JLrr^3fOcc »0(NJt\jr0iOvD3-(\J -< <\l CD iT> in o c D C © ■■o to affa>0"asCTCTv3r--^r-'r-fo1CvDr-coKir-ir)3ca3^— itoin^jtMO'ccxi'ir^irxitrar-- OCToaaacro'00'oaar^>cCTa:f^air>cri-vC>cKiirr^ccacsocLr--'33crocoa'a.ccoooo 0"-HcooocKooocoor---OvC»03iaoocrt lf)KllOOC.<\i(MOCCCC.OCCinC\ia. 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Q. 0 c > o 4) CS QQ D 4) O^IMJvDBOBOlMOajrOvOOnjrt^fM _4> 1144 ftGPO 1974- 677-234/1216 REGION NO. 8 Continental Shelf Sedimentation Donald J. P. Swift INTRODUCTION In one of the first models of clastic sediments on continental shelves, Douglas Johnson (1919, p. 211) saw the shelf water column and the shelf floor as a system in dynamic equilibrium, in which the slope and grain size of the sedimentary substrate at each point controls, and is controlled by, the flux of wave energy into the bottom. The resulting surface is concave upward, steeper toward the shoreface. Grain size decreased with depth and distance sea- ward, and as a direct function of the diminishing input of wave energy into the sea floor. The model derived its sediment from coastal erosion rather than from river input. Despite its qualitative expres- sion and limited applicability, the model was in advance of its time in its dynamical, systems analy- sis approach. Shepard (1932) was the first to challenge it, noting that most shelves were veneered with a complex mosaic of sediment types rather than a simple seaward-fining sheet. He suggested that these patches were deposited during Pleistocene low stands of the sea rather than during recent time. Emery (1952, 1968) classified shelf sediments on a genetic basis, as authigenic (glauconite or phosphorite), organic (foraminifera, shells), resid- ual (weathered from underlying rock), relict (rem- nant from a different earlier environment such as a now submerged beach or dune), and detrital, which includes material presently being supplied by riv- ers, coastal erosion, and aeolian or glacial activity. On most shelves a thin nearshore band of modern detrital sediment is supposed to give way seaward to a relict sand sheet veneering the shelf surface. A third model for shelf sedimentation incorpo- rates elements of both the Johnson and Emery models. It views the shelf surface as a dynamic system in a state of equilibrium with a set of process variables, but the rate of sea-level change is one of these variables and thus includes the effects of post-Pleistocene sea-level rise. The model may be referred to as a transgression-regression model, since it is generally expressed in these terms, or as a coastal model, since it focuses on the behavior of this dynamic zone (Grabau, 1913; Curray, 1964; Swift et al.. 1972b). The respective insights of these various models are by no means mutually exclusive. The process variables of the transgressive-regressive model are surely the dominant controls of the shelf sedimen- tary regime, and also the controls that shape the coastal boundary, a term used here to describe both the configuration of the inner shelf surface and the intracoastal zone of lagoons and estuaries. The rate of sediment bypassing through the coastal boundary and the character of sediment bypassed are controlled by the equilibrium values attained by the process variables within the coastal boundary (Johnson model); hence this coastal equi- librium system itself modifies the sedimentary re- gime of the shelf and determines the petrographic types of Emery (1968) and stratigraphies of Curray (1964). The shelf may be viewed as a dynamic system that is controlled by sediment flux through the coastal boundary, and also by the flux of energy through the water column into the substrate. This report will describe some characteristic patterns of shelf process and response. No text exists at this time which adequately deals with this material; however, Neuman and Pierson (1966) provide a lucid general treatment of physical oceanography. The mechanics of sediment transport have been ably summarized by Allen (1970a); see Bagnold (1963, 1966), Sternberg (1972), and Ludwick (1974) for advanced treatments. COASTAL BOUNDARY There are two basic categories of "valve" which regulate the passage of sediment from the continental sediment transport system into the do- main of the continental shelf. The shoreface, during periods of coastal retreat, may erode and release sediment. This is an indirect process; the sediment released must first undergo storage as floodplain, lagoonal, or estuarine deposits, or be derived from an earlier cycle of sedimentation. River-mouth by- passing is more direct than shoreface bypassing, but sediment must still undergo storage. Sand is stored in the throat of the river mouth and fines are stored in marginal marshes and mud flats until the period of maximum river discharge, when the salt wedge moves to the shoal crest and stored sediment is bypassed to the shoreface of the shoal front. It may undergo a second period of storage on the shoreface and inner shelf until the period of maxi- mum storm energy (Drake et al.. 1972). The mode of operation of these valves is depen- dent on basic parameters of coastal sedimentation: the absolute value of river discharge per unit length of coast, the ratio of salt water to fresh water discharge in river mouths, the wave climate, and finally the rate and sense of coastal translation as a 117 1145 118 Continental Margins function of sediment input, sea-level displacement, and energy input. The fluvial discharge per unit length of coast determines the spacing of river mouths and is the fundamental determinant of the relative roles of shoreface versus river-mouth by- passing. An intense tidal regime increases the effi- ciency of river-mouth bypassing, while an intense wave climate increases the efficiency of shoreface bypassing. The rate and sense of coastal translation also strongly affects the relative roles of river mouth and shoreface bypassing. Rapid transgression results in disequilibrium estuaries which become sediment sinks, and shoreface and downdrift bypassing must dominate. The resulting sand sheet consists of a transient veneer of surf fallout on the upper shore- face and the residual sand sheet of the lower shoreface and adjacent shelf. These correspond to Emery's (1968) nearshore modern sand and shelf relict sand, respectively. Both are relic* in the sense that they have been eroded from a local, pre-recent substrate, and both are modern, in the sense that they have been redeposited under the present hy- draulic regime. They are, in fact, palimpsest sedi- ments (Swift et al., 1971b), since they have petro- graphic attributes resulting from both the present and the earlier depositional environment. The term "relict" is best reserved for those specific textural attributes reflecting the earlier regime. Perhaps the most effective term for the provenance of these materials is autochthonous, and a shelf sedimentary regime characterized by rapid transgression and shoreface and downdrift bypassing will be hence- forth described as a regime of autochthonous shelf sedimentation. With a slower rate of translation, estuaries can equilibrate to their tidal prisms and river mouth, and shoreface bypassing becomes a significant source of sediment. More subtle, but equally impor- tant, is the effect of a slow transgression on the grain size of bypassed sediment. With a slower rate of shoreline translation, the intracoastal zone of estuaries and lagoons can aggrade nearly to mean sea level. The resulting surface of salt marshes (or in low latitudes, mangrove swamps) threaded by high-energy channels tends to serve as a low-pass or bandpass filter. Migrating channels preferen- tially select coarse materials for permanent burial in their axes. The surfaces of the tidal interfluves receive the finest materials for prolonged storage or permanent burial. However, fine sands and silts deposited as overbank levees tend to be reentrained by the migrating channels, hence have the highest probability of being bypassed to the shelf surface. This material is sufficiently fine to travel in suspen- sion for long distances. As the sense of coastal translation passes through stillstand to progradation, the shoreface becomes a sink rather than a mechanism for by- passing. Distributary mouths must further partition their prefiltered load, between sand sufficiently coarse to be captured by the littoral drift and buried on the shoreface and sand fine enough to escape in suspension in the ebb tidal jet and be entrained into the shelf dispersal system. The shoreface is now a total sediment trap, and bypassing is entirely through river mouths. Shelves undergoing slow transgression or re- gression thus experience a contrasting regime of alJochthonous shelf sedimentation characterized by significant river-mouth bypassing. In this regime there is a massive influx of river sediment filtered by passage through the coastal zone. Sheets of mobile fine sand and mud stretch from the coast toward the shelf edge. Shorefaces are broad and gentle and merge imperceptibly with a shallow inner shelf. The allochthonous regimes, which build the broad constructional shelves, and the autochthon- ous regimes which periodically invade them, will be reviewed by means of a few representative ex- amples whose dynamics are relatively well known. CENTRAL ATLANTIC SHELF OF NORTH AMERICA: STORM-DOMINATED AUTOCHTHONOUS REGIME Hydraulic Climate. The central Atlantic Shelf of North America is a storm-dominated shelf; midtide surface velocities are generally less than 20 cm/sec, except in the vicinity of tidal inlets and estuary mouths. (Redfield, 1956). As such, it experiences long periods of quiescence, mainly during the summer. At this time the shelf water mass is den- sity-stratified and undergoes a slow, southerly, coast-parallel drift under the impetus of prevailing fair-weather winds and freshwater runoff (Harri- son et al., 1967). The latter factor results in a nearshore elevation of the sea surface sufficient to induce a coast parallel, geostrophic flow of water, with an offshore surface component and a landward bottom component (Bumpus, 1973). This southward flow becomes entrained by the north-trending Gulf Stream at Cape Hatteras. The central Atlantic Shelf is in the lee of the continent with respect to the prevailing planetary winds. Summer swells are far traveled and attenu- ated and are damped further at the shelf edge. Near-bottom wave surge on the shelf is occasionally able to ripple the bottom (McClennen, 1973) but becomes a significant agent of sediment transport only on the shoreface, in 15 m or less of water. Farther seaward, the resultant fair-weather veloc- ity field of wave surge, wind drift, and thermohaline components is competent only to transport sus- pended fine sediments. However, summer concen- trations of suspended sediment are low, usually less than 1 mg/liter except near estuary mouths and tidal inlets (Manheim et al., 1970), since the thresh- old velocities needed to suspend such materials are generally not exceeded. By November the water column has cooled sufficiently to lose thermal stratification, and the increased frequency of storms has broken down 1146 cfhelf Sedimentation 119 SUI'ACI WINO OIIVIN CUIIINI • OTTO** WIND OftlVEN CUIIEHI SUtFACE WAVI DI1VCN CUItENT ZONt OF WIND-OHVEN SMOAiiNG DOWNWELUNO WAVES COASTAL JET ng 1. Hypothetical model of the coastal boundary of the storm flow field during a period of onshore wind. Convergence of wind driven current with shoreline results in downwelling coastal jet. salinity stratification. During such storms, wind stress on the sea surface drives Langmuir circula- tion in the mixed layer (Gordon and Gerard, in press). The stratified lower layer is eroded by this mechanism, so the mixed layer grows at its expense, until the stratified layer is entirely consumed and the rapidly flowing mixed layer is in contact with the sea floor. The storm flow field of the central Atlantic Shelf is poorly understood. Storms tend to move northeastward up the shelf, parallel to the coast. As the storm approaches, winds rotate into the north- east and intensify as they do so. resulting in appre- ciable setup of water against the coast. Nearshore currents respond quickly to wind stress in this northward-migrating water bulge (Swift et al., 1973; B. Butman. M.I.T., unpublished data). The early work of Ekman (1905, in Neumann and Pier- son, 1966, p. 203) suggests that under such circum- stances streamlines of coastal flow should converge with each other as they converge with the coast, resulting in a coastal jet; the pressure head due to wind set up may be relieved by downwelling and obliquely seaward bottom flow as well as by down- coast flow (Fig. 1). Current meter records indicate that storm flows are adequate to mobilize at least the inner shelf floor (Fig. 2). Values for sediment transport presented in Figure 2 are probably underestimated, since the lubricating effect of bottom wave surge was not taken into account. Wave surge is most intense during storms when unidirectional flow is also at a maximum. Wave surge generates steep sided ripples that increase the shear stress required to entrain sand (Bagnold, 1963), but field observa- tions indicate that the sand of ripple fields is size- sorted with respect to the hydraulic microenviron- ment, with coarse sand in crests and finer sand in troughs, so that the whole surface is activated simultaneously as peak surge velocity is approached (Cook and Gorsline, 1972). Coupling between bound- ary surge and ripple is such that a burst of susr pended sand is injected from the ripple crests into the boundary flow (Kennedy and Locher, 1972). In general, the effect of wave surge on the storm flow field is probably to depress the threshold values for sediment entrainment by the mean flow. Origin of the Surficial Sand Sheet. The surficial sand sheet of the central and southern Atlantic Shelf was produced by the erosional retreat of the shoreface during the Holocene transgression, and its sediment textures and morphology faithfully re- ClASJ X VOIUMI ■OUNOAIliS EXCEEOENCE TIANSPOIT (fHI| («3/„/T) COAISE SAND 0-1 6.0 1.4 SIZE CLASS |MtOiUM SAND ^EIMI SAND 1VEIT FINE SAND 1-2 3-3 3-4 11.0 IS I iro • 0 7.5 S.I 30 r 10 ® CUItENT METEI STATION • STATIONS 1 NET TIANSPOIT DIIECTION )k^y^K^J\J^^^J^^ 12 16 OATS 20 24 21 Fig. 2. Sediment transport during the month of November, 1972, in an inner shelf ridge field. False Cape Virginia. Estimates based on Shield's threshold criterion, a drag coefficient of 3 X 10~3 and Laursen's (1958) total load equation. Values expressed aa m3 of quartz per meter transverse to transport direction for time elapsed. 1147 120 Continental Margins Fig. 3. Morphologic elements of the Middle Atlantic Bight. From Swift, in press. MODERN ESTUARY MOUTH SHOAL, TIDAL CHANNELS PAIREO FLOOO CHANNEL RETREAT TRACK. ESTUARINE SHOAL-RETREAT MASSIF — 40M SCARP TRANSGRESSED CUSPATE DELTA; (CAPE SHOAL- RETREAT MASSIF) — 60M SCARP fleet patterns of littoral sedimentation during this period. Zones of tidal scour at estuary mouths, and convergences in the littoral drift system and off cuspate forelands, have left records of their retreat as subdued, shelf transverse lows and highs, much as objects in a photograph leave streaks if the camera has moved while the picture is taken (Fig. 3). The sand sheet thus formed has continued to respond to the storm hydraulic regime, most notably by the overprinting of the relict nearshore topo- graphic pattern by a ridge-and-swale topography that may in some respects be analogous with the fields of longitudinal dunes characteristic of sub- aerial sand seas (Wilson, 1972). Relict Components of the Depositional Fabric. Uniformitarian principles may be readily applied to interpretation of relict morphologic, stratigraphic, and textural components in the depositional fabric of the surficial sand sheet. These components may be explained in terms of the modern littoral regime of the adjacent coast. The Middle Atlantic Bight is Fig. 4. Down-drift bypassing at the mouth of an erosional estuary (Delaware Bay. North American Atlantic Shelf). Southward littoral drift of New Jersey coastal compartment is injected into reversing tidal stream of mouth of Chesapeake Bay. The resulting shoal is stabilized as a system of interdigitating ebb and flood channels, north of the main couplet of mutually evasive ebb and flood channels. The shelf valley complex seaward of the bay mouth is the retreat path of the bay mouth sedimentary regime through Holocene time. Retreat of the main flood channel has excavated the Dela- ware Shelf Valley: retreat of the baymouth shoal has left a seaward trending shoal-retreat massif on the shelf valley's north flank; an example of down-drift bypassing. From Swift, 1973. 1148 ohelf Sedimentation characterized by long, straight coast compart- ments, alternating with the mouths of master river systems that have been drowned to form large erosional estuaries. Relatively little sediment passes down these rivers from the temperate, glaciated hinterland, and the estuaries are able to efficiently trap it out and to trap out the littoral drift of the adjacent coastal compartments as estuary mouth shoals (Meade, 1969). In the Middle Atlantic Bight, a large-scale depositional fabric consists of an alternation of shelf-transverse thickenings in the sand sheet (Swift and Sears, in press). These shelf valley complexes tend to consist of a partially filled river-cut valley paired with a shoal-retreat massif. The fill .of the subaerial valley may have a narrow channel incised into it. Thinner sand blankets, the product of ero- sional shoreface retreat, occur on the plateau-like interfluves. Shelf valley complexes cannot always be traced to their littoral generating zone as a consequence of changes in the littoral sedimentation pattern attendant on the late Holocene reduction in the rate of sea-level rise (Milliman and Emery, 121 1968). The narrow Delaware Shelf Valley, however, can be traced directly into the flood-dominated channel that adjoins, in an echelon fashion, the ebb-dominated channel of the inner estuary mouth (Fig. 4). Such mutually evasive ebb-flood channel couplets are characteristic of estuary mouths (Lud- wick, 1973) and the Delaware Shelf Valley is, in fact, the retreat path of the flood-dominated mem- ber of the pair. It only approximately follows the trend of the buried river-cut valley beneath it (R. Sheridan, personal communication). The north-rim high is similarly the retreat path of the north-side estuary mouth shoal that serves as a depositional focus for the New Jersey coastal compartment; this shoal-retreat massif constitutes a major zone of downdrift bypassing. Cores through the similar Albermarle Massif reveal a nuclear estuarine facies resting on a late Wisconsinan substrate and man- tled by younger shelf sands (Fig. 5). The intervening plateau-like massifs are ve- neered with 0-10 m of surficial sand. On long stretches of the coast, this material accumulates uniformly at the foot of the shoreface. Elsewhere, KILOMETERS 15.5- 280 405-1 SURFICIAL SAND ESTUARY MOUTH SAND _J PLEISTOCENE SUBSTRATE VERTICAL EXAGGERATION 20O« I* 2* 3* 4* Fig. 5. Section through Piatt Shoals, an estuarine shoal-retreat massif on the south flank of the Albermarle shelf valley complex. Note nucleus of estuary mouth deposits. Depositional environment was equivalent to downTCurrent side of estuary mouth. Fig. 8. From Swift and Sears, in press. 1149 122 Continental Margins rhythmic perturbations in the form of shoreface- connected sand ridges occur on the shoreface, in response to perturbations in the storm flow field of downwelling, southerly trending shoreface cur- Fig. 6. Shoreface-connected ridge field of the Delmarva Coast. Ridges are nourished by storm current erosion of the shoreface. Ridges are migrating southeast (downcoast and offshore), while extending crest lines to maintain contact with the shoreface. As trough grows through headward and axial erosion, storm currents in trough become more in- tense, and eventually cut saddle. Perturbation of sea floor* continued as new ridge downcoast, resulting in stepwise crest line (compare lower diagram with crestlines in map}. rents, and the nearly symmetrical surge of high storm waves (Figs. 1 and 6; Swift et al., 1972a; Duane et al., 1972). Each ridge is nourished by storm erosion of the up-current shoreface. Head- ward and axial erosion of the troughs during region- al retreat of the shoreface results in periodic isola- tion of ridge segments on the deepening inner shelf floor, an important form of small-scale downdrift bypassing. The resulting stratum is a ridged sand sheet whose structures and textures reflect the course of the Holocene transgression. This pattern of shelf valley complex alternating with shoreface retreat blanket, characteristic of the Middle Atlantic Bight, is replaced by alternative patterns farther north and south (Swift and Sears, in press). To the north, the shelves have been glaciated and relief is greater. Here shelf highs are cuestas and similar erosional forms; river-cut val- leys are only partially filled with estuarine deposits. Glacial basins in the Gulf of Maine and Scotian Shelf are presently accumulating mud. To the south, off the Carolina salient, cape shoal-retreat massifs extend seaward from the lit- toral drift convergences off cuspate forelands. Off South Carolina, the massifs off small cuspate fore- lands merge as a cape shoal-retreat blanket. The closely spaced estuaries of the South Atlantic Bight may have similarly generated an estuarine shoal- retreat blanket. The smooth outer shelf from Cape Cod to Florida appears to be a zone of shelf-edge deltas. Equilibrium Components of the Deposit ional Fabric. On the central Atlantic Shelf, then, the morphologic and stratigraphic framework of the shelf sand sheet is the consequence of erosional shoreface retreat and shoreface and downdrift bypassing. However, the sheet is clearly in a state of continuing response to the storm-dominated Holocene hydraulic regime. Inherited sand ridges continue to be maintained; bare Pleistocene substrate continues to be exposed in adjacent troughs. New ridges are constructed. Tide-built ridges on the retreating estuary mouth shoals may rotate from their initial coast-normal orientation to a more nearly coast-parallel orienta- tion as the shoreline retreats, in response to weak- ening of the influence of estuary mouth tidal streams, and the increasing importance of coast- parallel storm currents. Where the older ridges are especially wide or deep, a new, smaller-scale ridge pattern may be imprinted obliquely across the old. Shelf-floor ridges shift landward or seaward and extend southward. A regional redistribution of sedi- ment occurs, whereby fine and very fine sand is swept by storm flow out of ridge fields and out of the troughs incised into shoal-retreat massifs, and into zones of flow deceleration and expansion, in the shelf valleys beyond the massifs, and in downcoast reentrants (Fig. 7). Sediment fractionation occurs on a smaller scale within the ridge topography (Stubblefield et al., in press). Crest al sands are uniformly medium 1150 >• TIDAL CURRENTS Fig. 7. Above: Bathymetry of the Delmarva Inner Shelf, from Uchupi. 1970. Center: Distribution of sediment, from Hathaway. 1971 and Nichols, 1972. Below: Inferred direction of sediment transport. to fine grained; their relatively high percentages of finer interstitial sand suggest deposition by high- intensity flow (rheologic flow; Moss, 1972). Trough sands are highly differentiated. Fine and very fine sands in troughs may have settled from graded suspension. Coarse sands exposed in trough axes have the interstitial fine populations and very coarse laminae (traction clogs), indicating high-in- tensity flow (Moss, 1972). All three sand types occur on flanks, but fine to very fine sands are dominant. In some troughs, sidescan sonar records reveal a dark axial band, interpreted as an elongate ero- sional window in the Holocene sand sheet, exposing a thin gravelly or shelly lag, resting on finer lagoon- al deposits (McKinney, in press). Paired bands indicate that trough erosion has cut through a shelly bed in the pre-recent substrate. Sidescan records also reveal small-scale sand ribbon-like features in troughs, which are interpreted as responses to small-scale helical flow in the bottom boundary layer of the storm flow field. The surface of the Middle Atlantic Bight of the North American Shelf appears to be in a state of equilibrium with the hydraulic regime, in terms of texture and morphology. Large-scale topographic features and textural patterns created during shoreface retreat have not been completely obliter- ated, however, so the equilibrium is imperfect. The equilibrium is a dynamic one in the sense that there is throughput of sediment across a surface of rela- tively stable morphology and texture. In budgetary terms, this system is also in a state of near dynamic equilibrium. A finite amount of sediment is being introduced into the shelf sur- 1151 124 Continental Margins face by shoreface retreat and is flowing intermit- tently southward in response to storms (Swift et al., 1972b). The moving material must ultimately attain permanent storage on the shelf as current-adjusted deposits or be swept off the shelf edge. During Pleistocene low stands of the sea, the southward sand flux of the Middle Atlantic Bight was appar- ently tapped by the Hatteras canyon system, as the Hatteras abyssal plain is floored by material of this source (Horn et al., 1971). During the present high stand, however, the Hatteras shelf edge is capped by biogenic ooze deposited from the Gulf Stream, and the sand stream is instead aggrading the shelf north of Cape Hatteras. SHELF AROUND THE BRITISH ISLES: A TH)E DOMINATED AUTOCHTHONOUS REGIME Hydraulic Climate of Tidal Shelves. As the oceanic tide propagates onto the continental shelf, its maximum current velocity, Umax, is increased since the maximum orbital velocity of a shallow- water wave varies inversely with depth. Energy loss into the sea floor is rapid, however, and the wave will be rapidly damped. Thus the maximum tidal velocity on the shelf, Umax, is a function of the ratio of distance from shore to depth, Xh. as well as the amplitude of the tidal wave, C, and its period, T (Fleming and Revelle, 1939) _ 2 7rCX umax — TH The tidal wave may propagate onto the shelf as a progressive wave. More commonly, sufficient en- ergy is reflected from the shoreline so that the shelf wave is a standing oscillation that cooscillates with the oceanic tide. Current velocities are 90° out of phase with water level, so maximum velocities oc- cur at midtide, minimum velocities at high and low tide. As a consequence of the Coriolis effect, shelf tides are rotary, with the flood (rising, landward- flowing) tide veering to the right in the Northern Hemisphere, and the ebb (falling, seaward-flowing) tide veering to the left. On embayed shelf sectors, bounded laterally as well as on the back by land masses, an amphidromic system results. In the North Sea, the basic standing wave is modified in this fashion into several progressive edge waves that sweep counter-clockwise around the basin (Fig. 8). Another type of rotary tidal stream pattern may be set up by the effect of the rotation of the earth on a progressive tidal wave in a fairly narrow channel, where compensation is achieved by the development of transverse streams rather than by the setting up of subsidiary gradi- ents. Such streams will rotate clockwise in the Northern Hemisphere, as in the English Channel. The most intensive sediment streams are asso- ciated with the progressive edge waves that sweep around the margins of the amphidromic systems of marginal tidal seas. Amplitude of these edge waves increases toward shore, and so do their shallow- water distortions, resulting in net coast-parallel sediment transport. However, owing to the settling- lag phenomenon (Postma, 1967), transport will tend to have an onshore or offshore component (Stride, 1973). In addition to inherent velocity and discharge asymmetries, transport inequalities in tidal seas may also be due to preferred patterns of wind-drift currents and storm surge. Storm surges moving as solitary edge waves pass along the western side of the North Sea, for instance, and markedly amplify the flood currents on that side (Ishiguro, 1966). Intensified wave surge associated with storms also greatly amplifies the transporting power of tidal currents (Johnson and Stride, 1969). ".^S Of EO^AL MEAN *t*s"». *tS HOUW5 AfTTR THE MOO** TftAhSi .CH TMC MtfflO'AN OF ^".lV*K* TIOAL WAVES VERTICAL TIOAL RANGE AVERAGE MAXIMUM TIOAL CURRENT Fig. 8. Tidal regime of the North Sea. From Houbolt. 1968. AVERAGE SURFACE CURRENTS 1152 Shelf Sedimentation 125 Sediment Transport Around the British Isles. The "tide-swept" shelf around the British Isles (Stride, 1963) is subjected to an autochthonous sedimentary regime. The Thames. Severn, and Humber debouch in estuaries; the Rhine "delta" consists at present of estuarine distributaries. Such Fig. 9. Tide-maintained ridge topography on the inner Anglian Shelf. Shoreface-connected ridges separate ebb- and flood- dominated channels. Ridges tend to migrate southward with time, and to detach from retreating shoreface. Ridges are nourished at the expense of shoreface, hence constitute cases of down-drift bypassing. Offshore ridges are probably being nourished at expense of nearshore ridges: if so, sand is moving seaward more rapidly than are the ridge forms, and dynamic bypassing is occurring also. From Robinson, 1966. dynamic bypassing as occurs in these estuaries is not sufficient to prevent the erosional retreat of the adjacent coasts, including the Dutch coast down- drift of the Rhine Delta (Van Straaten, 1965). The formation of the surficial sand sheet by tidal erosion of the shoreface and reconstitution of its materials under the tidal hydraulic regime are analyzed by Belderson and Stride (1966). Tide-induced erosional retreat of the Anglian coast is accomplished by the growth, migration, and detachment of shoreface- connected ridges similar in some respects to those of the Middle Atlantic Bight. However, they are main- tained not primarily by storm flow but by residual tidal discharge that has a flood value on the inner flank and an ebb value on the outer flank (Fig. 9; Robinson, 1966). Storage and periodic detachment of these shoreface sand masses appears to have created a shoal retreat massif of tide-maintained sand ridges that extends for 200 km out into the North Sea (Fig. 10; Caston, 1972). u Fig. 10. Tidal ridge field of the Anglian Shelf. Ridges are confined to map area. These features appear to constitute a shoal-retreat massif, marking the retreat path of the near- shore tidal regime of the Anglian coast. From Caston. 1968. 1153 126 Continental Margins In general, however, such stabilized morpho- logic traces of the retreat of nearshore sedimenta- tion zones are less common on the British shelves, since the debris sheet generated by shoreface re- treat has responded to the more intense, tide-domi- nated hydraulic climate with a much greater degree of mobility. The pattern of transport is surprisingly well organized, with sand streams diverging from beneath tide-induced "bedload partings" and flow- ing down the gradient of maximum tidal current velocities until either the shelf edge or a zone of "bed-load convergence" and sediment accumula- tion is reached (Stride, 1963; Kenyon and Stride, 1970; Belderson et al., 1970). Each stream tends to consist of a sequence of more or less well-defined zones of characteristic Fig. 11. Generalized sand transport paths around the British Isles and France, based on the velocity asymmetry of the tidal ellipse and the orientation and asymmetry of bedforms. From Kenyon and Stride, 1970. Fig. 12. Four main types of sand ribbons and the typical near-surface current veolcities at which they occur. From Kenyon, 1970. bottom morphology and sediment texture (Fig. 11). Streams may begin in high-velocity zones [midtide surface velocities in excess of 3 knots (150 cm/sec)]. Here rocky floors are locally veneered with thin (centimeters thick) lag deposits of gravel and shell. Where slightly thicker, the gravel may display "lon- gitudinal furrows" parallel to the tidal current, a bedform possibly related to sand ribbons (Stride et al., 1972). Between approximately 2.5 and 3.0 knots (125- 150 cm/sec) sand ribbons are the dominant bed form (Kenyon, 1970). These features are up to 15 km long and 200 m wide and usually less than 1 m deep. Their materials are in transit over a lag deposit of shell and gravel. Kenyon has distinguished four basic patterns which seem to correlate with maxi- mum tidal current velocity and with the availability of sand (Fig. 12). Farther down the velocity gradient, where mid- tide surface velocities range from 1 to 2 knots (50-100 cm/sec), sand waves are the dominant bed form. Where the gradient of decreasing tidal veloc- ity is steep, or transport convergence occurs, this may be the sector of maximum deposition on the transport path. Over 20 m of sediment has accumu- lated at the shelf-edge convergence of the Celtic Sea, although it is not certain that this sediment pile is entirely a response to modern conditions. The Hook of Holland sand wave field off the Dutch coast is one of the largest (15,000 km2) and the best known (McCave, 1971). The sand body is anomalous in that it sits astride a bed-load parting; the sand patch as a whole may be a Pleistocene delta or other relict feature. Sand waves with megaripples on their backs grow to equilibrium heights of 7 m with wavelengths of 200-500 m in water deeper than 18 m; in shoaler water, wave surge inhibits or supresses them. Elongate tidal ellipses favor transverse sand wave formation, and 1154 Shelf Sedimentation 127 Fig. 13. Niger Delta and relation of river discharge to wave oower over the yearly cycle. Histograms are wave power over the yearly cycle at the 30 foot contour (A) and nearshore (B). From Wright and Coleman, 1973. the sand waves tend to be destroyed by midtide cross-flow when the ellipse is less symmetrical. Under the latter condition, linear sand ridges may be the preferred bedform, as midtide cross flow would tend to nourish rather than degrade them (Smith, 1969). The triangular sand wave field is limited by a lack of sand on the northwest, by shoaling of the bottom and increasing wave surge on the coast to the south, and by fining of sand to the point that suspensive transport is dominant to the north (McCave, 1971). Farther down the velocity gradient, beyond the zones of obvious sand transport, there are sheets of fine sand and muddy fine sand and in local basins, mud. They lack bed forms other than ripples and appear to be the product of primarily suspensive transport (McCave, 1971) of material that, has out- run the bed-load stream. These deposits may be as thick as 10 m (Belderson and others, 1966), but where they do not continue into mud, they break up into irregular, current-parallel or current-trans- verse patches of fine sand less a 2 m thick, resting on the gravelly substrate. The complex pattern and mobile character of the shelf floor around the British Isles have led British workers to reject the relict model for ihe shelf sediments. They note that it correctly draws attention to the autochthonous origin of the sedi- ment but that it fails to allow for its subsequent dynamic evaluation. They propose instead a dy- namic classification: 1. Lower sea level and transgressive deposits, patchy in exposure but probably more or less con- tinuous beneath later material; largely the equiva- lent of a blanket (basal) conglomerate. 2. Material moving as bed load (over the coars- er basal deposits) mainly well-sorted sand and in places first-cycle calcareous sand. 3. Present sea-level deposits (category 2 sedi- ment having come to permanent rest), consisting of large sheets to small patches, which range from gravel and shell gravel to sand and calcareous sands, muddy sands, and muds. The implication is that of a shelf surface in a state of equilibrium with its tidal regime. The ad- justment appears to be more effective than in the 1155 128 Continental Margins case of the North American Atlantic Shelf in that there is less preservation of nearshore depositional patterns. As a consequence of the intensity of the hydraulic climate, there is less on shelf storage (category 3) and more material in transit. NIGER SHELF: STORM DOMINATED AUTOCHTHONOUS REGIME General. A very different regime of shelf sedi- mentation, and probably one more representative of the allochthonous regimes that have built the broad constructional shelves of continental margins, is that of the Niger delta, as described by Allen (1964). The hydraulic climate of the Niger Shelf is probably most nearly analogous to that of the Central Atlantic Shelf, in that storm flow is more significant than tidal flow in driving shelf sedimentation. The shelf is dominated by the great arcuate Niger delta (Fig. 13), a concentric assemblage of terrestrial and transitional depositional environments that filter and modify the sediment load of the Niger River, before bypassing it to the Niger Shelf. Such a delta is by no means a prerequisite for allochthonous sedimentation, although the correlation between major river mouths and allochthonous sedimenta- tion is probably higher in the present period of relatively rapid transgression than during the slow transgressions of the past. Differential Bypassing in the Deltaic Environments. The Niger-Benue river system delivers about 0.9 X 106 m3 of bed-load sediment and about 16 X 106 m3 of suspended sediment (Allen, 1965) to its delta each year. During peak discharge from September to May, average flow velocities range from 50 to 135 cm/sec. and gravel as well as sand are in violent transport. During low stages, flow velocities de- crease to 37 to 82 cm/sec, enough to transport sand and silt. In the higher part of the floodplain, the Niger is braided; in the remainder the Niger shows large meanders (Fig. 14). During high stages, levees are overtopped, crevasses develop, and bottom Orgomtm burrow* ond tunnflf Root* ond fooiiat* ClOyty silt Ond sillv City !(C) - coortt gf (M) - mtdiurfi gr IF] • tint 0» (VFI- >tr) tint g< Fig. 14. Schematic illustration of the depositional environments and sedimentary facies of the Niger Delta and Niger Shelf. From Allen, 1970. 1156 Shelf Sedimentation 129 lands are flooded. Gravel and coarse sand are deposited as a substratum of braid bars and mean- der point bars, respectively, and are veneered with a top stratum of overbank clays. Silt undergoes temporary deposition in levees in the lower flood- plain, but these tend to be undermined, so that their deposits reenter the transport system. Thus the floodplain environment serves as a skewed bandpass filter, with preferential bypassing of the medium grades, entrapment of some fines over bank, and much coarse material deposited in channel axes. This process continues through the tidal swamp environment, where the entrapment of fines dominates. Reversing tidal flows generate vel- ocities of 40-180 cm/sec in tidal creeks, enough to move sand and gravel. Entrapment of fines over- bank in the mangrove swamps is enhanced by the phenomena of slack high water and the prolonged period of reduced velocity associated with it. Fines then deposited begin to compact, and require great- er velocities to erode them than served to permit their deposition. Major channels, which pass through the inter- tidal environment to the sea, must store their coars- er sediment during low-water stages at the foot of the salt wedge, where the landward-inclined sur- face of zero net motion intersects the channel floor. During high-water stages, stored bottom sediment must be rhythmically flushed out of the estuary mouth by the tidal cycle. Sand coarser than the effective suspension threshold of 230 microns (Bag- nold, 1966) will be deposited on the arcuate estuary mouth shoals (Oertel and Howard, 1972), where, after a prolonged period of residence in the sand circulation cells of the shoal, it leaks into the downcoast littoral drift system. Finer sand is en- trained into suspension by large-scale top-to-bottom turbulence in the high-velocity estuary throat (Swift and Pirie, 1970, p. 75) and will be swept seaward with the ebb tidal jet, to rain out on the inner shelf (Todd, 1968), where it is accessible to distribution by the hydraulic regime. The shoreface constitutes a second major zone of storage, since the periods of peak river discharge and peak wave power do not coincide on the Niger shelf (Fig. 13). Such poor coupling is a significant factor in coastal progradation, since the resulting sediment prism has a chance to consolidate prior to erosion. Transport on Alloc hthonous Shelves. Drake et al. (1972) have presented a detailed case history of the seaward dispersal of such a nearshore prism of stored sediment (Fig. 15). In January and February 1969, southern California experienced two intense rainstorms, which resulted in a record flood dis- charge. The freshly eroded sediment was a' distinc- tive red-brown in contrast to the drab hue of the reduced shelf sediments. The flood layer could therefore be repeatedly cored and isopached and its shifting center of mass traced seaward through time. 34°20 34°10 34° 20 34°10 34-20 34<>10 ^^ 119° 50' WIO1 °f" o»« 0?*= w J © ■■'&& Fig. 15. Upper 3 diagrams: thickness of flood sediment (cm) on the Santa Barbara-Oxnard Shelf in March-April. 1969; May-August, 1969; and February-June, 1970, based on cores. Lowest diagram: East-west cross section showing vertical distribution of light attenuating substances over Santa Barbara-Oxnard Shelf. For clarity, the bottom 20 m of the water column is not contoured, but the percent trans- mission value at the bottom is noted. From Drake and Kolpack, 1972. U.S. Geological Survey stream records show that 33-45 X 106 metric tons of suspended silt and clay and 12-20 X 106 metric tons of suspended sand were introduced by the Santa Clara and Ventura rivers. By the end of April 1969, more than 70% of this material was still on the shelf in the form of a submarine sand shoal extending 7 km seaward, and a westward thinning and fining blanket of fine sand, silt, and clay existed seaward of that (Fig. 15A). By the end of the summer of 1969, the layer extended farther seaward, had thinned by 20%, and had developed a secondary lobe beneath the Anacapa current to the south (Fig. 15B). Eighteen months after the floods, the surface layer was still 1157 130 Continental Margins readily detectable. Considerable bioturbation, scour, and redistribution had occurred south of Ventura, but the deposit was more stable to the north (Fig. 15C). A concurrent Study of suspended sediment dis- tribution in the water column revealed the pattern of sediment transport (Fig. 15D). Vertical trans- parency profiles, after 4 days of flooding, showed that most of the suspended matter was contained in the brackish surface layer, 10-20 m thick. Profiles in April and May revealed a layer 15 m thick, with concentrations in excess of 2 mg/liter and a total load of 10 to 20 X 104 metric tons. Since this load was equal to river discharge for the entire month of April, it must have represented lateral transport of sediment resuspended in the nearshore zone. Verti- cal profiles over the middle and outer shelf for the rest of the year were characterized by sharply bounded turbidity maxima, each marking a thermal discontinuity. These also were nourished by lateral transport from the nearshore sector, where the discontinuities impinged on the sloping bottom. The near-bottom nepheloid layer was the most turbid zone in the inner shelf. This nepheloid layer was invariably the coolest and was invariably iso- thermal, indicating that its turbidity was the result of turbulence generated by bottom-wave surge. Bottom turbidities ranged from 50 mg/liter during the flood to 4-6 mg/liter during the next winter, but were at no time dense enough to drive density currents. Thus transport of suspended sediment across shelves undergoing allochthonous sediment action would appear to be a matter of introduction by a river jet, deposition, resuspension, intervals of diffusion and advection by coastal currents in a near-bottom nephaloid layer, and further deposition and resuspension. As a consequence of the intermittent nature of transport across the aggrading shelf surface, the fractionation of sediment by particle size, charac- teristic of the terrestrial environment, continues (Figs. 14 and 16). This process of progressive sorting is not a matter of the "fines outrunning the coarse"; it is a consequence of decreasing bottom-wave energy, and loss of the coarsest fraction each time there is resuspension is due to currents weaker than the preceding episode Swift et al., 1972c). The broad, gentle textural gradients of allochthonous shelves are characteristically coast-normal, al- though water mass advection is more nearly coast- parallel. The gradients reflect the greater role of bottom-wave energy gradients and sediment diffu- sion on fine-grained allochthonous shelves; grain- size gradients on coarse-grained autochthonous shelves are due primarily to sediment advection. Like many shelves undergoing allochthonous sedimentation, the allochthonous deposits on the Niger Shelf appear to incompletely cover the older autochthonous deposits; "windows" of the latter show through (Fig. 14). This does not necessarily indicate a transient state, however; as suggested by McCave (1972), it may be a steady-state phenOme- irtt owwr r*o* atis or srmttTmr ACROSS DELTA Fig. 16. Grain size in relation to sedimentary environments in Niger Delta area. In subaerial delta, all grades present are shown. In offshore part of delta, coarsest grade in near- surface layers is projected on to vertical plane perpendicu- lar to axis of delta symmetry. From Allen, 1964. non. McCave notes that the localization of zones of mud deposition depends on the balance between the near-bottom "hydraulic activity" and the near- bottom suspended sediment concentration, rather than on either of the factors above. Bare outer shelves may be zones where fines are bypassed in steady-state fashion owing to increased tidal and wave energy on the shelf edge, breaking internal waves, or impinging oceanic currents. SHELF SEDIMENTARY REGIMES AND CONTINENTAL SHELF CONSTRUCTION The varying pattern of shelf sedimentation in time and space is compatible with the concept of plate tectonics. Inman and Nordstrom (1971) have classified coasts as traUing-edge coasts (facing a spreading center), collision coasts (bordering a sub- duction zone or transform fault), or marginal coasts (facing an island arc). The full cycle of shelf development is seen on trailing-edge coasts. Neo-trailing-edge coasts (In- man and Nordstrom, 1971) of the Red Sea type are steep, as they are basically tectonic surfaces, as yet little modified by erosion and deposition, and they are high, presumably due to proximity to the ther- mally elevated spreading centers. The height of land is close to the shoreline; numerous steep small rivers deliver abundant coarse sediment. A tectonic margin regime prevails; because of the steep slope, gravity dispersal dominates. Shelves of collision coasts may never evolve beyond this stage, owing to consumption of sediments by subduction. With continued spreading, the continental mar- gin slowly subsides. The regional gradient of the 1158 Shelf Sedimentation 131 continent reverses so that the drainage area serving the coast increases. Its sediment load increases and its drainage pattern becomes more integrated. As the gradient of the submarine slope decreases, gravity dispersal becomes less efficient; a sediment prism accumulates, whose upper surface is hy- draulically maintained (graded) at a yet-lesser slope. Gravity dispersal is now confined largely to the continental slope. In zones where it has been particularly efficient, however, the original gradi- ent is retained in the form of submarine canyons extending back into the prograding shelf (Rona, 1969). With further crustal subsidence, the alloch- thonous regime becomes dominant. Sedimentary grading of the continental margin surface extends into the subaerial zone, as fluvial and estuarine depositional environments. The grading process be- comes largely self-maintaining. As long as the sedi- ment load is adequate, the coastal environments prefilter it for maximum mobility and inject it onto the shelf by means of estuary jets, and shoreface and downdrift bypassing. All parts of the shelf surface are nourished and interact with the hy- draulic regime so as to aggrade to the appropriate depth. Marginal coasts, if possessed of an indepen- dent mechanism of subsidence, may begin a cycle of shelf construction at this stage (Bally, in Isacks et al., 1973). Trailing-edge shelves are most liable to alloch- thonous sedimentary regimes, but these are prob- ably never uniformly developed over great dis- tances. Differential subsidence results in continued integration of the stream net, and the resulting master streams tend to preferentially seek loci of maximum subsidence, where they build deltaic piles beneath surfaces undergoing allochthonous sedi- mentation. Intervening shelf sectors may be suf- ficiently starved of sediment to develop autochtho- nous carbonate or clastic regimes. If the continent is of the African type (all trailing edges), areas of autochthonous sedimenta- tion must expand on continental shelves at the expense of allochthonous sedimentation, as the eroding continent approaches base level and terri- genous sediment production declines. Unfortu- nately, the type example of Africa is a poor one, as its nascent rift system has resulted in continuing relief. The Cambrian continents are probably a better reference, as the basal Cambrian sandstones are good examples of the residual sands produced by autochthonous sedimentation (Swift et al., 1971a). Cambrian platforms were subjected to a mixed regime, however, as outer-shelf mud belts followed the landward retreat of the sands. The earth appears to have been subject to cyclic eustatic sea-level fluctuations as a conse- quence of variations in the volume of ocean basins; continents have flooded as increased spreading rates have expanded the volume of mid-oceanic ridges at the expense of oceanic basin volumes. Slower spreading rates have reduced ridge volume and caused withdrawal of marginal seas (Rona, 1973). This cycle has proceeded at rates sufficiently slow (10-20 my) relative to the rates of other vari- ables so that coastal boundaries during the trans- gressive and high-stand phases were permeable, resulting in sediment bypassing and the buildup of enormous marine sediment prisms. Regression has served mainly to introduce a subaerial erosional regime to the shelf surface, with gravity bypassing over the slope, and consequent aggradation of deep- water environments (Rona, 1973). A second type of modulation has been the rapid eustatic fluctuations associated with ice ages. Here regressions have been the significant agents of marine deposition on continental shelves. The most recent deglaciation of the Quaternary ice age has transpired within the past 15 years (Milliman and Emery, 1968), resulting in a sea level rise so rapid that the intracoastal zone of estuaries and lagoons became an effective trap for the fluvial sediment input. Sediment was released to the sea floor only after stratigraphic storage, and only then in small volumes, and an autochthonous regime prevailed. During glacio-eustatic regressions, estuaries be- came deltas, and there was sufficient filtering and estuary jet injection of mobile fine sediment to significantly aggrade the shelf floor before passage of the retreating shoreline. Subaerial exposure apparently did not last long enough during the brief lowstands for extensive erosion of the regressive deposits. Emery and Milliman (1971) have noted that the Quaternary record within the Hudson shelf-edge delta consists of a series of acoustically opaque reflectors (mainly transgressive shoreline deposits) and acoustically transparent interbeds (finer high- stand and regressive deposits). Much of the neo- trailing-edge shelf of the Costa de Nayarit, Gulf of California, was formed in this way (Curray and Moore, 1964). The cyclothems of the Permo-Carbon- iferous glaciation are likewise dominated by regres- sive deposits (Fischer, 1961). The cores of the great construction shelves of the trailing-edge coasts of the Atlantic rift ocean ESTUARINE FLUVIAL SAND. CLAY SAND FINE, MUDDY SHELF SAND Fig. 17. Simplified schematic diagram of facies of the North American Atlantic Shelf at Cape Hatteras. Interpretation based on Swain (1952). Maher and Applin (1971), and Swift and Heron (1969). 1159 132 Continental Margins were built during the Cretaceous when the slow postrifting subsidence coincided with a major trans- gression (Fig. 17). The Hatteras Light Well No. 1 bottoms at 10,054 ft in granitic rock (Maher and Anplin. 1971). It is overlain bv over 1.000 ft of coarse feldspathic sand and conglomerate, the product of a tectonic margin regime, and perhaps in part of gravity dispersal. This material is in turn overlain by up to 4,000 ft of interbedded fine sand- stone and limestone of Early Cretaceous age. These beds are the offshore facies of the Cape Fear Formation (Swift and Heron, 1969), a coarse, pebbly sand of the inner coastal plain of fluvial, estuarine, and nearshore origin. The Early Cretaceous sedi- mentary regime was a mixed one, in which a coarse sediment input derived from a hinterland still pos- sessing appreciable relief was not always efficiently bypassed to the outer shelf, and intervals of carbon- ate sedimentation occurred. By Late Cretaceous time, the regional slope had decreased and a more extensive drainage net was delivering a finer sediment load. The littoral zone broke up into well-defined fluvial and estuarine depositional environments, and fine sand and mud were bypassed to all parts of the Cretaceous shelf in sufficient volume to overwhelm carbonate sedimen- tation. Regression veneered the resulting sediment pile with littoral deposits which were largely lost to erosion before the Eocene cycle of deposition. The deposits of the Eocene and Miocene are thinner, and like the Lower Cretaceous have abun- dant interbedded limestones. Associated elastics are finer than those of the Lower Cretaceous, however, and the reversions to an autochthonous carbonate regime may reflect reduced sediment supply as a function of reduced relief in the hinter- land rather than a lack of a mobile fine fraction in the sediment input. The coastal deposits of these later cycles have been largely lost to erosion. Thus the vast sediment piles of the world's constructional (trailing edge) shelves appear to be the product of repeated depositional transgressions or "classic overlap," in which the coastal boundary filtered out the coarser traction on an intensive sediment input, and the resulting mobile Fine frac- tion accumulated beneath a surface undergoing allochthonous sedimentation. Episodes of autoch- thonous sedimentation are represented by carbon- ate strata, or if the climate was inappropriate, by thin, coarse, condensed horizons of lag sands which are difficult to recognize, especially in the subsur- face. ACKNOWLEDGMENTS This paper is a contribution of the COMSED (Continental Margin Sedimentation) Program of NOAA'S Atlantic Oceanographic and Meteorologic Laboratories. Much of the information was assem- bled in the course of a study of shelf sedimentation conducted for NOAA's MESA (Marine Ecosystems Analysis Program). Data on the Virginia and North- ern North Carolina Coast were collected on cruises E-21-71 and E-5-73 of Duke University Marine Lab- oratory's research vessel EASTWARD. The EAST- WARD is supported by NSF grant GB-17545. BIBLIOGRAPHY Allen, J. R. L., 1965, Late Quaternary Niger delta, and adjacent areas: sedimentary environments and litho- facies: Am. Assoc. Petr. Geol. Bull., v. 49, p. 547-600. , 1970a, Physical processes of sedimentation: New York, American Elsevier, 248 p. 1970b, Sediments of the modern Niger delta: a summary and review, in Morgan, J. P., ed., Deltaic sedimentation, modern and ancient: Tulsa, Okla., Soc. Econ. Paleontologists and Mineralogists Spec. 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Bassin Aquitaine 1974, n> 7, p. 171 - 189 ESTUARINE AND LITTORAL DEPOSITIONAL PATTERNS IN THE SURFICIAL SAND SHEET CENTRAL AND SOUTHERN ATLANTIC SHELF OF NORTH AMERICA fi.l.P SVIF T - hlantie Oceanograpkic & Meteorological Laboratories 15 Rickenbacker Causeway Miami, Florida 31149 P *<'E-\RS - Institute of Oceanograph\ Old Dominion University \orfolk, I irginia The surficial sand sheet of ihe Middle Atlontic Bight is the product of erosiono! ihore.loce retreat. Its morphologic-strat igrophic fobric is relatively simple off straight coasts, out becomes complex in zones which ore the retreat paths of estuary mouths ; retreat of these ■eotures generotes she If volley complexes (shelf valleys paired with estuor ine shool.retreot mas- sifs'. The interfluves between adiocent shelf volley complexes moy be mantled with thin, simple shore-foce retreat blankets. The changing morphologic and dynamic characteristics of the Atlantic shoreline between Cape Cod and Florido are reflected in anologous changes in the mor phologic-strot igro- phic fobric of the surficial sand sheet. Estuaries ore smaller and more closely spaced in the Georgia Bight than the Middle Atlontic Bight , the long straight coastal comportments of the lat. ter are replaced by closely spaced, orcuote, estuary-mouth shoals. The corresponding fabric of the surficial sond sheet is that of on estuor me retreat blanket, composed of coolescing shelf valley complexes . The Carolina salient, between the Georgia Bight ond the Middle Atlantic Bight, experiences o more intense wove climate than do the adiocent shelf bights. Its littoral drift jvsiems nourish o series of large cuspate forelands. These may hove been initiated os cuspate deltas, but now a presumably se If-ma into inig. The surficial sond sheet of the odiocent shelf oc- ,«oi! >o possess a morpholog ic -stratigrophic fobric of cope shoal-retreat massifs alternating »,n shore-face retreat blankets. On the southern margin of this province, cope shoal-retreat massifs off small, closely spaced cuspote forelonds coalesce into o cope retreat blonket. INTRODUCTION The Central and Southern Atlantic Shelf of Borth America is veneered by a discontinuous sheet of well sorted sand that tends to be more homogeneous than the older Holocene and Pleistocene substrate on which it rests. Evidence has been presented (Duane and others, 1972; Swift and others, 1972b) which indicates that this sand sheet is mainly of autochthonous or in situ origin, having formed as a residuum by a process of erosio- nal sbore-face retreat during the Holocene transgression. Two components may be discerned in the morphologic and stratigraphic fabric of this sand sheet. Large- scale components tend to be shelf -transverse, and are generally of relict nearshore marine origin. They constitute the retreat paths of zones of erosion or anomalously high deposition in the transgressing sub-littoral zone. The small scale component of the topographic and stratigraphic fabric is a nearly shelf-parallel ridge and swale structure. It is of complex origin, and may be initiated in one of several manners (Swift and others, in press), but appears in general to be a post -transgression response to a Holocene hydraulic regime, characterized by intermittent south-flowing storm currents. Where both can be clearly resolved, the large-scale comp onent appears to have been the first to form; the small-scale component is superimposed upon it. In portion of the central and southern Atlantic shelf with moderate to mild wave climates, (Georgia Bight; Middle Atlantic Bight) the large scale component of the morphologic and stratigraphic fabric may be correlated with 1164 172 Depositicnal provinces and controlling factors for the central and southern Atlantic shelf. Sediment discharge from "eade, 1969; wave climates from Do Ian , 19 7 3. _ c^l? s Vf / SUtF-iCl >m«nM SUB5U"f*Ci INMBMO CMANNtl SHOAl BfTBfAl MASS CUfSTAS '.hhi fDGI MID .JHIll Dt iANO tlOCtS 'ig. 2. First-order morphologic elements in the Middle Atlantic Bight and overprinted ridge and swale topography. tributary channels of Block Valley from McMaster and Ashraf, 197 3. Details of Chesapeake Bay mouth from Meisburger, 1972. Albemarle Valley from Sears, 1973. Other details as cited in Swift and others, 1972. 1165 173 » -.udson Shelf Valley may be in part due to the proximity of the fall line. The fall line (inner margin of coastal plain strat) converges northward through the Middle Atlantic states with the shoreline, and crosses the latter at New York. Trie northern New Jersey and Long Island shelves exhibit the considerable subaerial erosional relief characteristic of the subaerial inner coastal plain (Swift and others, 1972b). Veatr.h and Smith (1939) have sug- gested that the particularly deep incision of the Hudson Shelf Valley (locally in excess of 35 meters) may be a consequence of high melt-water discharge during Pleistocene interstadials; and that the Hudson mav have received the discharge of the Great Lakes at some period. Other shelf valleys appear to be intermediate in origin, between constructional marine retreat paths of estuarr mouth and erosional subaerial valleys with axial fills of estuarine deposits. The Long Island Shelf Valley, whose drainage basin lies entirely seaward of the present shoreline, seems to preserve a well defined subaerial pat- tern, whose characteristics are intermediate between a trellis pattern (structurally controlled) and a dendritic pat- tern (homogeneous substrate). This pattern may have survived the transgression because it was shielded by a low promontory fcm northeast storm waves. Stratigraphy of the Shelf Valley Complexes The above conclusions are a serendipitous result of our inheritance of a century of careful mapping of the Atlantic shelf surface. The morphologic evidence presented is deductive and inferential in nature. In recent years more conclusive stratiefaphic evidence has been obtained in some localities through direct examination of the surficial sand sheet by means of grab sampling, coring, seismic profiling, and radiocarhon dating. Seismic profiles, vibracores, and radiocarbon dates indicate that on the Virginia shelf, the Virginia Beach and Albermarle Shoal Retreat Massifs are planoconvex in cross section (Swift and others, in press). These flat bottomed sand ridges have been vibracored (fig. 7) and radiocarbon dates from the vibracores indicate a Holocene Age. They have a two-fold internal structure, with cores of fine muddy sand and mantles of mainly medium to coarse sand. The fine sand con- tains occasional Ostrea shells, and is believed to date from the earlier estuarine stage. The outer mantle contains a p.-- icypod assemblage in which Spisula is abundant and Donax is occasionally represented; it is believed to repre- se::, a later stage during which the shoal retreat massif was remolded by the shelf hydraulic regime into a comb-like pattern of cross-ridges and swales. SheLf valley fills tend to be concavo-convex; in cross section a surface channel is impressed into the fill which in turn lies in a subsurface channel. The surface and subsurface channels, however, are only approximately coincidEnt (figs. 2, 5; 6) and may be locally separated by many kilometers, indicating that the retreating estuary mouth shifted sideways along the shoreline as it retreated, and often "jumped the track" of its subaerial valley. Multiple strong con- cave-upwards reflectors in shelf valley fills (fig. S) may reflect such meandering during the course of Holocene estuary retreat, or may indicate repeated occupation of the shelf valley during successive Pleistocene transgressions, with incom- plete erosion during the intervening glacial intervals. Thus the Pleistocene-Holocene contact may lie either within or at the base of the channel fill. The upper strata of the shelf valley deposits consist of fine to very fine sand, or in the case of the Hudson Shelf Valley, sandy mud (Milliman and others, 1972). The fine sand appears to have been deposited after retreat of the estuary mouth, as south -trending strom currents remolded the north side shoal retreat massifs (fig. 8). Fine sand winno- wed out of the shoal retreat massifs, as the flow field constricted, would have been deposited in the shelf valleys as the flow field expanded and lost competence (Swift and others, in pr&ss a). The surficial sands of those shelf valley complexes of the Middle Atlantic Bight, which would have received glacial melt water, are richer in feldspar, as a result of en- richment by river sands draining the piedmont (fig. 9); feldspar-poor sands on the interfluves between shelf valley comple- xes are the product of shoreface erosion of multicycle coastal plain sediments. Morphology and Stratigraphy of I nterfluves The morphology and stratigraphy of the interfluves between the shelf va lley complexes of the Middle Atlantic Bight nave been described elsewhere (Stahl and others, in press; Stubblefield and others, in press, McClennen, in press McKinney, in press) Swift and others in press. The information will be summarized here to complete the picture of the depositional fabric of the surficial sand sheet. The surficial sand sheet is thinner on the interfluves, ranging from 0 to 20 m thick. The thickness variation is a consequence of its characteristic second order morphologic element, the ridge and swale topography, (Swift and others, in press b). Less obvious first order elements are the series of terrace and scarps (McClennen, in press, Emery, 1973) on which the ridge and swale morphology is impressed. 1166 MODERN ESTUARY MOUTH SHOAL, TIDAL CHANNELS PAIRED FLOOD CHANNEL RETREAT TRACK, ESTUARINE SHOAL-RETREAT MASSIF 40M SCARP TRANSGRESSED CUSPATE DELTA; (CAPE SHOAL- RETREAT MASSIF) 60M SCARP Fig. 3. Delaware Shelf Valley Complex (Uchupi, 1970) Isobaths in meters . Zi~ - =j= *• "-■K~ " ( . > " '•$S\ ■* -V ■-'i -^ -^ : , s r* " ->' '-Y- '-. y i *;-- m -"'//«• i -, \ OOC V i.-,P14Tr MASSIF' -' GON lN[fl V_ ; ft ,'|g>, "-- -^^,c ;; Fig Morphology of the Former Albemarle River surface channels from unpublished data o O'Connor, East Carolina University, Gree Beach Ridges from Fisher, 1967. Contour 1167 ] TlOU th. Sub- f Ri ggs and nvil le, N.C. , s in feet. 175 wro*Hi c J * i 401- *0- 1 ' 1 " J ! APfAIINl 0» 1-- 6 I 10 coMTowa n Fin to ■otto* Fig. 5. Virginia Beach Shelf Valley. Seismic profiles from Shideler and others, 1972. Contours in feet. SURFACE CHANNEL 75'40' SUBSURFACE CHANNEL Fig. 6. Surface and subsurface channels at the mouth of Chesapeake Bay. Subsurface channel (from Meisburger, 1972) may be a product of subaerial fluvial erosion. Upper surface channel appears to be the Holocene retreat path of the main estuary flood channel. This channel was blocked by southward growth of the-, zig-zag shoal system south of Cape Charles since the late Holocene reduction in the rate of sea level use (Ludwicke, 1973) and a new flood channel has formed to the south. 1168 176 0 3 0^ SURFICIAL SANO ESTUARY MOUTH SAND PLEISTOCENE SUBSTRATE VERTICAL EXAGGERATION 200. ;•:■;■: COASSE. VER" COARSE SANO C ~> ^ (g ~ MECIUM SANC FINE SANC •«- "•!£ SANC fi Fig. ?. Above: Seismic profile and vibracore section through Piatt Shoals , the shoal retreat massif on the south side of the Albemarle Shelf Valley. Below: detail of vibracore section. A: Surficial sand, B: Estuary mouth sand, C: Pleistocene substrate. Modified from Sears, in press. See Fig. 4 for location. 1169 177 the character of the stream net on the adjacent modern coast (fig. 1). However, off the Carolina Salient, with its intense wave climate, the pattern of littoral drift constitues a second causative factor. The surficial sand sheet of the central and southern Atlantic Bight may be divided into a series of morphologic -stratigraphic pro- vinces which reflect both the physiography of the retreating coast and the coastal sedimentary regime. THE MIDDLE ATLANTIC BIGHT: SHELF VALLEY COMPLEXES AND SHORE-FACE RETREAT BLANKETS Morphology of Shelf Valley Complexes In the Middle Atlantic Bight, between Cape Hatteras and Cape Cod, the shelf surface consists of a series of transverse shelf valleys, separated by plateau-like interfluves (fig. 2). On close inspection, the shelf valleys are seen to comprise an association of both negative topographic elements (shelf valleys in the strict sense; sub- marine canyons) and positive topographic elements (midshelf and shelf edge deltas; and estuary shoal retreat mas- sifs). This association will be referred to as a shelf valley complex . The criteria for identifying shelf valleys and submarine canyons are self evident. Shoal retreat massifs are broad ridges sited (usually) on the north flanks of shelf valleys, usually more or less dissected by the shelf hydraulic regime into a comb-like pattern of cross ridges and swales. Uniformitarian considerations suggest that their origin may be determined by tracing the ridges landward to the modern coast. This is not always possible, since the chan- ge in the rate of sea level rise prior to 4,000 years ago (Milliman and Emery, 1968) has modified sedimentation pat- terns at estuary mouths and has locally sealed them off from the shelf. The Delaware Shelf Valley, however, is exemplary (Swift, 1973), in that Delaware Bay-mouth Shoal, a depositional locus for the littoral drift system of the New Jersey Coastal Compartment, and the Delaware shelf Valley may similarly be traced directly into the major flood channel that breaches this shoal on the south side of the estuary mouth (fig. 3). Thus these two morphologic elements do not, in genetic terms, comprise simply a drowned subaerial river valley but instead are submarine cons- tructional features that define the retreat path of the estuary mouth through late Holocene time. This interpretation is compatible with the morphology of the Albermarle, Virginia Beach, Susquehanna, and Great Egg Shelf Valley Complexes (fig. 2). However, all of these complexes have become disassociated to a greater or lesser degree fom their parental estuaries. The late Holocene reduction in the rate of sea level rise appears to have resulted in the detachment of the mainland beach on either side of the ancestral Albermarle River in the manner des- cribed by Hoyt (1967). Littoral drift nourished the beach, allowing it to rise with sea level, while lagoons crept north and south behind the dunes. When the southern lagoon (Roanoke Sound) connected with Pamlico Sound, sufficient river and tidal discharge was apparently diverted southward so that the detached river mouth be sealed (fig. 4). The shelf valley now terminates abruptly in the shore face of Currituck Spit. This event appears to have transpired between 5,000 and 7,000 years ago (Sears, in press). The Virginia Beach Shelf Valley (fig. 5) has been tentatively identified as the retreat path of the ancestral James Estuary (Swift and others, 1972b, in press). With the transgression and flooding of the Susquehanna Valley, the James Estuary was captured and is now a tributary estuary of Chesapeake Bay. The Chesapeake Shelf Valley may be traced into the seaward face of the Chesapeake Bay-mouth shoal (fig. 6). The enlargement of this shoal described by Ludwick (1973) may have been attendant on the near stabilization of the shoreline since the late Holocene reduction in the rate of sea-level rise. Growth of the shoal has apparently resulted in abandonment of the flood channel whose retreat path defines the landward portion of the Chesapeake Shelf Falley, and a new flood channel has appeared at the southern margin of the bay mouth. The Great Egg Shelf Valley (fig. 2) is associated with the insignificant Great Egg River, a river whose drainage basin lies entirely in the Coastal plain. It appears that earlier in the Holocene this river received the drainage of the Schuylkill, upper Delaware and perhaps Hudson Rivers (Johnson, 1931; McClennen, 1973; Swift and others, 1972; Sanders, personal communication, 1972). Since then the Delaware Estuary has recaptured the Delaware and Schuylkill Rivers, and the Hudson Estuary has recaptured the Hudson, if it indeed had lost it. The Block Shelf Valley (fig. 2) is in essence the retreat path of ancestral Connecticut Estuary, and the channel between Block Island and Long Island is a detached estuary mouth. The inferred submarine constructional origin for these shelf valley complexes best fits the Delaware Shelf Valley complex, and fits least the Hudson Shelf Valley complex, which is a subaerial river valley only partially filled by estuarine deposits; the other shelf valley complexes fall between these two extremes. The relief associated with the 1170 i n DIRECTION - FREOUENCY DIAMETER (*) CD I.O-I.5 CD 1.5-2.0 CD 2.0-2.5 EH 2.5-3.0 EXCEEDANCE (%) TRANSPORT (mVm), 3.0 4.2 6.7 7.3 CURRENT METER STATION 79 9.3 7.6 5.1 • STATIONS Fig. -8. Grain size map from the Virginia beach massif. See Fig. 5 for location. Note fine sand in shelf valley. Peak in current meter record rises above tidal modulation, through envelope of threshold velocities of grain sizes present. This kind of storm induced event is responsible for remodeling massif into transverse ridges and swales. See Swift and others, 1973, for explanation of calculations 1171 179 Fig. 9. Felspar distribution of the Surficial Sand sheet, Middle Atlantic Bight. From Milliman and others, 1972. Shoalinj shows feldspar: feldspar and quartz ratio in excess of 2 5 percent . DEPTH FEII — 0 MIW WEST 120 140 IftO 0ISCONFOHMITY FINE, siirr SAND -A PUISTOCENI-HOIOCENE CONTACT -»' TE»TIA«r-OUATe«NA«T CONTACT MOTTIED. OESKCATED surr clat I (A0IOCA*»ON DATE ON PIOFIIE Fig. 10. Stratigraphy of the Beach Haven sector, New Jersey Shelf Relief of surface A-A may be due to fluvial or tidal creek erosion. HI is interpreted as a lagoonal deposit. H2 is a back-barrier deposit. Contact H2-H3 is disconf ormity cut by shore-face retreat; represents missing barrier superstructure sands. H3 is transgressive marine sand sheet, the debris of erosional shoreface retreat. Cores 829, 828 penetrate modern sand ridges. Sea floor rises towards present shore face at Core 818. See Stahl and others, in press for Standard deviations of dates. 1172 180 '111 (', II I Ml |I| 5 £ < si \!< is 0 0) 3 H P k 0 fl 0 r-\ c cd cd x; ^ IX, h p o x: ^ > rfl CX •H ■ H £ 0) (0 P -H p U O i\3 U *~ rfl bO •H 0) UlrHH'H p Sh e a) a p 1! P -H > g fTj £ (1) k CD 3 U , C ^H rfl rtf -H •• 1 >H bO £ p CD 0) CO C iH > S-i C -H CD 3 O 0 13 CO CJ CO xi x: U -H rd CD < CO P U Mh cx ^^ww >e — ! j*:*:ffi/., * « >^3f^ igrimm i TTTF ^n S3 f bO •p o 1 > rQ C a> c ^ o CO •H m p fc o •H CD * 0 > •-> CO ■H c & T3 C/3 ■H r; 01 •H =T £ P. o bOTO £ P C o IP * rd & bO cp c " • • H to CO

l!»w SOUND OSSA8AW SOUND ST CAIHdINES SOUND SAMl SOUND ooeor sound Fig. 13. Georgia Bight, witn shoreface crenulated by closely spaced estuary mouth shoals. From 1200 series National Ocean Survey charts. Fig. 14 Port Royal Sound, Georgia Bight. Discontinuity between older flood channel retreat path (dashed line) and present ebb-flood channel pattern suggests progradation of estuary mouth shoal since late Holocene reduction in rate of sea level rise. Note overprinted ridge topography seaward of shoreface . 1175 183 ■ ith time. Its retreat path would consist of a furrow in the Pleistocene basement extending seaward into the snelf. These furrows would be filled with sand from the retreating estuary mouth shoal. The narrower inter- fluves would be capped bv a thinner veneer: both would be beveled by erosional shore-face retreat. The trough fill might stand higher on the sea floo: than the adjacent interfluve; or the channel may have been partially re -excavated by a larse flood channel as the shoal retreated. The Georgia Shelf seaward of the shore face does in fact exhibit a topography of subdued ridges and swales that are shore-normal in orientation and converge to- \ards the shelf edge (fig. 15). While they have been compared with the shelf parallel ridge and swale topography further north (Uchupi. 1968). this pattern would appear to be mainly of relict estuarine origin, rather than a post-transgressional response to southward storm currents as is the case for the shore -parallel ridge and swale to- pography oi the Middle Atlantic Bight. The morphologic-stratigraphic fabric of the surficial sand sheet of the Georgia Bight might thus be expected to resemble that of the Middle Atlantic Bight, except that the shelf valley complexes are closely spaced and tend to coalesce; the resulting fabric might be referred to as an estuarine retreat blanket (fig. 1*5). THE CAROLINA SHELF- CAPE SHOAL-RETREAT MASSIFS AND SHORE-FACE RETREAT BLANKETS The transition from the broad, dendritic, disequilibrium estuaries of the Middle Atlantic Bight to the nar- row, straight or meandering, trumpet -mouthed estuaries of the Southern Atlantic Bight occurs in the Carolina client between Cape Fear (Neuse estuary) and Cape Lookout (seaward of the Neuse estuary)- However, this tran- ; ition is masked bv the uniform coastline imposed on the Carolina Salient by its more rigorous wave climate. Tne Salient is dominated bv four great cuspate forelands, Capes Hatteras, Lookout. Fear, and Romain (fig. 17). it has been suggested that these capes were initiated during Pleistocene low stands of the sea, as cuspate del- "as (Hovt and Henry, 1971 ). A uniform variation on the coastal pattern may be discerned which lends this hypothesis some credence. The cape closest to the Georgia estuarine belt, Cape Romain, appears to have the strongest fluvial element (fig. 7 ;: its plan view is that of a cuspate delta, associated with the Santee-Peedee River System. Cape Fear is similarly associated with the Cape Fear River. Cape Lookout may have been served by the Neuse River prior to :ts capture bv the Pamlico system, and Cape Hatteras could have once been associated with an ancestral Pamlico R ive r With the possible exception of Cape Romain, however, rivers appear to be contributing little to the mainte- nance of these cuspate forlands today. The role of coastal erosion and wavedriven littoral drift seems dominant, particularly in the more northern capes, whose wave climate is more rigorous. Each cape marks the site of a major convergence in the littoral drift system, and before each Cape extends a shoal retreat massif, marking the retreat path of the convergence back across the shelf during the Holocene transgression (Swift and others, 1972b). Tne flu- vial role then, has been that of a triggering element, particularly in the case of the more northerly capes. They may have been initiated as cuspate deltas during the late Wisconsinan low stand, but since then they have been more or less independant, by virtue of a feedback mechanism whereby the shoal-retreat massif has served to refract the propagation pattern of storm waves from the Northeast and focus the energy on the Cuspate forelands. The pattern of refracted waves in tum maintains morphology of the retreating foreland and creates a littoral drift concergence at its apex which nourishes the landward-growing tip of the shoal retreat massif (fig. 1R). To the extent that this hypothesis is correct, it should be possible to predict in general terms the morphologic - stratigTaphic fabric of the Carolina Salient, based on the relationships between morphology and internal structure of the Holocene deposits of the Middle Atlantic Bight. On the outer shelf, deltaic deposits should be overlain by the sands of shoal -retreat massifs. In a landward direction the deltaic deposits should become ribbon-like estuarine chan- nel fills, whose courses need not conform to the course of the overlying shoal retreat massif. Between shoal retreat massifs, the thinner sheets which are the product of shore-face retreat might be expected. SOUTH CAROLLNA SHELF : A CAPE SHOAL-RETREAT BLANKET A variant of this pattern of cape shoal-retreat massif and shore-face retreat blanket appears an the South Carolina Shelf (fig. IS). Here in the transition zone between the foreland -dominated coast of the Carolina Salient and tne estuarine coast of the Georgia Bight, is a series of closely spaced small-scale cuspate forelands (fig. 19). Shoal retreat massifs may be traced for varying distances seaward from the cuspate forlands as seaward-convex bulges in the contour: These seaward-convex bulges of contours intersect in landward-facing cusps between the massifs 1176 *$£ro s K^s " 3 Fig. 15. Topography of the Georgia Shelf. Shelf valleys indicated by dashed lines; probable deltas by stipple. From Swift and others, 1972. -5 16. Morphologic pattern of estuarine shoal retreat blanket, overprinted bv ridge and swale topography, South Carolina Coast. Snort Swift and others, 1973. Highs are stippled. 1177 18b Cusr-ate Forelands of the Carolina Salient and associated shoal retreat r.assifs. Littoral drift in yds2/yr X ln0 from Lansfelcer and others, 196S. MINOI V WAVE APPtOACH .g. 18. Schematic diagram illustrating inferred transition from Cuspate delta to Cuspate Foreland. Shallow water shaded lines are wave crests; arrows are littoral drift- 1178 186 ^\ Tuspate Forelands and Cape Shoal Petreat Massifs of the South Carolina Shelf. Note overprinting by ridge and swale tooosra?'"" ZJ SHOREFACE RETREAT DEPOSIT □ PRE RECENT SUBSTRATE Q LAGOONAL MUD l~l SHOAL RETREAT DEPOSIT B SHELF VALLEY DEPOSIT 20. Schematic diagram illustrating provinces of surficial sand sheet of Middle Atlantic 3ight as defined by morphologic and stratigraphic fabric. A: Shelf valley complex and shoreface retreat blanket. 3: Estuarine retreat blanket. C: Cape shoai-retreat massif and shoreface retreat blanket. D: Cape retreat blanket. 1179 187 lence the massils are coalescing. This pattern is the reverse of the shoreline pattern, where the forlands are cuspate, and the intervening bays are arcuate, so the seaward and swale cannot be interpreted as overstepped shorelines The ridges and swale topogTaphy has been heavily overprinted on the coaslescing massifs. Troughs converge with the shoreline toward the south, and shoal in tnat direction, as they do in the Middle Atlantic 3ight, suggesting southward water transport during storms. Relief is rarely over two meters, however, sugges- ting that the surficial sand sheet is composed of somewhat finer sand, whose effective subaqueous angle of repose is verv low. The close spacing of cape shoal retreat massifs in this sector suggests that the surficial sand sheet is best described as a cape retreat blanket, analogous to the estuarine retreat blanket hypothesized fo the Georgia Coast. CONCLUSIONS The morphologic and stratigraphic fabric of the surficial sand sheet of the Central and Southern Atlantic Shelf has some of the characteristics of a streaky photogTaph taken by a camera which moved while its shutter was open. The sand sheet is a debris mantle generated by the process of erosional shoreface retreat. Its deposi- tional locus was a narrow, landward translating belt at the foot of the shore-face. Singularities in the locus, such as estuarv mouths and zones of littoral drift convergence off cuspate forelands, appear as "streaks" through shelf ;and shelf: shore-normal highs and lows which are the retreat paths of these singularities. Evidence for such a relict component in the depositional fabric is better developed in the Middle Atlantic Bight where seismic profiles, cores md radiocarbon dates are available, than from the surficial sand sheet further south where topographic maps are available, but stratigraphic data are missing. Four basic morphologic-stratigraphic fabrics are apparent (fig. 20). The relict, first-order topography of shelf transverse valleys and shoal-retreat massifs has been overprinted .\ ith a ridge and swale topography induced by the shelf hydraulic regime, but is still readily discernible. It is pro- bably characteristic of transgTessive shelves characterized by a moderate energy flux; on such high energy sectors a< the tide-swept shelf around the "British Isles (Kenyon and Stride, 1970) hydraulically induced topography has 1 argeh obliterated the older relict component. ACKNOWLEDGEMENTS This paper is a contribution of the COMSED (Continental Margin Sedimentation) Program of NOAA's Atlantic Oceanographic and Meteorologic Laboratories. Much of the information was assembled in the course oi a study of shelf sedimentation conducted for NOAA's MESA (Marine Ecosystems Analysis) Program. 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MEADE, R.H. , 1969, Landward transport of bottom sediments in estuaries of Atlantic Coastal Plain. Jour. Sed. Petrology 39: 229-234. ME5BURGER. E. P. (1972). Geomorphology and Sediments of the Chesapeake Bay Entrance. U.S. Army Corps of Engineers, Coastal Eng. Research Ctr. , Tech Memo (in press) MILLIMAN, J.D. and EMERY, K.O. (1968). Sea levels during the past 35,000 years. Science 162. 1121-1123. MILLIMAN, J.D. , PILKEY, O.H. , and ROSS, D.A. (1972). Sediments of the continental margin of the eastern United States. Geol. Soc. Am. Bull. 83, 1315-1334 OERTEL, G.F., and HOWARD, J. D., 1972, Water circulation and sedimentation at Estuary entrances on the Georgia coast, in: Swift, D. J. P. , Duane, D.B. , and Pilkey, O.H., 1972, Shelf Sediment Transport: Process and pattern. Stroudsberg, O. , DOWDEN, HUTCHINSON G ROSS, p. 411-427. PAYNE, L.H., (19?0) Sediments and Morphology of the Continental Shelf off Southeast Virginia, Ph.D. thesis, 70 pp. Columbia Univ. , New York (unpublished). PILKEY, O.H, and FRANKENBERG, J. (1940). The relict - recent sediment boundary on the Georgia continental shelf. Georgia Acad. Sci. Bull. 27, p. 37-40 PILKEY, O.H. and GILES, R. T. (1965) Bottom topography of the Georgia continental shelf . Southeastern Geol. 7, d: 15-18. 1181 189 POWERS, M.C. and KINSMAN, B. , 1953. Shell accumulations in underwater sediments and their relation- ship to the thickness of the traction zone. J. Sedimentary Petrology, 23, P. 229-234. SEARS, P.C. 1973. Evolution of Piatt Shoals, Northern North Carolina Shelf: inferences from areal geology. Master's thesis. Institute of Oceanography, Old Dominion Univ. Norfolk, Va. STAHL, L. , KOCZAN, J. , and SWIFT, D. , 1973, Anatomy of a shoreface-connected ridge system on the New iersey shelf: Implications for the genesis of the shelf surfi'cial sand sheet. Geol. (in press) SHIDELER, C.L. , SWIFT, D.J. P., JOHNSON, C.H. , and HOLLIDAY, B.W. (1972). Late Quaternary Stratigraphy oi the inner Virginia continental shelf: A proposed standard section. Geol. Doc. Am. Bull , 84: 2161-2164. STUBBLEFIELD; W.L., LAVELLE, W.J., McKINNEY, T.F., and SWIFT, D.J. P., in press. Sediment response to present hydraulic regime on the Central New Jersey Shelf. Jour. Sed. Petrology. SWIFT, D. |. P.. HOLLIDAY, B. , AVICNONE, N. , and SHIDELER, G. (1972a), Anatomy of a shoreface ridge system. ralse Cape, Virginia, Marine Geol. 12, 59-84 SWIFT. D. J. P., KOFOED, J.W., SAULSBURY, F. P. , SEARS, P. (1972b). Holocene evolution of the shelf surface, central and southern Atlantic coast of North America. In: Shelf Sediment Transport: Process and Pattern (D.J. P. SWIFT, D.B. DUANE, andO.H. PILKEY, eds). Dowden, Hutchinson G Ross, Stroudsburg, Pennsylvania. SWIFT, D.J. P., SHIDELER, G.L., HOLLuDAY, B.W., McHONE, J. andSEARS, P., (in press a). Distribution and Genesis of inner continental shelf sands, Cape Henry to Cape Hatteras. Coastal Engineering Research Center, Tech. Memo. SWIFT, D.J. P., DUANE, D. B. , and McKINNEY, T. F. , in press. Ridge and swale topography of the Middle Atlantic Bight, North America, secular response to the Holocene hydraulic regime. Mar. Geol. SWIFT, D.J. P., 1973. Delaware Shelf Valley: Estuary Retreat path, not drowned river valley. Geol. Soc. Amer. Bull 84: 2743-2748. UCHUPI. E. (1968) The Atlantic continental shelf and slope of the United States (Physiography). U.S. Geol. Surv. Prof. Paper 529-C, 30 p. VEATCH, A.C., and SMITH, P. A., 1939. Atlantic submarine valleys of the United States and the Congo submarine valley. Geol. Soc. Amer., spec paper 7, 101 p. 1182 MULTI-FREQUENCY RADIOMETRIC -MEASUREMENTS OF FOAM AND A MONO-MOLECULAR SLICK B. Au, J. Kenney, L . U. Martin Naval Research Laboratory Washington, D.C. and D . Ross National Oceanic and Atmospheric Administration Miami, Florida ABSTRACT been regi pr es The temp var i f oam 1.4 the had roug emi s ing pol a inc r 60 d serv de t e Micr owav made of on where s e d by an f can uca s er a tur es ations at emis s iv i GHz to 0. mono- mole the smne hnes s . F sion deer ocean for rization, eased abo egr ees . ed at bo t ctable at e r ad ione trie measurements have both a surf-zone and of an ocean small-scale roughness was sup- artificial nor.o-nolecular slick. ureaents show near identical foam at 8.35 and 14.5 GHz, but large 1.4 GHz. Th e resultant maximum ties at nadir range from 0.57 at 84 at 14.5 GH z. The presence of cular slick on the ocean surface effect as a d ecrease in. surface cr horizontal polarization, the eased below t hat of the surround- all viewing angles. At vertical the emission decreased below and ve a vi ewi ng angle of approximately The change in temperature was o b - h 8.35 and 14 .5 GHz, being barely 1.4 GHz. 1. INTRODUCTION The dependence of the microwave brightness temperature on sea state and surface wind fields is under active investigation and has led to the prospect of remotely determining these parameters from a satellite on an all-weather basis. The useful- ness of sea state and wind field data (in data scarce areas) would be of immense value to both meteorologists and oceanogvaphers alike. Two oceanographic effects that play important roles in the dependence of the microwave signal on the sea sur- face are snail-scale wave structure and foam. The -dependence of the observed microwave signal on sea surface structure mani- fests itself through the emission and reflection from dielectric media with all scales of surface roughness. These include not only the relatively 'smooth wind waves and swell much larger than the observing wavelength, but also the capillary and ultra- gravity waves present on the sea surface at low surface wind speeds. Current models of the sea surface include roughness both larger and smaller than the observing wave- length, but the effect of small-scale structure on the radiometric signal has yet to be experimentally verified. Foam is a potentially more useful parameter to the remote sensing of the ocean surface by microwave radiometry, beyond an initial start velocity of 7 m/sec, foam coverage increases with surface wind speed. The exact magnitude of the signal 176 3 1183 increase depends on observing frequency, areal coverage of foam in the antenna beam and foam properties. Both the dependence of foam coverage vith wind speed and the radiometric properties of foam are areas of active research. Of primary interest is the increase in temperature vith frequency and the -variation with viewing angle and polarization. , Experimental information about both of these phenomena has been obtained by the Naval Research Laboratory in a series of airborne multi-frequency radiometer measure- ments. In one set of observations, low altitude measurements were made of a surf- zone at a variety of viewing angles. In the other set, measurements were made of an ocean region In which the small-scale roughness had been suppressed by an artificial monortno 1 ecul a r slick. This suppression enabled comparison to be made between an ocean surface having .all scales of roughness present and one having just the large- scale structure. 2. INSTRUMENTATION The mea sur emen t s in these exper inents were made with a three frequency, non- scanning , airborne radiometer system mounted on a NOAA C-130 aircraft. The antennas all have identical seven-degree beam widths and were mounted on a hydraulically con- trolled platform that allowed v i ewin g angles from nadir out to 80 degrees to be ob- ta ined . The ant ennas at Ku(14 . 5GHz) and X-band ( 8 . 3 5GH z ) were horn-fed dielectric lenses w hile the L- -ba n d (1.4GHz ) ante nna was a dipole-fed eig ht foot diameter para- boloid. Periodic calibration of the radiometers was provide d by noise diodes coupled into the r e f er enc e arm of the radiometers. Simultaneous dua 1-polarization measure- ments were made at K»~ and X-b and , w hile single polarization (either horizontal or vertical) was observed at L-band. Data were recorded both on analog strip-chart for instant monitor ing pur poses an d also on magnetic tape for la ter digital processing. Sensi tiv ity of the rad iome ter s with a one second integration time was 0.21, 0.08 and 0.05 "K for L, X and K -band s res pec t ive ly . 3. SLICK MEASUREMENTS To determine the effect of small-scale roughness on the radiometric signal, cne method is to suppress the small-scale waves in a specific area on the ocean surface. Although various types of oils da it. j) small-scale waves, for sufficient oil thickness, oils have a radiometric effect of their own. This effect may overwhelm any change due to the damping of the small-scale structure. To eliminate this problem, oleyl alcohol was used for the experiment. It forms a mono-molecular slick on the ocean surface which is too thin to have a radiometric effect, yet damps out the capillary and ultra-gravity waves. The oleyl alcohol was laid by the NOAA T-boat in the Atlantic Ocean about five miles from Miami, Florida. A total of nine passes along the length of the slick was made, with measurements being taken at angles from nadir out to 80 degrees. Based on laser geodilite data, the significant wave height was about 2.4 meters. Surface winds were 8 meters/sec, sufficient to produce some foam patches on the sea surface. Corresponding 3 5-m.m photographs of the sea surface at a rate of one per second were used to confirm the areal extent of the slick. gree Fig. Ku~b in t The angl degr s imi sunm iza t po 1 a ef f e temp The s ar 2. and s empe slic es , e es . lar , ar i z ions r i za c t a er a t radi e sho The and r a tur k dec bu t p Res but ed In due t ions 1 Ku- ur e c OiCCt wn f slic for e w i r eas r odu ul ts with Fig to t inc tha hang er o or h k ap both th a es t ces obt a s s. 4 he s r ea s n X- e du utputs as a function of time for a viewing angle of zero d e - orizontal polarization in Fig. 1 and vertical polarization in pears as a 2° K decrease In antenna temperature at both X- and polarizations, with no detectable effect at L-band. The change ngle for both polarizations is summarized In Fig. 3 for K. -band, he observed temperature for horizontal polarization at all an increase in temperature for vertical polarization near 80 ained on 3 April 1973 under lighter sea state conditions are light decrease in magnitude. The results for both days are and 5, which show the temperature difference between polar- lick as a function of viewing angle. The difference between es with increasing viewing angle and shows a slightly larger band. Surface roughness thus has little influence on the e to the slick until large viewing angles are obtained. 4. FOAM MEASUREMENTS To investigate the radiometric properties of foam as a function of frequency and polarization, it is essential that the foam be identical in each case. This l/6'l 1184 vas acconpJ ishcd in the field observations by making measurements simultaneously at three frequencies and at both horizontal and vertical polarization at X- and K -band . By using identical seven degree beam widths for all antennas, different foam coverages among beams are eliminated and comparison can then be made. To obtain good foam coverage and sufficiently thick foam, observations were conducted parallel to a surf- zone. The measurements were made from an altitude of 150 meters at angles from nadir out to 53 degrees. Figures 6 and 1 show the radiometer output as a function of time for all of the radiometers at a viewing angle of 28 degrees. The wide variations in signal are due to both variations in foam properties and foam coverage. One can notice the cor- relation between the three frequencies and both polarizations, with only a difference in magnitude. To illustrate the response between the different frequencies, Figs. 8 and 9 show scatter diagrams of the temperature increase due to the foam at L- and X-bands plotted against the increase at Ku-band. The increase in all cases is the increase in brightness temperature. above that from a specular surface. The linear relationship between X- and K -bands compared to the. variability at L-band indicates that the foam was sufficiently thick to have the same response at the higher freq- uencies, but variable response at I. -band. The results for all viewing angles are summarized in Fig. 10, which shows the maximum foam emissivity at Ku-band as a function of viewing angle for both polari- zations. The results at X- and L-band are not shown as the X-band values are within 1% of those at Ku-band and those at L-band are similar in shape, only decreased in magnitude. For comparison purposes, the empirical model as put forth by Stogryn is also shown for the same conditions as the experiment. The maximum value of the experimental emissivity at nadir is 0 . 8 4 , less than the theoretical maximum of 1.0 for a perfect emitter. The results for all of the frequencies are shown in Fig. 11, which shows the observed foam emissivities as a function of frequency for nadir viewing angle. The empirical model of Stogryn is again shown for comparison. One important feature is the increase in emissivity of foam from L- to X-band and the flatness of the curve from X- to K-band. 5. CONCLUSIONS The absence of small-scale v a ves on the ocean surface chang e s the mic r owave emi ss ion at 8.35 and 1 4 . 5 GH z , and has a barely detectable effec tat 1 . 4 GH z. At hor izontal polarization, the chang e in emi s s ion is observed as a decrease in signal for all viewing angles. For ver t i ca 1 polarization , there is a d ecr ea s e in emission for angl e s less than 60 degrees an d an increase in signal b ey ond The magn i tud e of the chan ge in em i ss ion i ncreases with increasing surface roughness, particu larly for vertical polarization at lar ge viewing angles. Th e measurements show t hat the sea sur face bee omes effectively smooth er w hen the small-scale waves are d arr ped , in that the y have an exact opposite effect t 0 an inc r ea s e in surface rou ghnes s . Fur ther exp erinents are required to d e t ermine whether the increase in emission f rou small- sea le roughness is ind ep enden t of the underlying 1 arge-scale rou ghnes s , or wh e ther sma 11-scale waves become imp or tan t on 1 y after larg e-scale roughness is present. In any case , it is evident that smal 1 -sea le r ou ghne ss is impor t an t to the emission from the sea surface and must be inc lud ed i n any theor e t ica 1 mod e 1 . The presence of foam on the sea surface is responsible for large increases in microwave emission at all of the frequencies investigated. The emission varies with areal coverage and foam properties, but is less at .1.4 GHz than at the higher freq- uencies. The variability at L-band is caused primarily by variations in foam depth, which are more important at the longer wavelengths. The emission from the foam is less than from a perfect emitter, but it is within 16% of that value at 14.5 GHz. For the thick foam of this experiment, the emissivity of foam increases gradually from 1.4 to 8.35 GHz, with neglible increase from 8.35 to 14.5 GHz. In general, the observed foam emissivities disagree with the empirical model of Stogryn, being up to 20 "K greater in magnitude than his model. For the conditions of this experiment, where relatively thick foam was observed the frequency dependence occurs between L- and X-band. More experimental work is required to determine if this frequency dependence holds in general. It is unlikely that the emissivity of foan would have the same frequency dependence or magnitude for the foam patches and streaks on the sea surface during high wind conditions. For the thinner foam patches and streaks, the change in emissivity would most likely occur at higher frequencies. 1765 1185 Q CE CQ I o i ce: Q_ Q v^^As^A^^V~VS[ I- SLICK V'W^M, /A^ i 10 time(sec) 20 FIGURE 1. ANTENNA TEMPERATURES ALONG SLICK. Horizontal polarization, Frequencies = 8.35 and 14.5 GHz, Viewing angle = 0° , 11 April 1973. 1766 1186 135T > Q 1 125 i 1151 /^A/v ^i— SLICK A yN. /--v^ V^-~>'w X o / / *-~~^ X LIGHT I 1 . 1 0 i 10 30 50 NADIR ANGLE (deg.) TO 90 FIGURE 5. ANTENNA TEMPERATURE DIFFERENCE BETWEEN POLARIZATIONS VERSUS VIEWING ANGLE. Light and moderate surface roughness, Frequency ■» 14.5 GHz, 3 and 11 April 1973. 1769 1189 a 2 cc CD I -XL 300t 150- 0-1- cc: 300 x 5 x 5 150 CO I 0 JL 15 30 time(sec) 45 FIGURE 6. ANTENNA TEMPERATURES ALONG SURF-ZONE. Horizontal polarization, Frequencies = 8.35 and 14.5 GHz, Viewing angle = 28°, 6 June 1973. 1770 1190 o 2 ac CD i 300 t 150- 01 a 2 cc I X 300 t 150-- Q1 a 2 CC CO I 300 t 150-v -L 15 30 time(sec) 45 FIGURE 7. ANTENNA TEMPERATURES ALONG SURF-ZONE. Vertical polarization, Frequencies » 1.4, 8.35 and 14.5 GHz, Viewing angle = 28°, 6 June 1973, 1771 1191 DELTA TEMP^-BAND) FIGURE 8. SCATTER DIAGRAM OF TEMPERATURE INCREASE DUE TO FOAM AT L- AND KU-BANDS, Vertical polarization, Viewing angle = 28°, 6 June 1973. 12(3 30 DELTA TEMPfKy-BAND) *K FIGURE 9. SCATTER DIAGRAM OF TEMPERATURE INCREASE DUE TO FOAM AT X- AND KU~BANDS. Vertical polarization, Viewing angle = 28° , 6 June 1973. 1772 1192 10 0.75 > to co 2 050 Z < o u. 0.25 : °- -cT— &,-.. OVP OBSERVED VALUES STOGRYN'S MODEL I 1 10 20 30 40 NADIR ANGLE (deg.) 50 60 FIGURE 10. EMISSIVITY OF FOAM VERSUS VIEWING ANGLE, Horizontal and vertical polarization, Frequency = 14.5 GHz, 6 June 1973. 1.0 0.75- > > # 0.50 2 2 2 0.25 o ^"' ' , — / d OBSERVED VALUE l l l i STOGRYN'S MODEL 1 1 7 9 FREQUENCY (GHz) 13 15 FIGURE 11. EMISSIVITY OF FOAM VERSUS FREQUENCY. Viewing angle ■ 0°, 6 June 1973. 1773 1193 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER IN UNDISTURBED TRADE WINDS OVER THE ATLANTIC OCEAN ERNST AUGSTEIN and HEINER SCHMIDT University of Hamburg, Hamburg, F.R.G. and FEODOR OSTAPOFF NOAA, AOML Miami, Florida, U.S.A. (Received 4 July, 1973) Abstract. During the Atlantic Expedition 1965 and the Atlantic Tradewind Experiment (ATEX) 1969, shipborne aerological measurements were obtained in order to investigate the thermodynamical and kinematic structure of the planetary boundary layer in low latitudes. Under suppressed convec- tion, the subdivision of this layer into five sub-regions was found to be a rather permanent feature. Enhanced cumulus convection effects a smoothing of the thermodynamical discontinuities and leads sometimes to a destruction of the trade inversion. Due to the surface pressure distribution and the thermal wind distribution in the lower atmosphere, the actual wind speed and direction are nearly constant with height below cloud base. In the cloud layer up to the inversion, the wind speed generally decreases and the air flow tends to become more zonal. 1. Introduction In this paper we refer to the planetary boundary layer as that part of the atmosphere where physical processes induced at the sea surface are detectable. From budget calculations in the Atlantic SE and NE trades published by Augstein (1972), Augstein et al. (1973), Holland and Rasmusson (1973) and Nitta and Esbensen (1973), there is observational evidence that the planetary boundary layer, defined as above, extends between the sea surface and the trade inversion under weak to mode- rate convective conditions. The great importance of the moist layer below the trade inversion in respect of atmospheric energy transfer processes was emphasized many years ago by von Ficker (1936a) for the Atlantic trade-wind regime. Riehl et al. (1951) confirmed these results for the NE trades over the Pacific Ocean. Aircraft measure- ments over the Caribbean Sea conducted by Bunker et al. (1950) demonstrated that the atmospheric layer below the trade inversion is characterized by further disconti- nuities in the vertical temperature and humidity distribution. Lately the multilayered structure of the trade-wind boundary layer has been observed by several investigators (Garstang, 1972) and may be regarded as typical for undisturbed conditions. Parameterization schemes and theoretical models of the planetary boundary layer as developed by Deardorff (1972), Betts (1973) and Tennekes (1973) can only be verified by detailed quantitative investigations of the time and space variations of the vertical distributions of temperature, humidity and wind velocity as well as the fluxes of Boundary- Layer Meteorology 6 (1974) 129-150. All Rights Reserved Copyright © 1974 by D. Reidel Publishing Company, Dordrecht - Holland 1194 130 E. AUGSTEIN ET AL. sensible and latent heat and momentum. While estimates of the horizontal and vertical energy transports have been reported recently by Augstein (1972), Augstein et al. (1973) and Holland and Rasmussen (1973), this study concentrates on the description of the vertical thermodynamical and kinematic structure of the planetary boundary layer. Our discussion is mainly based on radiosonde and radar wind measurements obtained during a single ship expedition in 1965 (Brocks, 1970) and the Atlantic Trade Wind Experiment (ATEX) 1969 with four ships (Brocks, 1972), both in the tropical Atlantic Ocean. 2. The Data In 1965, intensive aerological measurements were carried out (a), on a meridional cross-section along 30° W longitude between 32° N and 6°S latitude in August and (b), at the anchor station of the German R.V. 'Meteor' at the equator near 30°W from 12 September to 1 1 October. On the north-south passage, the ship traversed a tropical depression within the NE tradewind region and the Equatorial Trough Region. At the anchor station, well developed Southeast trades prevailed and with the exception of three days, convection was suppressed throughout the entire period. The steadiness of the surface wind was as high as 97%. Low-level radiosonde and radar wind measure- ments were obtained at 6- and 3-hr intervals. ATEX lasted from 6-21 February, 1969 in the Atlantic Northeast trades. The three research vessels 'Discoverer', 'Meteor', and 'Planet' formed a drifting equilateral triangle with a side length of about 400 n. mi which was centered at 1 1 ° N and 37° W as shown in Figure 1. The data of the fourth ship, the British HMS 'Hydra', which was located between the 'Discoverer' and the 'Meteor' during the first part of the experi- ment, will not be discussed in this context. All ships released simultaneously eight radiosondes a day and tracked them by radar to obtain radar winds. This data set is specifically suitable for boundary-layer studies. In order to obtain a high resolution of the vertical temperature and water vapor profiles, special measuring techniques were employed. At the 'Discoverer', every balloon carried two modified U.S. 403 MHz radiosondes, one reporting temperature and the other relative humidity as functions of pressure. From the other ships, regular radiosondes were launched twice a day and three-channel structuresondes six times per day. The structuresondes provide continuous measurements of dry- and wet-bulb temperature as functions of pressure. The tracking unit of the wind-finding radars on the three ships at the corners of the triangle were of the type Selenia Meteor 200. Unfortunately, radar wind observations from ships are rather poor in the lowest 500 m because the balloon release point is too close to the radar antenna and the radar cannot lock on the target at distances closer than a minimum slant range. In order to get at least some insight into the details of wind distribution in this layer, about 20 balloons with slow ascent rates were started from a rubber raft at a distance of 500 to 800 m from the ship. The reduction proce- dures of the radar and radiosonde data are discussed extensively by Brummer et al. (1973). 1195 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 131 longitude 50° W 40° 30c 20* 10e . ^7? 1 \ AFRICA vfl ^ ^— SOUTH AMERICA 20° N 10' 3 10° s Fig. 1. The ATEX triangle at the beginning, middle, and end of the experiment. Location of the ships: 'Planet' at the north-east, 'Discoverer' at the north-west and 'Meteor' at the south corner. Concerning the large-scale weather conditions, ATEX may be subdivided into two periods. The first period (6-12 February, 1969) was characterized by surface winds of about 9ms-1 and depressed convection at all ships. During the second period (13-17 February), the subtropical high pressure cell was partly divided by a mid- latitude trough, the meridional pressure gradient between the high and the Equatorial trough became rather small and the speed of the trade winds decreased to6ms"' and less. Furthermore, the northern fringes of the Equatorial cloud band covered the southern region of the ATEX triangle. Consequently, cloudiness increased; cumulus congestus and a few cumulonimbi with rain showers were observed at 'Meteor'. No significant rainfall occurred near the other ships. The typical weather situation for the two time periods is illustrated in Figure 2 which shows the synoptic surface charts for 9 and 14 February and in Figure 3 which shows satellite photographs for the same dates. 3. The Vertical Distribution of Temperature, Water Vapor and Wind Velocity 3.1. Temperature and water-vapor profiles Mean profiles of air temperature and specific humidity at the three corners of the ATEX triangle during the two periods are portrayed in Figure 4. In. accordance with Bunker et al. (1950) we distinguish between the following subdivisions of the planetary boundary layer: (a) The surface layer between the sea surface and approximately 1000 mb (~ 100-m 1196 132 E. AUCiSTEIN ET AL. 9.2.1969 40° N U.2.1969 50°w A°c 30c 20e 10c 40° N 30 « 20< 10c Fig. 2. Surface pressure analysis for the 9th and 14th of February, 1969. Axis of the Equatorial cloud band is indicated by dashed lines. 1197 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 133 as o -C 60 1198 134 E. AUGSTEIN ET AL. Fig. 4. Mean vertical profiles of temperature (T) and specific humidity (q) at the ships 'Planet', 'Discoverer', and 'Meteor' during ATEX. First period (7.2-12.2): full lines; second period (13.2-17.2) dashed lines and without an inversion at 'Meteor1 dash-dotted lines. Horizontal bars at q mark the lifting condensation level. The dotted lines indicate the dry adiabatic and saturated adiabatic lapse rate, lower and upper part, respectively. height) with an adiabatic temperature gradient and a decrease of specific humidity with height which results in a slight statical instability. (b) The neutral stratified mixed layer, which may extend upward to about 940 mb, has also an adiabatic temperature lapse rate but a nearly constant vertical specific humidity distribution. (c) The overlying transition layer with an average thickness of 100 m, which is marked by a nearly isothermal temperature distribution and a strong upward decrease of moisture. Because the lifting condensation level of surface air parcels almost coincides with the top of the transition layer, it separates the regimes of cloud con- vection above from those of dry convection and mechanical mixing below. (d) The cloud layer, extending from the top of the transition layer to the base of the trade inversion, which is characterized by a temperature gradient slightly stronger than the moist adiabatic lapse rate and an upward weak decrease of specific humidity Thus, the density distribution is conditionally unstable. (e) The planetary boundary layer is topped by the trade inversion which has, a distinct increase of temperature and a steep decrease of specific humidity. Conse- quently, the air above the inversion is normally relatively warm and dry. In order to maintain the characteristic discontinuities which appear in the individual soundings near 600 m and 1300 to 2000 m height, an averaging procedure has been devised to preserve these special boundaries. This was achieved by the following method. At first, the top and bottom of the transition layer and the trade inversion were determined in each of the temperature and humidity profiles. Then additional grid points were applied to the different sublayers of each ascent, namely four to the layer 1199 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 1 3 5 between the sea surface and the top of the mixed layer, two to the transition layer, nine to the cloud layer, ten to the inversion and nine to the region between the inversion top and the 700-mb level. If the transition layer could not be detected, its thickness was assumed to be zero. The top of the mixed layer could always be found at all ships and the inversion was present in every sounding obtained on the 'Discoverer' and the 'Planet'. In those 'Meteor' cases during the second period when the inversion was not present, the layer between the top of the transition layer and the 700-mb level was divided into 30 equidistant sublayers. This averaging procedure and the high resolution of the ATEX radiosonde systems allow for a rather detailed description of the structure of the planetary boundary layer as demonstrated in Figure 4. It is interesting to note that the transition layer is marked only by one discontinuity at the top and one at the base while the inversion is clearly subdivided into three parts. The transition between the cloud layer and the inversion is indicated by an isother- mal region with relative small upward decrease in water vapor; in the upper region of the inversion, temperature as well as specific humidity are constant with height. Strong vertical gradients of temperature and humidity form the core of the inversion layer. The vertical thermodynamical structure of the planetary boundary layer as shown in Figure 4 is not merely a statistical result but is present in more than 70% of all soundings obtained in the undisturbed trade-wind regime. Typical deviations from this general picture are commonly observed over the areas of cold upwelling water in the eastern part of the tropical oceans as reported by Reger (1939) and Neiburger et al. (1961). These results could be confirmed by tethered balloon measurements from 'Meteor' in 1965 near Dakar. The profiles of dry- and wet-bulb temperature in Figure 5 indicate the strong downward slope of the inversion layer toward the coast. Furthermore, this example demonstrated that the planetary boundary layer in these regions is normally reduced to the mixed layer and the trade inversion. A very different alteration in the vertical temperature and humidity distributions is often observed at the downstream end of the trade-wind trajectories near the Equato- rial trough and in tropical disturbances in the trades as already noted by Riehl (1954). Here strong convective mixing weakens the layered structure and the trade inversion is often totally absent. Variations of the vertical structure of the thermodynamical properties due to a disturbance, and in the Equatorial trough region (in relation to undisturbed trades), are documented in Figure 6 which shows cross-sections of air temperature, specific humidity, potential temperature and equivalent potential tempe- rature. When the 'Meteor' was moving from North to South, it passed a decaying depression near 23° N and crossed the Equatorial trough at about 11°N. In the de- pression and in the Equatorial trough, the trade inversion was absent. Both regions show a similar increase of water vapor in the lowest 3000 m of the atmosphere. The pronounced minimum of the equivalent potential temperature near the top of the inversion which prevails in undisturbed conditions is not present in the troughs, where increased convection was observed. In these cases no easy definition of the top 1200 136 E. AUGSTEIN ET AL. of the boundary layer can be found, based on the temperature and humidity profiles. The variation of the boundary-layer structure in relation to convection could be observed in more detail during ATEX. From the 'Discoverer' and 'Planet' profiles in Figure 4, one may conclude that in the tradewind area, changes from period one to period two in the vertical distribution of temperature and water vapor were rather height [m] 26.11.1965 9.20 LT 14° 32' N / 19° 2' W 26.11.1965 1741 LT 14° 36' N/ 18°21'W wb 27.11.1965 3.49 LT 14° 33' N/ 17" 37 ' W Fig. 5. Tethered balloon profiles of dry- and wetbulb temperature on an east-west cross-section at the African coast near Dakar. small in spite of the large-scale weather changes. But at 'Meteor' where convection increased during the second phase, distinct differences in the profiles for the two pe- riods can be seen. Here, the trade inversion was not observed in about 40% of the soundings between 13 and 17 February. Therefore, the measurements of this period have been divided further into those with an inversion (dash-dotted) and those without (dashed). Generally, we find an increase of temperature and specific humidity in the entire layer in the second period. At the 'Discoverer' and 'Planet', the transition layer did not move vertically at all while the inversion layer moved downward in the second period (see Figure 4). At the 'Meteor', the transition layer migrated downward and the inversion upward during the second period. This indicates an increase of the depth of the cloud layer with increasing convective activity. And the further downward migration of the transition layer and the destruction of the trade inversion in the dashed profiles (Figure 4) seems to be due to an additional increase of cumulus con- vection. Although the lifting condensation level of surface air need not necessarily be identical with the actual cloud base, we may at least assume that the relative height variations of both are similar. Thus, the cloud base is lowered with enhanced cumulus convection. It is also of interest to notice that the temperature gradient in the cloud 1201 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 137 [m] 32 30 28 26 2U 22 20 18 Fig. 6. North-south cross-sections along 30° longitude of air temperature (°C), specific humidity (g kg-1), potential temperature (K), and equivalent potential temperature (K), (from bottom to top) as measured in August, 1965 by the R.V. 'Meteor'. Inversion base and top: dashed lines. Trough line of a tropical depression at 23° N and the Inter Tropical Convergence Zone at 10°N: dotted. layer decreases with increasing convection and this layer assumes nearly convective neutrality in situations without an inversion. The static stability and convective stability (for classification see: Hess, 1959) of the different layers are represented in Figure 7 by the profiles of virtual potential tempera- ture 9V and equivalent potential temperature 6e, respectively. In addition to the facts already mentioned, we find under undisturbed conditions that 9e decreases slightly up to the inversion base, and rather strongly in the inversion. Above the inversion to 700 mb, the equivalent potential temperature 6e is nearly constant or slightly increasing. 1202 138 E. AUGSTEIN ET AL. CmbJ 700 Ot Fig. 7. The vertical distribution of potential temperatures 9, virtual potential temperature 0V and equivalent potential temperature 6e during ATEX. First period: full lines, second period: dashed lines. Dash-dotted: 'Meteor' profiles in situations without an inversion. When cumulus convection becomes stronger as it did at 'Meteor' during the second period, the minimum at the inversion becomes less pronounced and it nearly vanishes in situations without an inversion (Figure 7, dash-dotted profile). Following Aspli- den's (1971) classification scheme, our undisturbed 9e profiles agree with his modes of depressed convection, and the disturbed profiles with his modes of moderately en- hanced convection. The vertical gradients of 9V and 9e (units °C 100 m_1) within the different layers for all ships and averaged over the observational periods are listed in Table I. In order to investigate changes in sensible heat and total static energy between the first and the second ATEX phases, the differences of potential temperature and equi- valent potential temperature were calculated. By subtracting the values of the second period from those of the first, we obtain in Figure 8 the profiles indicated by solid lines. At 'Meteor' we distinguish again between ascents with (solid line) and without (broken line) an inversion during the second period. In all cases, the integral of A9 between the sea surface and 700 mb is roughly zero. The strongest changes occur in the inversion region. At 'Planet' and 'Discoverer' where the inversion has moved down- ward with time, the warming of the new inversion layer is more or less balanced by cooling of the overlying air up to 700 mb. At 'Meteor' where the inversion is higher in the second phase, the cooling of the old inversion layer is obviously related to a warming of the cloud layer. In cases with no inversion (dashed line), the upper region of the entire layer has become colder and the lower one warmer. If the observations at the northerly ships 'Planet' and 'Discoverer' during both periods and at 'Meteor' during the first period represent undisturbed trade-wind conditions while the second period at 'Meteor' indicate partly weak and partly stronger disturbed conditions, the data suggest that : (aj increasing cumulus convection causes an increase of downward flux of inver- 1203 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER TABLE I 139 The vertical gradients of virtual potential temperature 9V and equivalent potential temperature 6e at the ships 'Planet' (P), 'Discoverer' (D), and 'Meteor' (M). The subscripts 1 and 2 refer to periods 1 and 2. Subscript 3 refers to conditions without an inversion at 'Meteor'. Pi D, M, Pi Da Ms M3 Average Surface layer -0.13 -0.03 -0.43 -0.17 0.00 -0.4? -0.15 -0.19 Mixed layer -0.01 +0.01 -0.07 -0.02 + 0.05 -0.05 -0.02 -0.00 Transition layer +0.45 +0.48 +0.51 +0.22 +0.39 +0.51 + 0.19 +0.39 Cloud layer +0.23 +0.19 + 0.28 +0.22 +0.19 + 0.33 +0.44 +0.27 Inversion layer + 1.86 + 1.74 + 1.38 + 1.72 + 1.3S + 1.07 + 1.53 BOeldz Pi Di Mi P2 D2 M2 M3 Average Surface layer -0.89 -0.62 -1.57 -0.43 -0.81 -1.56 -1.55 -1.06 Mixed layer +0.02 -0.69 -0.15 -0.08 -0.43 -0.08 +0.07 -0.19 Transition layer -3.73 -0.72 -2.82 -2.66 -3.20 -2.14 -2.88 -2.59 Cloud layer -0.01 -0.46 -0.18 -0.32 -0.54 + 0.01 -0.11 -0.23 Inversion layer 1.19 -0.79 1.30 -2.26 -0.98 1.26 1.11 sion air into the cloud layer, thus pushing the inversion upward as suggested by Ball (I960), (a2) this process is combined with downward heat flux which effects a diabatic warming of the cloud layer, (bj strong convective activity destroys the trade inversion; the organized cloud circulation then transports air parcels with relatively low potential temperature upward and with high potential temperature downward, (b2) this process results in a diabatic warming of the lower part of the cloud region and in a diabatic cooling of the upper part. In the planetary boundary layer, the equivalent potential temperature 9e is to a large extent equal to the total static energy of an air mass. We may write : cp0e cpT + gz + Lq where on the right-hand side, the first term represents enthalpy, the second, geopo- tential energy, and the third, latent heat in units of cal g_1. From the curves of the right-hand side of Figure 8, we find that there are only small variations in total static energy in the undisturbed trades at 'Planet' and 'Discoverer'. In contrast to this, the enhanced cumulus convection during the second phase at 'Meteor' is combined with 1204 140 E. AUGSTEIN ET AL. 40 A 6. Cmb] 7no - 800 - 1000 I I I I 0 4 I I I I I 4 0 4 i i i — r-n — n — 4 8 12 16 [°K] Fig. 8. The difference of potential temperature {A9) on the left and equivalent potential temperature (A6e) on the right between the second and the first periods of ATEX. Difference between the second period without an inversion and the first period at 'Meteor' is presented by dashed lines. an increase of total static energy in all layers. Figure 4 indicates that this change is nearly completely due to an increase of water vapor. Since evaporation at the sea surface was smaller in the second period than in the first period, the growth of water- vapor content and thus the static energy must be attributed mainly to the effect of horizontal convergence. The rather constant 0e-value with height in situations without an inversion supports the hypothesis that cumulus convection provides a strong upward transport of water vapor and by this reduces the 0e-minimum in the layer between 800 and 700 mb. 3.2. THE VERTICAL WIND DISTRIBUTION As already noted by Riehl (1954), the atmospheric motion in undisturbed trades below the inversion is characterized by a high degree of wind steadiness S defined as |v| S = = x 100, |v| where |v| denotes the magnitude of the vector resultant wind and |v| the magnitude of the wind speed during the observational period. This steadiness has been supported by a number of observations. As an average for the layer between sea surface and the inversion, Riehl et al. (1951) derived a steadiness of about 90% for a three-month 1205 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 141 period in the northeast trades of the Pacific, and Augstein (1972) found 5 = 96% for a one-month sequence in the Atlantic southeast trades. These values agree fairly well with our ATEX result of 96%. In general, there are only a few sets of detailed boundary-layer wind observations over the tropical oceans. Ship-based measurements have been reported by Reger (1927), Riehl et al. (1951), Augstein (1972), and Holland and Rasmusson (1973). These data are supplemented by pibal, radar, and tethered balloon measurements from small islands by Charnock et al. (1956), Estoque (1971), and De Souza (1972). All these observations, though obtained under different conditions in different geo- graphical regions, have some similar features which are obviously typical for the trades. The average shape of the vertical distribution of wind speed is characterized by a relative maximum in the vicinity of the transition layer. The vertical shear of the wind speed from about 20-m height to this maximum is rather small, with<3|v|/dz^ 10" 3 s-1. The measured changes in wind direction indicate a veering of only 5 to 7 deg below cloud base and up to 1 5 deg in the cloud layer. The wind components at the three ships averaged over the first and the second ATEX period are sketched in Figure 9. Due to the fact that only a few balloons could be tracked below 500-m height, the profiles up to this level are based on the deck-level winds at about 20-m height and the layer-averaged radar wind between the 20-m and the 500-m level. This procedure causes indeed some uncertainties in the wind profile 7.-12.2.1969 13.-17.2.1969 Fig. 9. The mean profiles of the zonal (m) and meridional (v) wind components during the two ATEX periods. 1206 142 E. AUGSTEIN ET AL. below 500 m but does not affect the conclusion that the low-level maximum of both components at all ships lies below the 500-m level. The shape of the profiles at each ship in the planetary boundary layer below 1 500-m height does not vary much between the two periods. But during the whole experiment, latitudinal differences are clearly evident. While the 'Planet' and 'Discoverer' wind components, which are measured at nearly the same latitude, show rather similar height distributions, the southerly 'Meteor' profiles have a different shape, at least above 600 m. Briimmer et al. (1974) have shown that the mean geostrophic surface wind at the center of the ATEX triangle is exactly east-west, while the thermal wind is nearly west, at least up to 500 m. This fact explains the weak vertical shear of the actual wind in the mixed layer. The increasing difference with height of especially the zonal wind component between 'Meteor' and the other ships does not need to be attributed to latitudinal differences. In our case it is due to the vertical slope of the axis of the high pressure cell, which may be an occasional phenomenon. This axis was positioned north of the triangle at the sea surface but had a strong southward slope with height and crossed the triangle at a height between 800 and 700 mb. Consequently, the geostrophic wind at the center of the triangle is rather small but changes its direction remarkably at this level as reported by Briimmer and Augstein (1973). Some detailed information about the low-level wind structure was obtained from special balloons (with an ascent rate of 1 m s_1) which were already tracked from 50 m upward. A series of ten profiles of the u- and ^-components is plotted in Figure 10. Although there are considerable differences between the individual ascents, the shape of the two-day averages coincides rather well with the 'Meteor' profiles in Figure 9. The first low-level maximum lies between 100 and 700 m with respect to the zonal component and between 20 and 450 m with respect to the meridional component. The same features are observed by double-theodolite pibal measurements in the northeast trades near Bimini, Bahamas, as shown in Figure 11. These ascents are typical for the whole data set. Two facts are of special interest, namely the remarkable small-scale variations below the 1100-m level (inversion height) and the relatively small time changes of the large-scale wind field. The relatively constant u and v values of the averaged data in the mixed layer, which coincide with the ATEX findings, imply an excellent mixing of momentum throughout the subcloud region. Thus, in this part of the trade-wind planetary boundary layer, the mean vertical distributions of horizontal momentum, sensible heat and water vapor are nearly constant with height. This observational result supports the hypothesis that the vertical turbulent fluxes of the above mentioned quantities through the mixed layer which were estimated from budget calculations (Augstein et al., 1973; Holland and Rasmusson, 1973) can hardly be achieved by micro-scale turbulence. It seems much more probable that convective processes, such as those described by Frisch and Businger (1973), are mostly respons- ible for the momentum as well as the sensible and latent heat fluxes. 1207 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 143 During the last 50 years, several hypotheses about the formation and the mainte- nance of the layered structure of the planetary boundary layer in the trades have been discussed but no satisfactory theory has been developed. While von Ficker (1936b) erroneously assumed that the trade inversion separates two different air masses, Riehl et al. (1951) showed that for dynamical reasons, air from above must sink through the trade inversion into the cloud layer. The BOM EX and ATEX measurements, discussed by Holland and Rasmusson (1973) and Augstein et al. (1973), respectively, have clearly 17.2. Height Cm] 1500 - 1000 - 500 11 14 1707 1755 23 33 18.2. 19.2. 4 58 7 32 1701 1921 210 513 1500 1000 - 500 Tl \ -2 Fig. 10. Zonal (//) and meridional (») wind components of special low-level soundings at 'Meteor'. proven that the large-scale sinking has even a maximum of about 500 m day-1 at the inversion level and extends to the sea surface. Consequently, the stable layers in the planetary boundary layer cannot be regarded as solid with respect to the vertical mass transports, at least on the large scales of atmospheric motion. But as the discon- tinuities in temperature and humidity oscillate around specified height ranges in a permanent divergent air flow, further processes must be assumed in order to balance 1208 144 E. AUGSTEIN ET AL. . v — w- \^' -•• *:*-..s» 5 © " o i r s 1209 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 145 the large-scale subsidence. Malkus (1958) suggested that the structure of the trade- wind moist layer seems to be the effect of a delicate balance of different physical pro- cesses on various scales of motion. Augstein (1972) has developed a qualitative scheme, Figure 12, which is in basic agreement with observations. This concept implies that mainly four processes are important in the structure of the boundary layer, namely, large-scale subsidence which extends from the top of the inversion down to the sea surface, mechanical turbulence in the surface layer, dry convection in the mixed layer cloud layer stable transition layer mixed layer unstable boundary layer turbulence mean subsid. horiz div. 30 3t 3q at 30 at 3q at 30 3t 3q at 4 i c i <0 >o >0 <0 ^0 ^ 0 [ ) >0 > 0 >0 >0 <0 0 > 0 <0 <0 <0 > i Ir- i 1 i \ II B ^0 fe 0 >0 >0 <0 <0 \ • 2*0 > 0 >0 >0 <0 < 0 Mechanism of vertical transports in the lower trade winds A: mechanical turbulence C: cumulus convection B: dry convection D: mean subsidence Fig. 12. A scheme of the main vertical transport processes in the trade-wind planetary boundary layer and their qualitative effects on the local variations of potential temperature and specific humidity (after Augstein, 1972). and cumulus convection in the cloud layer. The combined effect of all of them generates and maintains the vertical structure of the lower trade-wind region. As a consequence of this assumption, time variations of the vertical structure of the planetary boundary layer are due to changes of one or more of the above mentioned processes. In Figures 13 and 14, the time series of the top and base of the inversion and the top of the mixed layer are plotted for the anchor station of 'Meteor' 1965 at the Equator and for the corner ships of the ATEX triangle. All graphs show coinci- dently remarkable height changes of all boundaries. The amplitudes of short-term vertical motions (such as several hours) are of the same magnitude as long-term oscilla- tions of several days. 1210 146 E. AUGSTEIN ET AL. [ml 2 500 1500 - 500 -■ "Jl '"Ml 1 ' .1 ! i i/ 1 1 , ■i >i t • l/'i i H ij I «•! 1 1 ■ ■ . i Iliii 1" ' 1 « .' 'j'M Vi * n ifj» i • -1 — I — I — I- ■i 1 1 1 1 1— I 1—1 1- 16 17 18 19 20 21 22 23 24 25 26 27 28. 29 30 1 2 3 4 SEPTEMBER 1965 OCTOBER 1965 Fig. 13. Height variations of the base (full line) and top (dashed line) of the trade inversion and the top of the mixed layer (dash-dotted) during an anchor-station period at the intersection of 30° W longitude and the Equator in the SE trades. In spite of some uncertainties in short periodic variations, we find that the inversion base and top are generally displaced in a similar fashion. Therefore, considering time changes, no dependency exists between height and thickness of the inversion. Like- wise, the differences for potential temperature and specific humidity between the base and top of the inversion or transition layer are not correlated with the height of the layer itself. Regarding spatial relations between height and thickness of the inversion, we find, in agreement with the results of von Ficker (1936b) and Riehl et al. (1951), that with increasing inversion height downstream of the trade-wind trajectory, 89 and Sq decrease. The average ATEX values, when 'Planet' occupied the most upstream and 'Meteor' presumably the most downstream position, are given in Table II. Some details about the time variations of the different sublayers of the trade-wind planetary boundary layer may be obtained from a three-day series of soundings in the Atlantic southeast trades in Figure 15. The base of the trade inversion is indicated in the temperature profiles by the dash-dotted line. The transition layer and the inversion are particularly clearly established in the specific humidity distribution (lower curves) 1211 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 147 HEIGHT [m] DISCOVERER A 2000 - ' 1 * j \ 'it : / r. ' W/r Vj i! i'i V 11 "k '* i \ n ii ! 1 i f M/lifra N Ml il i"m * i 1' I / uf 1 \ f * / ?'VP; l \ N t 1 1 IV 1000 - 1 l\ I \l\i\ /\ J 1/ • • ■•''■'" V;;' u,jV ': ? V A 1 -rj 1 : 1 1 1 1 1 1 I 1 1 i i i i i 1 1 1 1 1 — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — r 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 FEBRUARY 1969 Fig. 14. Height variations of the base (full line) and top (dashed line) of the inversion and the top of the mixed layer (dotted) at the ATEX-ships in the NE trades. 1212 148 E. AUGSTEIN ET AL. TABLE II The mean height of the inversion base h(h) and inversion thickness Sz in wand the difference of potential temperature SO in K and specific hu- midity Sq in gg^1 between inversion base and top during ATEX, 1969. 'Planet' 'Discoverer' 'Meteor' h (/&) 1198 1337 1427 Sz 401 435 393 se -8.9 -8.6 -5.4 Sq 6.2 4.6 4.6 mbl 12 3 4 5 6 7 6 9 12 13 U 15 16 17 18 19 20 i 1 22 23 24 400 • \ V \^ \\ \\v \ \ \ \ \ V \ 500 ' VV \ \ V\V\ NX\ 600 ■ \\\\ < a\\\ 700 - k\\\\ \\V\\ T \u\ -S^ W\\\\ 900 - 1000 - > On WW 0 n \ WW Fig. 15. A series of temperature (D and specific humidity (q) profiles at the anchor station 1965 from the 27-29 of September (Equator/30o W). but can also be detected in the temperature profiles (upper curves). This example shows that although there are considerable time variations in the vertical structure of each layer, these variations do not lead to the destruction of the layers themselves. There- fore, not only the trade inversion but also the other layers may be regarded as perma- nent features of an undisturbed trade-wind atmosphere. 4. Final Remarks The preceding presentation concentrates on the description of the lower part of the marine atmosphere over the tropical oceans and is based on observations. These data may serve as guidelines in the development of theoretical models of the planetary boundary layer in low latitudes. 1213 THE VERTICAL STRUCTURE OF THE ATMOSPHERIC PLANETARY BOUNDARY LAYER 149 A satisfactory discussion of the observed variations of the vertical structure must include a simultaneous study of the relevant physical processes, a topic beyond the goal of this paper. Acknowledgements The expeditions and the post experimental work were sponsored by the 'Deutsche Forschungsgemeinschaft, (German Science Foundation). We are most indebted to Prof. K. Brocks, the coordinator of both expeditions, the Atlantic Expedition, 1965 (IQSY) and the Atlantic Tradewind Experiment, 1969 (ATEX), whose untiring effort and personal engagement contributed so much to the success of this work. References Aspliden, C. I.: 1971, On Energy Distribution in the Tropical Troposphere, Ph. D. Dissertation, Florida State University, Tallahassee, 1-232. Augstein, E.: 1972, 'Mass and Heat Budget Estimations of the Atlantic SE Trade Wind Flow at the Equator', ' Meteor '-Forschungsergebnisse, B, No. 8, Borntrager Verlag, Berlin, 31-41. Augstein, E., Riehl, H., Ostapoff, F., and Wagner, V.: 1973, 'Mass and Energy Transports in an Undisturbed Atlantic Trade Wind Flow', Mon. Weather Rev. 101, 101-111. Ball, F.K. : 1960, 'Control of Inversion Height by Surface Heating', Quart. J. Roy. Meteorol. Soc. 86, 483^194. Betts, A. K.: 1973, 'Non-Precipitating Cumulus Convection and its Parameterization', Quart. J. Roy. Meteorol. Soc. 99, 178-196. Brocks, K.., 1970: 'Reisebericht der Atlantischen Expedition 1965 (IQSY) mit dem Forschungsschiff "Meteor"', 'Meteor' Forschungs Ergebnisse, A, No. 8, Borntrager Verlag, Berlin, 18^t2. Brocks, K.: 1972, 'Die Atlantische Expedition 1969 (GARP) mit dem Atlantischen Passatexperiment (APEX)', Meteor-Forschungs Ergebnisse, A, No. 9, 1-30. Briimmer, B. and Augstein, E. : 1973, 'Large-Scale Dynamic Relations in the Lower Layers of the Atlantic Trade Winds During ATEX', Paper presented at Technical Conference on Hurricanes and Tropical Meteorology, May 14-17, 1973, Key Biscayne, Florida. Briimmer, B., Ostapoff, F.. and Schmidt, H.: 1973, Upperair Soundings During ATEX, NOAA Publication, Miami, Florida. Briimmer, B., Augstein, E., and Riehl, H. : 1974, 'On the Low Level Wind Structure in the Atlantic Trade', Quart. J. Roy. Meteorol. Soc. (accepted for publ.). Bunker, A. F., Haurwitz, B., Malkus, J. S., and Stommel, H.: 1950, 'Vertical distribution of Tempe- rature and Humidity over the Caribbean Sea', Papers in Phys. Oceanogr. and Meteorol., Mass. Inst. Tech. and Woods Hole Oceanogr. Inst., No. 11, pp. 1-82. Charnock, H., Francis, J. R. D., and Sheppard, P. A.: 1956, 'An Investigation of Wind Structure in the Trades: Anegada 1953', Phil. Trans. Roy. Soc. London, Series A, 249, 179-234. Deardorff, J. W. : 1972, 'Numerical Investigation of Neutral and Unstable Planetary Boundary Layers', /. Atmos. Sci. 29, 91-1 15. De Souza, R. L. : 1972, A Study of Atmospheric Flow over a Tropical Island, Ph. D. Dissertation, The Florida State University, Dept, of Meteorology, 1-204. Estoque, M. A.: 1971, 'The Planetary Boundary Layer over Christmas Island', Mon. Weather Rev. 99,193-201. Ficker, H. von: 1936a, Bemerkungen iiber den Warmeumsatz innerhalb der Passatzirkulation, Verlag Akad. Wissenschaften, Berlin, Germany. Ficker, H. von: 1936b, Die Passatinversion, Veroffentlichungen des Meteorologischen Institutes de Universitat Berlin, 1-33. Frisch, A. S. and Businger, J. A.: 1973, 'A Study of Convective Elements in the Atmospheric Surface Layer', Boundary-Layer Meteorol. 3, 301-328. Garstang, M. 1972: 'A Review of Hurricane and Tropical Meteorology', Bull. Am. Meteorol: Soc. 53, 612-630. 1214 1 50 E. AUGSTEIN ET AL. Hess, S. L.: 1959, Introduction to Theoretical Meteorology, Holt, Rinehart and Winston, New York, 362 pp. Holland, J. Z. and Rasmusson, E. M. : 1973, 'Measurements of Atmospheric Mass, Energy and Momentum Budgets over a 500-kilometer Square of Tropical Ocean', Mon. Weather Rev. 101, 11-55. Malkus, J. S. : 1958, 'On the Structure of the Trade Wind Moist Layer', Paper in Phys. Oceanogr. and Meteorol., Mass. Inst. Tech. and Woods Hole Oceanogr. Inst., No. 13, 1-48. Neiburger, M., Johnson, D. S., and Chien, C. W.: 1961, 'Studies of the Structure of the Atmosphere over the Eastern Pacific Ocean in Summer, F, The inversion over the Eastern North Pacific Ocean, Univ. Calif. Press, Berkeley, 94 pp. Nitta, T. and Esbensen, S. : 1973, 'Heat and Moisture Budget Analysis Using BOMEX Data', Mon. Weather Rev. (submitted). Reger, J.: 1927, 'Der Sudostpassat', Beitrage zur Physik der freien Atmosphare 13, 59-63. Reger, J.: 1939, 'Der statische Aufbau der Luft iiber dem Sudatlantischen Ozean', Wiss. Ergebn. dtsch. Atl. Exped. 'Meteor* 1925-27 16, 1-63. Riehl, H. : 1954, Tropical Meteorology, McGraw Hill Book Co., New York, 392 pp. Riehl, H., Yeh. C, Malkus, J. S., and LaSeur, N. E.: 1951, 'The North-East Trade of the Pacific Ocean', Quart. J. Roy. Meteorol. Soc. 11, 598-626. Tennekes, H.: 1973, 'A Model for the Dynamics of the Inversion above a Convective Boundary Layer', J. Atmos. Sci. 30, 558-567. 1215 594 JOURNAL OF PHYSICAL OCEANOGRAPHY Volume 4 The Detection by ERTS-1 of Wind-Induced Ocean Surface Features in the Lee of the Antilles Islands Richard Cram and Kirby Hanson1 Rosenstiel School oi Marine and Atmospheric Sciences, University of Miami, Coral Gables, Fla. 33124 (Manuscript received 31 January 1974, in revised form 18 April 1974) ABSTRACT Photographic data received from the ERTS-1 satellite over the Lesser Antilles Islands show distinct ocean features on the leeward side of each island. Attempts to relate these features to ocean eddy formations with the aid of ground truth data proved unsuccessful. However, surface and upper air wind data indicate a good correlation with the size, shape, and downwind extent of the ocean features. Studies to date indicate strongly that these features result from horizontal differences in sea surface roughness due to the wind-shadow effect of the islands. The results suggest that horizontal variations in the reflectance of the sea surface will make remote sensing of the ocean mixed layer more difficult than previously anticipated. The surface reflection seems to be large enough to mask the smaller variations in backscattered energy from the mixed layer. Efforts to limit the effect of surface reflectance by photo- graphic differencing of two multi-spectral scanner bands were unsuccessful. 1. Background Investigations near Johnston Atoll by Barkley (1972) have shown that sufficient current flow produces a wake dominated by eddies on the leeward side of the island. Eddies with a cyclonic rotation bring deep water to the surface and, if the water is rich in nutrients, it could contribute significantly to the productivity of the area. An example of this form of productivity enhancement was detected during a fishery oceanography survey of the eastern Caribbean near St. Vincent Island. Ingham and Mahnken (1966) found that tuna schools and bird flocks were concentrated in an area west of this Lesser Antilles island. They also noted that plankton and pri- mary productivity in the mixed layer were higher in this area than the Atlantic, and that oceanographic data revealed the existence of horizontal temperature differences in the upper thermocline which might indi- cate the presence of eddy-like features in the ocean. They suggested the possibility that the increased pro- ductivity of this area is a consequence of downstream turbulence on the Caribbean side of St. Vincent Island. Because of the capability of the ERTS-1 camera system to simultaneously view the same area through several different band pass filters, it was anticipated that ocean features similar to those mentioned above could be detected and monitored by the satellite. Although several ocean features were observed by ERTS-1 in the lee of the Lesser Antilles Island Arc, 1 Present affiliation : Atlantic Oceanographic and Meteorological Laboratories, NOAA, Miami, Fla. comparisons with ground truth data analyses by Hanson el al. (1973) showed that the features were not associated with eddv-like formations. 2. ERTS-1 data enhancement ERTS-1, launched in July 1972, collected six MSS (multi-spectral scanner) data sets over the Lesser Antilles region from September 1972— April 1973, when a recording system failure caused the termination of data collection in that area. ERTS coverage in the four MSS bands was obtained for the following dates; 26 September, 13-14 October, 1 November, 19 No- vember, 1972, and 17 February and 24 March, 1973. The satellite pass over the Lesser Antilles area occurs at approximately 1400 GMT. Each of these data sets indicates ocean surface features on the leeward side of many of the islands. They appear as areas of lower photo density in the ERTS-1 images. Five of the data sets are presented in Figs. 2-6. The sixth MSS data set, collected on 1 November, is not included due to extensive cloudiness over the Antilles Arc; the only relatively clear area is west of Guadeloupe. Several techniques to enhance the lower density range of the ERTS-1 positive transparencies have been studied. Density slicing of the ERTS-1 images through the use of a color densitometer was investigated. The densitometer allowed the assignment of up to 32 different colors to selected portions of the density range of the transparency, producing a false color image. 1216 October 1974 RICHARD CRAM AND KIRBY HANSON 595 MSS 4 MSS 5 MSS 6 MSS 7 Fig. 1. 13-14 October 1972 ERTS coverage of the Lesser Antilles: MSS bands 4-7. Several attempts to enhance the lower photo density range did not improve the features seen in the ERTS-1 transparencies. Other tests with multi-spectral viewers, designed specifically to view transparencies produced from narrow band energies, have indicated that near- coastal or shallow water regions may readily be en- hanced, but little success has been achieved in enhancing density differences across deep ocean features such as those in the lee of the Lesser Antilles. The most effective photographic rendition of oceanic features is achieved by simple contact printing of the ERTS-1 positive transparencies, and arranging a spatial 62°W 60°W 60°W MSS5 WINDS Fig. 2. 26 September 1972 ERTS coverage of the Lesser Antilles: MSS band 5. 1217 596 JOURNAL OF PHYSICAL OCEANOGRAPHY 62eW 60°W 62°W Volume 4 60°W 16°N ~ RADIOSONDE mb 7001 q 8S0 n. knots — I000O n SHIP DATA 3 WAVE (ft) 2 1 3 SWELL (It). 14°N 12°N - WINDS MSS 5 Fig. 3. 13-14 October 1972 ERTS coverage of the Lesser Antilles: MSS band 5. composite of the resulting negative prints. In this way the darker features in the lee of the islands show up as lighter areas which seem to bring out small changes in lower density. Fig. 1 is a mosaic of negative prints for 13-14 October in each of the four MSS bands : ERTS band MSS 4 MSS 5 MSS 6 MSS 7 A (Mm) 0.5-0.6 0.6-O.7 0.7-0.8 0.8-1.1 MSS 5 seems to have the optimum sensitivity for de- tecting these ocean features. The changes in photo density are much more clearly defined in MSS 5 than they are in MSS 4 and slightly clearer than MSS 6 and MSS 7. 3. ERTS-1 data interpretation a. ERTS photographic data Fig. 2 shows the ERTS-1 coverage of the area west of Martinique. Although much of the region is covered with cirrus and small cumulus clouds, two lighter areas are visible near the top of the print. A narrow line ex- tends to the southwest in the lee of the northern tip of Martinique. Another light feature can be seen at the top edge of the negative print to the northwest of Martinique which also extends in a southwest direction parallel with the feature at the northern tip of the island. This feature appears to be originating from the western side of Dominica. Figs. 3 and 4 show the data received for the 13-14 October and 19 November orbits, respectively. In the October data, bright areas can be seen to the west of all the islands from Guadeloupe to Grenada and Tobago. The brightest area is to the west of St. Vincent. The features extend in a west to west-northwest direc- tion away from each island. On 19 November, only moderate indications of ocean features are evident. These features extend slightly south of west in the lee of Martinique, St. Lucia and Grenada. The longitudinal extent of the 19 November features is much smaller than in the other cases. One explanation for the dimin- ished size of these ocean features is given in Section 3b. Figs. 5 and 6 show the remaining ERTS-1 data collected near the Lesser Antilles Islands. On 17 February 1973, bright areas in the negative prints can be seen to the west of each island from Guadeloupe to St. Vincent even though several clouds are present. The features in this case extend slightly north of west 1218 October 1974 RICHARD CRAM AND KIRBY HANSON 62°W 60°W 62°W 597 60°W I6°N - 14°N - 12°N - WAVf (<>) St—«i < SWEU{f>) - 0 - VI |0 (1 v » S £ sr* 0 ~ k*/ *> MSS 5 WINDS Fig. 4. 19 November 1972 ERTS coverage of the Lesser Antilles: MSS band 5. as opposed to the component south of west noticed on 26 September and 19 November. Similarly, on 24 March very bright features are seen on the leeward side of the island arc. These features have a component further north of west than that seen on 13-14 October or 17 February. b. Witul and topography The winds for each area displayed in Figs. 2-6 were averaged to obtain a mean speed and direction for the region. The estimated direction of each ocean feature was also determined by measuring the angle between a meridian and a line drawn through the center of each feature. An average angle was calculated for each day. The resulting correlation between the wind and the direction of the ocean features is given in Table 1. It can be readily seen from the table that the direc- tions of the wind and ocean features are in agreement within a few degrees. Clearly, the winds and the ocean features detected by the ERTS-1 satellite are directly related. It is also suggested in Table 1 that wind speeds between 10 and 15 kt produce very well defined features on the leeward side of the islands while speeds near 20 kt greatly diminish the size and sharpness of the features as shown, for example, in the 19 November results. Duntley (1964) and others have shown that the in- tensity of reflected light from the ocean surface varies with solar zenith angle as well as wind speed. For high solar zenith angles (20°) the intensity of red light varies most rapidly with low wind speeds (3 to 13 kt); the opposite effect is seen for medium and low solar zenith angles, with the greatest change in intensity occurring at wind speeds > 20 kt. At first glance, Duntley's work would seem to be contrary to the evidence presented in Table 1, where the 19 November data, with higher wind speeds and medium solar zenith angle (43°), show only a slight indication of ocean features, while the 17 February data with slower wind speeds but the same solar zenith angle show very distinct features. The apparent inverse relationship between wind speed and feature size and clarity is most likely caused by the topography of each island, i.e., it appears that the height and orientation of the islands block the air flow most effectively when wind speeds are below 15 kt. At speeds greater than 15 kt the islands seem to lose their effectiveness to retard the wind; wave forms within the island wake become similar to those in un- protected areas. Thus, the intensity of reflected energy is nearly the same and only slight contrasts are produced in the ERTS-1 negative prints. 1219 598 JOURNAL OF PHYSICAL OCEANOGRAPHY 62°W 60°W 62°W Volume 4 60°W 16°N _ 14°N - 12°N _ MSS5 WINDS Fig. 5. 17 February 1973 ERTS coverage of the Lesser Antilles: MSS band 5. The Lesser Antilles are volcanic islands and therefore very mountainous with only a few low, relatively flat areas. Guadeloupe, Dominica, St. Lucia, St. Vincent and Grenada have mountain ranges extending north- south with heights above 1000 m on most islands. When the wind is nearly perpendicular to the mountain ranges, the ocean features have almost the same width as the islands. However, when the wind direction is at an acute angle to the north-south mountain ranges, as in the 26 September case, the ocean features become more narrow. Furthermore, Martinique, which has mountains at its northern end over 1300 m and rela- tively low terrain under 500 m at the southern end, causes the ocean feature to be only as wide as the northern half of the island, even when the wind is perpendicular to the mountains. Further evidence that the influence of topography on the air flow is the main cause of these ocean features can be seen by studying the area in the ERTS-1 prints to the west of Barbados. Barbados is a relatively flat island; its highest peak is approximately 400 m. The ERTS-1 orbits of 13 October and 24 March pass sufficiently close to Barbados so that any ocean feature extending from that island would be seen on the eastern edge of the ERTS-1 image. However, there is no feature visible in either ERTS-1 print, suggesting that the topography of Barbados is too low to produce an extensive wind-induced feature on its leeward side. c. Surface reflectance It is apparent from the ERTS-1 data that changes in wind speed greatly affect the amount of backscat- tered energy due to the variation in surface roughness. As a result, it appears that remote sensing of the mixed layer will be more difficult than previously anticipated because the energy reflected from the ocean surface must be taken into account. Since the ERTS-1 multi- spectral scanner senses the same area in four separate energy bands at the same time, it may be possible to minimize in the data the effect of energy reflected from the surface by taking energy differences between two spectral bands. Thus, the difference between bands 4 and 7, for example, would be more representative of the energy reflected from below the ocean surface. By superimposing two ERTS-1 transparencies, one a positive and the other a negative, the energy reflected from the surface would be minimized and the resulting image would tend to enhance the radiation back- scattered from the subsurface. This photographic differencing technique was employed in an attempt to detect changes in the backscattered energy patterns, indicative of subsurface eddy formations. Unfortu- 1220 October 1974 RICHARD CRAM AND KIRBY HANSON 62°W 60°W 62°W 599 60°W 16°N — 14°N — 12°N MSS5 WINDS Fig. 6. 24 March 1973 ERTS coverage of the Lesser Antilles: MSS band 5. nately, there was no noticeable change in the pattern after applying this method to the 13-14 October data. More research in the area of minimizing the energy re- flected from the ocean surface is needed before the detection of subsurface features can be achieved from satellite height. 4. Conclusions The results of studies with ERTS-1 photographic data of the Lesser Antilles Island Arc have shown that changes in sea state have a large effect on the amount of backscattered solar radiation reaching a satellite sensor. Smoother seas cause a decrease in the energy reflected from the ocean surface. This is immediately Table 1. Observed wind speeds and directions and estimated direction of ocean surface features in the lee of the Antilles Islands. 26 Sept. U Oct. Date 14 Oct. 19 Nov. 17 Feb. 24 Mar.* Wind speed 10 Wind direction 60° Estimated direction 57° of ocean features 10 13 110° 103° 105° 101° 19 85° 12 10 99° 116° 102° 114° * The mean wind for 24 March does not include the two ship reports southwest of Barbados which are due to local weather conditions. apparent from the negative ERTS-1 prints (Figs. 1-6) which display much lower photo densities in the wind shadow of each island than in the open ocean, un- protected from the wind. It is evident from this study that horizontal variations in the reflectance of the sea surface will make remote sensing of the ocean mixed layer more difficult. Preliminary attempts to remove the surface reflec- tance by photographic differences have not yielded positive results. Further studies are needed to produce a method to minimize the effect of surface reflectance and qualitatively describe horizontal variations in particles in the ocean mixed layer through remote sensing. Acknowledgments. This study was supported by NASA Contract S-70246AG-1, Earth Resources Technology Satellite Program, and by NOAA Contract 04-3-022-12, Analysis of ERTS-A Satellite Photos. REFERENCES Barkley, R. A., 1972: Johnston Atoll's wake. J. Marine Res., 30, 201-216. Clarke, G. L., G. C. Ewing and C. J. Lorenzen, 1970: Spectra of back-scattered light from the ,sea obtained from aircraft as a measure of chlorophyll concentration. Science, 167, 1119-1121. 1221 600 JOURNAL OF PHYSICAL OCEANOGRAPHY Volume 4 Duntley, S. Q., 1964: Oceanography from manned satellites by report. Contrib. No. 42, Tropical Atlantic Biological Lab- means of visible light. Oceanography from Space, Woods Hole oratory, Bureau of Commercial Fisheries, Miami. Oceanographic Institution, 39-45. jerloVj N G 196g. optical Oceanography. Amsterdam, Elsevier, Hanson, K. J., F. Hebard and R. Cram, 1973: Oceanographic 194 pp features in the lee of the Windward and Leeward Islands: ERTS and ship data. Proc. Symp. Significant Results Ob- Maul> G- A> 1973 : Applications of ERTS data to oceanography tainedfrom the Earth Resources Technology Saiellite-1, Vol. 1, and the marme environment. NOAA/AOML, Miami. NASA SP-327, 1357—1363. Ross, D. S., 1969: Color enhancement for ocean cartography. Ingham, M. C, and C. V. W. Mahnken, 1966: Turbulence and Oceans From Space, P. C. Badgley, L. Miloy and L. Childs, productivity near St. Vincent Island, B. W. I. : A preliminary Eds., Houston, Gulf Publ. Co., 50-63. 1222 Comments on the Quality of the NWS Pyranometer Network Data FROM 1954 TO THE PRESENT Kirby J. Hanson National Oceanic and Atmospheric Administration Miami, Florida 1. BACKGROUND These brief comments on the quality of past National Weather Service (NWS) pyranometer data must be prefaced with a clear statement that very little is known about the quality of the data. The principal documentation is (1) the calibration procedure by MacDonald and Foster (1954); (2) a field survey of selected sensors by Flowers and Starke (1967); (3) description of the instruments and method for calibrating field instruments by Hill (1966); (4) a review of the field instrument calibrations from 1954-1972 by Hanson et al. (1973); and (5) an examination of some field sen- sor degradations by Case (1973). For discussion we will consider two types of errors: systematic and random. However, in or- der to describe the systematic errors of the NWS pyranometer data set, it is necessary to include an indication of the absolute calibration level of NWS pyranometer standards relative to the var- ious pyrheliometric scales. The recent paper -by Frohlich (1973) has clar- ified much of the confusion on pyrheliometric scales that existed in the past few years. The result of Frohlich' s work is shown in figure 1. We have used the separation of scales in figure 1 to shown in figure 2 the level of NWS standards. Pyrheliometer standard No. EA2273, which is the primary standard of the NWS, is shown at -0.5 percent lower than the IPS 1956 level based on IPC III. NWS primary pyranometer standard No. 1973 has been shown by Hanson et al. (1973) to be 3.5 percent higher than EA2273. Thus, the NWS primary pyranometer No. 1973 appears to be between the present Absolute Scale and the Smith- sonian Scale of 1913. The following corrections would have to be applied to NWS pyranometer data in order to correct the data to the indicated scales. SO SI S (IPC 1 I9S9) 3«it*«ofttwi I Scat* r«*is«d£ ■ • •• ■■ *0 SI 12 (Poltdom 1932/94) „„ ^ ■' *.,/•• v> -■' 1 i_- 'M SO Si 14 (T««o««o 19*3/70) "* r i ♦ 3.21.4 l ♦9J t.S ♦ 4J ±.6 I ♦4.7 t .3 \ i -4«*.t ' -2.3 *.4 : II _ «MTCRFLOW(Tokl« M»«»tol» 1932/32) ~3 WILLSON (Tckl* Mualm I998/72) lllllull - ' * ■-; 5 ■ fc«it - i*" P4CKA0IIPC III 1970. 0««**I972) ■ ■ - ... — ... ■ MBS (IPC III 1970) TIKOWALOT 10..M I9J0) ! t IS«*(IPe III 1970) . k*0« 13 1 lit ±v Wm*> »M *.» ' 1 1.7 ±.2 ♦0.9 1.2' \ ¥»Z SO T7 (IPC III 1970) ±4 1 f-I.S 10 7-1.3 t.O IPS I9S« t, 210 (IPC III 1970) (IPC III 1970) 1 1 -OS 1.1 ' ' -03 S I 210 (Dk.o. 1934) , *" ' • IS! (IPC HI 1970-13%) iff i«»us " ' ■ « •_jj 1 149 (T*r*ni« 1933/39) mmam ____ Figure 1. Surnary of ccnparisoris of the Radiometric Scales since 1930. The IPS values are referenced to IPC III 1970 (after Frolich, 1973). 1223 Scale Correction to NWS Data 1957-1972 (percent) 1. Smithsonian Scale 1913 +0.8 to +1.6 2. IPS 1956 (based on): a. Smithsonian Standards -0.4 to -1.2 b. Angstrom Standard (No. 210, IPC III) -3.0 3. Absolute Scale -0.8 to -1.4 4. Angstrom Scale 1905 -3.3 to -3.8 2. ERROR SOURCES With the limited information available on the performance for NWS field pyranometers during the period 1954-present, it is not possible to perform an error analysis. However, it is possi- ble to be specific in some areas and make esti- mates in others in order to provide a preliminary indication of probable errors in the entire data set. Such an indication is given in table 1. Rtlotix Seal* (p*rct*t) Smithiomon Scolt «•«.»•« 1913 Wk Abtoivtt Scot* WML. IPS.I9J6IIPC m>- injuiom scon r M NWS Primary Pyrflftomtti Slomlora No. 1973 -NWS Pr.mory Pyrhtliomcle Slondord C& 7273 Figure 2. Radiometric scales (after Frohlich, 1973) and NWS standards. 2.1 Systematic Errors The absolute accuracy of the NWS data de- pends on standardization of the instruments to the true radiation scale. Unfortunately, as pre- viously indicated, the true radiation scale has not been determined from the existing scales. However, recent advances in technology suggest that the Absolute Scale is probably closest to the true scale. Thus, in table 1, a systematic error is determined based on the departure of the NWS primary standard pyranometer from the Absolute Scale. Another systematic error is presented due to crossmatching of sensor surfaces on calibra- tion of field pyranoaeters in the Integrating sphere. The data in table 2 show the sensitiv- ities of working standard pyranometers as deter- mined (1) in the integrating sphere and (2) in the sun, by comparison with the lamp black, pri- mary standard No. 1973. The working standards are of two types: lamp black,, and Parsons black. The lamp black working standard (No. 1977) shows no difference in sensitivity determined by these two methods. However, the Parsons black stand- ards indicate about 7 percent lower sensitivities in the sphere. When these two types of working standards were used to calibrate field pyranome- ters, the result was that about 50 percent of the field instruments had sensitivities determined 7 percent too low (thus radiation measurements with the instrument would be 7 percent too high) and 50 percent of the instruments had no systematic error. The first case was associated with a Par- sons black working standard and a lamp black field instrument. The second resulted from matching of sensor surfaces. Since records on the pre-deploy- ment calibrations and the type of sensor surface is known it may be possible (with some effort) to compensate for this effect. Table 1. Solar Irradiance Error Estimate for NWS Pyranometer Network, 19S4-1972 INSTRUMENT a. Standardization to Absolute Scale b. Reproducibility of Standard- ization *c. Crossmatching on Standardlza- Error (percent) Systematic Random tlon ♦7 and 0 d. Temperature Responae +1 2.5 e. Cosine and Azimuth Responae 3 f. Linearity 1 8- Degradation' with Time 3 2. INSTRUMENT EXPOSURE a. Incomplete Field of View 1 b. Frost, Dew, etc. 1 3. RECORDING SYSTEM a. Standardization 0.3 b. Stability 1 4. DATA a. PROCESSING Integration (Visual) compensated for at individual 2 +2 to locations f9 5.8 •Can be A final systematic error is given for tem- perature response. This is based on the fact that all calibrations in the sphere are done at about 27°C; whereas, the average temperature over the U.S. network is considerably less, probably near 10°C. For this calculation, a temperature coefficient of -0.1 percent/°C was assumed. 32 1224 Table 2. Sensitivities of NWS Working Standard Pyrar.ometers Determined by Comparison with Primary Standcu-d Purarxorr.eter No. 197Z- (Sensitivities are In nv/cal cm" Bin" ) 2.2 Random Errors Lamp Black Surfaca Parsons Black Surface Working Standard Pyranometer No. 1977 5425 5426 1811 Sensitivity Determined by Comparison with (lamp black) Primary Standard No. 1973 a) In Integrating Sphere 2.72 2.39 2.23 2.68 b) In Sun 2.72 2.58 2.38 2.89 Sphere minus Sun Value 01 -7.4 X -6.3 X -7.3 X There are many factors which determine the assessment of random errors. These are discussed by the WMO (1971) and by Latimer (1971). Nicolet (1948) suggests that 5 percent error represents "good and careful work." Latimer (1971) suggests an error of about 5 percent for the type of in- struments used in the NWS pyranometer network. The error estimates given in table 1 suggest • systematic error of +2 percent for roughly half the NWS calibrated instruments and +9 percent for the other half. In addition, by the law of prop- agation of independent errors, an error of about 5.8 percent might be assumed as representative of the error resulting from the combined random mea- surement sources. Frohlich, C. (1973): Absolute radiometry and the international pyrheliometric scale of 1956. Presented at CIMO VI, Helsinki, 1973. Hanson, K. , J. Hickey, and W. Scholes (1973): A report on the pyranometer calibration program of the U.S. Weather Bureau, ESSA, and NOAA, 1954-72. To be published as an ERL/NOAA Technical Report. Hill, A. (1966): Calibration of solar radiation equipment in the U.S. Weather Bureau. Solar Energy, 10(4). Latimer, J. (1971): Radiation Measurements , IFYGL, Tech. Manual Series, No. 2, NRC Canada. 3. REFERENCES Case, R. (1973): Use of true solar noon readings in quality control of NWS solar radiation network. Presented at 53rd Annual Meeting of AMS, St. Petersburg, Fla. , Feb. 1, 1973. Flowers, E., and P. Starke (1967): Results of a field trip to compare pyranometers. Unpub- lished manuscript. MacDonald, T. , and N. Foster (1954): Pyrheliome- ter calibration program of the U.S. Weather Bureau. Monthly Weather Review, 82(8) :219- 227. Nicolet, M. (1948): La Mesure du rayonnment so- laire. Inst. Roy. Met. Belg. Misc. fasc. 21. WMO (1971): CIMO guide to meteorological instru- ments and observing practices, Secretariat of WMO, Geneva. 33 1225 (Reprinted from Riii.lf.hn of thf. American Meteorological Society, Vol. 55, No. 4, April 1974, pp. 297-304] Printed in U. S. A. Radiation Sensor Comparisons During the GATE International Sea Trials (GIST) Kirby J. Hanson Sea-Air Interaction Laboratory, Atlantic Oceanographic and Meteorological Laboratories, NOAA, Miami, Fla. 33149 Abstract Radiation sensors on two ships of the U.S.S.R., one of Mexico, and one of the U.S. were compared during the GATE International Sea Trials (GIST), 2-10 August 1973. near20N, 60W. Pyranometer comparison showed that two instruments disagreed by 23%, but the remaining four pyranometers disagreed by less than 6%. The data also suggest the Yanishevsky and Eppley pyranometers have dissimilar cosine response characteristics which causes them to dis- agree by 4 mW cm"2 or less at low sun elevation angles. Pyrheliometers on the four ships were in agreement to within 1.7%. Two pyrgeometers (an Anstrdm type and Eppley type) differed by only 1.3%. An analysis of the GIST data suggests that, if condi- tions during the main field experiment are the same as in GIST, the three-day comparison period should be sufficient to reduce random errors in pyranometer mea- surements to 0.8%. This will allow determination of systematic pyranometer errors to well within the 5% level specified by ISMG. 1. Background The GARP Atlantic Tropical Experiment (GATE) is directed toward an improved understanding of the physi- cal processes in the tropical atmosphere and ocean which Bulletin American Meteorological Society play an important role in determining the main fea- tures of atmospheric circulation at all latitudes. The basis for achieving an improved understanding is the planned acquisition of a four-dimensional data set dur- ing the GATE, with highest density measurements in the tropical eastern Atlantic. Ships, aircraft, balloons, and satellites will be utilized as data collection platforms. Because many nations are participating with varied types of measuring instruments, it is vital that intercompari- sons between measuring systems be obtained in order to assure internal consistency of the data set. A pre-GATE intercomparison between four ships of three nations was planned by the International Scientific and Management Group (ISMG) for GATE and con- ducted 1-10 August 1973, at 20N, 60W. The intercom- parison was called the GATE International Sea Trials (GIST), and included the ships A. Korolov, U.S.S.R.; E. Krenkel, U.S.S.R.; Researcher, U.S.A.; and V. Uribe, Mexico. One of the primary purposes of the GIST was to test the adequacy of intercomparison methods planned for the GATE main field experiment. For example, such questions as how does ship spatial separation affect the comparison of sensors, and how much time is required to achieve an adequate comparison, had to be answered. Tests of measuring systems included surface meteorol- ogy, atmospheric sounding, atmospheric boundary layer, 297 1226 Vol. 55, No. I, April 1974 surface oceanography, and oceanographic sounding. In addition, radio communications, ship positioning, data exchange at sea, and international coordination were conducted during the GIST to study the feasibility of these operations during the three intercomparisons planned for the GATE main field experiment — which includes a larger number of ships. The International Coordinator of the GIST was Dr. Yuri Tarbeev (U.S.S.R.), Assistant Director of the 1SMG. Dr. Yerner Suomi (University of Wisconsin) was U.S. visiting scientist aboard the A. Korolov. The Chief Scien- tist of the Researcher was Dr. James Sparkman, NOAA. The Captain of the Researcher was Captain Lavon Posey, NOAA. The Radiation Subprogrammes were con- ducted on the ships by the following individuals: A. Korolov, Chief Meteorologist. V. V. Melnikov; E. Kren- kcl, Chief Meteorologist, T. F. Demechko, and special radiation consultant, E. I. Druzhinin; Researcher, the author and M. F. Poindexter; and V. Uribe, I. Galindo and A. Muhlia. The GIST agreements specified data exchange at sea. For the Radiation Subprogramme, pyranometer and pyrheliometer data were exchanged daily when small boat operation was possible. A small amount of data was exchanged by mail after the GIST. In this way a complete radiation data set was made available to each of the four participating ships and to the ISMG. The study reported here is based on the radiation data set available from the Researcher. At this writing there has been no formal data publication of the Radiation Subprogramme data. The author plans to publish the data set as a Technical Report of ERL/NOAA (Hanson, 1974). The period of GIST included three phases, as indi- cated in Table 1. Ship separation varied from 1-6 km during Phases I and III which were planned for inter- comparisons. However, during Phase II ships simulated the GATE data acquisition mode and separation be- tween ships was approximately 100 km. Although Phase I began on 1 August 1973, the beginning of the Radia- tion Subprogramme was delayed until 2 August 1973, because of the need for discussion, standardization of measurement schedules, and exchange of data forms. Table 1. GIST schedule — radiation subprogramme. Comments Phase I begins 0000 GMT Phase I ends 1800 GMT Phaxe II begins 0000 GMT Phase II ends 2359 GMT III Phase III begins 0600 GMT III III Phase III ends 1600 GMT In evaluation of the results of the GIST Radiation Subprogramme it is necessary to consider the nature ol differences between radiation measurements. In general. these differences can be attributd to three causes: 1) abso- lute calibration level and response characteristics ol the sensors; 2) sampling errors due to the spatial separation of the sensors; and 3) recording systems and data process- ing and integration methods. Prior to the experiment it was hoped that random measurement differences due to spatial separation of the instruments and certain data processing errors would be sufficiently small that useful information could be obtained concerning systematic differences due to absolute calibration level and response characteristics of the sensors. This proved to be the case, and the results are discussed in this report. In addition, information is presented on the amount of time required for such an experiment to minimize the random errors due to spatial separation of the sensors and data process- ing to the extent that systematic errors can be determined to sufficient accuracy to meet specifications for GATE. 2. Description and installation of sensors a. Pyranometers Pyranometers have a 180° field-of-view, and when used in a horizontal position facing upward, they mea- sure the total of the direct sun and diffuse sky compo- nents. They integrate solar radiation spectrally with approximate uniform sensitivity from 0.3 to 3 ^m. This includes about 99% of the solar radiation at the earth's surface. The upward facing pyranometer sensors on all four ships are described in Table 2 and the downward facing pyranometers are indicated in Table 3. Included in the test were six Yanishevsky pyranometers, four Eppley pyranometers, and one Moll Gorczynski type pyranom- eter. A unique feature of the comparison was the in- stallation on the Krenkel of a Yanishevsky M-80 and Eppley model 2 on identical gimbal platforms separated by approximately 1.5 m and identical potentiometric recording. This installation is shown in Fig. 1. The boom mounted pyranometers were installed 12 m forward of the bow on the Korolov and Krenkel and 10 m forward on the Researcher. Pyranometers were gimbal mounted on the Korolov and Krenkel but fixed relative to the ship in (average) horizontal position on the Researcher and Uribe. b. Pyrheliomelers Pyrheliometers measure the component of direct solar radiation incident on a surface normal to the sun's rays. Measurements are possible only under conditions in which clouds are not in the field of view of the instru- ment. The pyrheliometers of the four ships are indicated in Table 4. Measurements with these instruments were dis- continuous. The planned observation frequency was 30 min; however, this varied because of cloudiness at some observation times. The Yanishevsky pyrheliometers, on 298 1227 Bulletin American Meteorological Society Table 2. Upward facing pyranometers. 1. Ship name Korolov Krenkel Krenkel Krenkel Researcher I 'ribe I 'ribe 2. Sensor a. Position on ship Bow boom Bow Bow boom Bow Bow boom Bridge Bridge 1). Type and model Vanish. Yanish. Vanish. Epplev Epplev Eppley Moll-Gor. M-80 M-80 M-80 2 2 (bulb) c. Identification no. 43 2 5373 11539 12159 3192 683224 (1. Assumed sensitivity for data processing (mV cal-1 cm2 min1) 9.60 10.7 8.18 7.17 7.00 8.23 8.00 e. Temp, compensation No No No Yes Yes No No 3. Sampling rate (per hour) 30 45 50 45 Cont. Cont. Cont. 4. Integration method a. Electro/mechanical !). Visual X X X X X X X Table 3. Downward facing pyranometers. 1. Ship name Korolov Krenkel Researcher I 'ribe Sensor a. Position on ship Bow boom Bow boom Bow boom Boom b. Type and model Yanish. Yanish. Epplev Yanish. M-80 M-80 8-48 c. Identification no. 9 290 11990 1711 d. Assumed sensitivity for data processing (mV cal-' cm2 min1) 11.10 8.56 8.13 7.06 e. Temp, compensation No No Yes No 3. Sampling rate (per hour) 30 50 Cont. Cont. 4. Integration method a. Electro/mechanical b. Visual X X X X the Korolov and Krenkel, having a 10° field-of-view, were placed on a stationary platform to obtain measurements. The roll of those ships was sufficiently small that the sun remained in the pyrheliometer's field of view in spite of ship roll. On the Researcher, an adjustable tripod mount was used to manually direct the pyrheliometer (5° field-of-view) at the sun. On the Uribe, pyrheliometer (No. 54585) was gimbaled on 8 August. On previous days, stationary or handheld measurements were attempted. These attempts did not produce satisfactory data, and I hey are not reported here. c. Pyrgeometers Pyrgeometers were used to measure the IR radiation from sky and clouds incident on a horizontal surface. Only two pyrgeometers were present during the GIST; one on the Researcher and one on the Krenkel. These instruments were compared only once for a period of four hours and 15 min on the night of 5-6 August 1973 on the bow of the Krenkel. The sensors are described in. Table 5. "The instrument on the Krenkel was an Angstrom com- pensation pyrgeometer as developed by Angstrom (1905) and described by the Cotnite Special de I'Annee Geo- physique Internationale (1958). The instrument on the Researcher was an Eppley pyrgeometer which employs a KRS-5 hemisphere with interference filter on its inner surface (Eppley Lab, 1971). The composite transmission of the pyrgeometer hemispheric window is 4-50 /tm. 3. Pyranometer comparison Measurements with pyranometers were obtained dur- ing the period 2-10 August 1973. The resulting hourly and daily integrated radiation values for both upfacing and downfacing pyranometers were exchanged at sea Fie. 1. Installation on the bow of the E. Krenkel of an Eppley (Model 2) pyranometer and Yanishevsky (Model M-80) pyranometer on identical gimbal mounts. Mr. E. I. Druzhinin of the Main Geophysical Observatory, Leningrad, U.S.S.R., who was responsible for the installation is shown in the photo. 1228 299 Vol. 55, Ko. 1, April 1974 Table 4. Pyrheliometers. 1. Ship name Korolov Krenkel Researcher Uribe Uribe 2. Sensor a. Position on ship Mid-ship Mid-ship Bow Bridge Bridge b. Tvpe and model Yanish. Vanish. Epplev Yanish. Yanish. AT-50 AT-50 NIP c. Identification No. 6632 247 11946 797 54585 1. Assumed sensitivity for data processing (mV car1 cm"' min""1) 6.35 6.32 5.62 5.90 6.69 e. Temp, compensation No No Yes No No and serve as the lttsis for this report. The data will he published by Hanson (1974). a. Time averages In order to compare the pyranometers on days when the ships were in close location (Phases I and III), the data for 2, 3, 4, 5, 6, and 9 August have been averaged. August 10th was not used in the average because the Uribe was not present on that date. During this averag- ing period continuous measurements are available from all pyranometers except Nos. 3192 and 1711 on the Uribe. For this reason these two sensors are not included in the Phase I and III average. Hourly solar radiation averages were calculated for each sensor for the Phase I and III period. The results are given in Table 6. Plotted in Fig. 2 are hourly radia- tion values from four of the sensors which include the upper and lower range of measurements. From Fig. 2 it is clear that there exists systematic differences between sensors and these differences are consistent from hour to hour. The average daily radiation measurement from each upfacing pyranometer and for each day during the period 2-9 August 1973 is plotted as a time series in Fig. 3. Again, it is apparent that the significant differ- ences between the sensors are maintained from day to day. In Fig. 3 it can be seen that the sampling error due to spatial separation of the sensors is sufficiently small (even in Phase II) that the systematic differences between sensor measurements are not obscured. Finally, the data have been averaged for Phase I and III and for Phase I, II, and III to determine a single average daily radiation value for each instrument dur- ing both of these two time periods. The resulting aver- ages are shown in Fig. 4 as average irradiance values and in Table 7 as the ratio of the individual sensor response to the average of all sensors. Table 5. Pyrgeometers. 1. 2. Ship name Sensor Krenkel Researcher a. Type b. Identification No. Angstrom 6 Eppley 11540 c. .Assumed sensitivity for data processing (mV cal-1 cm2 min1) 2.22 4.965 From tli is information, it is clear that regardless of whether the data from only Phase I and III are used or whether all three Phases are included, the same rela- tive response of eacli sensor is obtained. The largest de- partures from the average of all sensors are by pyranom- eter No. 43 on the Korlov (+12.5%) and pyranometer No. 2 on the Krenkel (-10.7%); and the difference be- tween these two sensors is 23%. The other four pyranom- eters present in the intercomparison are within 2-4% of the average of all sensors. Subsequent to the field comparison, Galindo (Mexico) has advised that the radiation values for pyranometer No. 683224 should be increased by 5% due to a record- Hourly Solar Irradionca Aug 2,3.4.5.6.9 (19731 Hour Beginning (GMT) Fig. 2. Average hourly pyranometer values during Phases I and III. The data indicate the widest range of pyranometer responses. Data from other pyranometers not included here (for convenience of illustration) are given in Table 6. Doily Solar Irradionci Irradiancrj (MW/CM1) Fic. 3. Average daily pyranometer values, indicating the widest range of pyranometer responses. 300 1229 Bulletin American Meteorological Society Tarle 6. Phase (I and III) pyranometer data (m\V cm 2). Average for 2, 3, 4, 5, 6, and 9 August 1973. Ship AK EK AK EK EK RES RES VU VU EK Measurement H| HT H| H| H| H| HT HI H| H| Sensor tvpe Van. Van. Van. Van. Epp. Epp. Epp. MG Epp. Van. Sensor ident. 43 290 9 2 11539 12159 11990 683224 3192 5373 Sensor No. Hour beginning (GMT) • 2 3 4 5 6 7 8 9 10 9 2.72 0.00 0.70 0.87 1.40 0.48 0.10 1.70 0.20 10 14.28 2.83 2.22 10.62 10.03 11.00 1.68 12.42 12.10 11 35.57 3.80 3.54 29.30 31.05 34.15 2.88 31.80 31.43 12 58.67 3.85 4.10 49.22 52.43 51.47 2.55 54.60 52.43 13 80.87 3.62 4.25 67.43 71.90 75.73 2.55 70.23 72.70 14 94.78 3.92 4.25 77.92 87.45 90.97 2.65 83.27 89.15 15 105.70 4.12 4.47 80.50 89.68 97.42 2.62 90.67 Not 91.37 16 104.07 3.86 4.43 81.08 89.92 98.10 2.68 85.05 included 95.18 17 92.72 3.72 4.32 74.83 80.78 88.13 2.38 85.40 87.77 18 82.13 3.67 4.24 65.50 71.08 75.88 2.05 75.12 77.47 19 63.90 3.80 4.18 50.13 53.73 52.17 1.48 51.38 59.87 20 41.33 3.93 4.48 32.92 33.97 34.18 1.47 33.63 40.73 21 19.07 2.72 3.33 13.77 12.48 14.15 1.12 14.88 18.27 22 5.03 0.93 1.12 1.52 0.87 1.42 0.10 1.36 2.33 Dailv average 57.17 3.07 3.27 45.38 48.95 51.80 1.87 49.38 — 52.20 ing error which was detected after the experiment. This suggested correction has not been applied in the present report but should be considered applicable in any future use of this comparison. b. Sensor characteristics In evaluating the data, it was noted that the Yanishev- sky M-80 pyranometer appeared to give relatively higher values than the Eppley Model 2 at low sun elevation angles and the opposite for large sun elevation angles. To quantify this, the hourly data of three Yanishevsky pyranometers (Nos. 43, 2, and 5373) and two Eppley pyranometers (Nos. 11539 and 12159) were averaged for the period 2-9 August 1973. The results in Fig. 5 show the response of eacli of these two instrument types rela- tive to the average of all instruments, and in Fig. 6 the radiation differences are shown. From these two figures it appears that there are relatively high percentage differ- ences between these two instrument types at low sun elevation angles, although the energy differences at these angles is less than 4 mW cm"2. PHASE Iond m PHASE X.H.gndZX (Artroging Pcpioo August 2,3.4.5.6,9, 1973) (AUKjgiftgPtnod August 2-9, r973t 60 60 — .«»„(«., ».«)(«-«..] _...,.,.. 1 Y....M. „„iK.„.l 55 55 ■ =; «™~''..! "v."; » i8wk»; £?, *— E bIMtl 'or 1... NO .V5-IBO- bOO»l Irradianc* 50 (MW/CM*I . ^ [ "'.."',.■ " emu, ""Urn »° .'"' SO " — «,..i NO 68J2HH&..40.*') 45 :-«■—■ «•"— ■»"<-' 45 :-««■—< •«><«> 40 40 Fig. 4. Individual pyranometer averages for two different averaging periods. During Phases I and III the ships were separated by only a few kilometers, but during Phase II were separated by approximately 100 km. 4. Pyrheliometer comparison Measurements with pyrheliometers were obtained on each day during the period 2-10 August 1973. Not all ships obtained measurements each day, but a sufficient Table Measurement Sensor response relative to average of all sensors Ship Sensor N'o. Position sensor Type sensor Averaging period 2, 3, 4, 5. 6. and 9 August 1973 Averaging period 2-9 August 1973 A, Knrolov E. Krenkel Researcher V. Uribe E. Krenkel E. Krenkel 43 5373 12159 683224 11539 2 bow boom bow boom bow boom bridge bow bow Vanishev. Vanishev. Epplev M. G.' Eppley Vanishev. 1.125 1.027 1.019 0.972 0.963 0.893 1.120 1.021 1.024 0.981 0.961 0.891 1230 301 Vol 5?, \'o. L \fml 197-1 Relative Responce Vonishevshy Model M - 80 •\ Eppley Model 2 AH o (MW/fM'l Yomshevsky Mod ei M -80 4 -J "' \ \, X^y\^ h. • °~ - -o' 1 ;' \ Eppley Model 2 * i>-- ^ i- .. ' ' i ' ' Hour Beginning (GMT) Fie. 5. Relative response ol a group ol Vanishcvskv pvranomcters (Nos. 13. 2, and 5373) and a pail of l- .pplcv pyranomctcis (Nos. 115351 and 12159) during lIic period 2-9 August 1973, showing the variation in response due to sun elevation angle. number were obtained during the period to provide a useful comparison. Measurements were obtained once each 30 min when cloud conditions allowed. The pyrheli- ometer measurements were exchanged at sea and serve as the basis for this report. The basic data will be pub- lished by Hanson (1974). In order to compare sensors, data from pyrhcliometers on the Korolov, Researcher, and Uribe were compared individually with the pyrheliometer on the Krenkel (No. 247) by considering only those cases in which simultane- ous measurements were obtained. As indicated in Table 8, there were 76 simultaneous measurements between the Korolov and Krenkel, 63 between the Researcher and Krenkel, and 9 between the Uribe and Krenkel. Also given in Table 8 are the responses ol individual pyrheli- omcters, all relative to pyrheliometer No. 247 on the Krenkel. The results show that all lour pyrhcliometers are within 2% and that three of the four are within V ,,. The pyrheliometer on the Researcher has traceability to the International Pyrheliometric Scale, 1956, as do the pyrhcliometers on the Korolov and Krenkel; these three instruments differ at most by 1.7%. The pyrheliometer on the Uribe (No. 54585) was calibrated at sea against Yanishevsky control pyrheliometer No. 209 on board the Krenkel. This accounts for the close agreement (Table 8) between pyheliometers on the Krenkel and Uribe. Tai'.le 8. Comparison of pyrhcliometers. \u in her Sensor Sensor samples response Ship Tvpo sensor serial simul- relative Xo. taneous with Krenkel to Krenkel pyrheliometer .1 . Korolov Vanishev. 6632 76 0.993 E. Krenkel Vanishev. 247 — 1.000 Researcher Eppley 11946 63 0.983 V. Uribe Vanishev. 54585 9 1.002 Hour Beginning (GMT) Fir;. r>. OilForcnrc in radiation measured l>\ the pvranometei groups of Fig. 5. In comparing pvrheliomelcr measurements between two ships, it was found tli.it the average standard devia- tion ol the two measurements was from 1.5 to 2.0 m\V cm-. Since the error in sampling is probabl) random, the 1.5-2.0 mW cm-2 uncertainty associated with a single comparison will decrease (by 1/Vn) as the number ol samples is increased. 14ms, the uncertainty associated with the comparison of pyrhcliometers on the Korolov and Krenkel (in which 76 simultaneous measurements are available) is probably about 0.2 m\V cm"2 or near 0.4% of the measurement value. 5. Pyrgeometer comparison A comparison ol two pyrgeometers was carried out on the Krenkel from 0200-0615 GMT, 6 August 1973. The pyrgeometer types and their sensitivities are given in Table 5. A total of 35 simultaneous pyrgeometer measurements were obtained. The cloudiness varied from 1/10 to 4/10 cumulus during the comparison, and the temperature of the radiating surface of the Angstrom pyrgeometer varied from 26. 0-26. 9C. The measurements were exchanged at sea and will be published by Hanson (1974). The average atmospheric downward 1R radiation was 39.84 m\V cm"2 measured by the Krenkel pyrgeometer and 40.38 mW cm"" measured by the Researcher pyrgeom- eter; the averages differ 0.54 m\V cm"2 or 1.3%. 6. Implications about radiation sensor comparisons during the GATE main field experiment One of the primary purposes of GIST was to learn about the uncertainties involved in intercomparisons at sea and to determine the length of time required dur- ing comparisons in order to standardize the instruments to suitable accuracy. In this sense GIST was undertaken to learn how to conduct comparisons during the main field phases of the GATE. As indicated in the first section of this report, differ- ences between pyranomcters in comparisons at sea (in which instruments are separated by a few kilometers) 302 1231 lillllilill . I mi I n mi Mil. it) iih ll So, I, l\ 1. 111 be attributed to three sources. 1; ab>olute calibra- tion level and respon.se characteristics ol sensors; 2) sampling errors due to spatial separation <>1 sensors; and 3) recording systems and data integration methods. In the first case, the error in instrument response is mainly systematic but to a small extent could be random, if, for example, instrument characteristics differed and therefore instrument response would depend on cloudi- ness which is random, in the second case, the error in instrument response is mainly random because of the random nature of cloudiness and the physical separation of instruments by a lew kilometers. In the third case. the en or in measurement could be systematic from recording errors and also random due to visual integra- tion methods which are usually employed in data pro- cessing. With these error sources in mind, it is of interest to examine the GIST data in ordci to compute these errors and the time series needed to minimize random errors to a point where systematic differences between instru- ments can be resolved. 1 lie G1S I pyranometer data given in Section 3 ol this report show there were large systematic differences be- tween the measurement level ol some pyranometers. I he largest systematic difference between two pyranometers was 11.8 mW tin" or 23% of the daily integrated solar radiation. However, for the other lour pyranometers, differences between sensors were less than (>(,( and for some sensor pairs were less than L"1,,. 1 he ISMG has asked that pyranometers in GATE be standardized to within 5% (Kraus, 1973). As previously indicated, the random differences be- tween sensors is due to two sources: 1) spatial sampling, and 2) visual integration. We have evaluated the sum ol these two sources as a function ol the time period ovei which the data are integrated. 1 he curve shown in Fig. 7 represents sensor departure from the average of all sensors alter a systematic difference component has been removed. It is clear that for longer integrating time periods the sensor departure (Ironi the average ol all sensors) will decrease due io the random nature ol cloudiness and visual integration errors. INSTRUMENT DEPARTURE 2 (mw/cm1) MEASUREMENT DEPARTURE 4 ACCURACY REQUIREMENT - ISMG \ ' \ ■•■■ '■ r\V\.\ Fig. 7. Departure of pyranoiuetci seusoi clue to random errors in measurement. Time indicates tin* period <>\ci which the data arc integrated. lie 8. Departure of pyranomctei sen so l due to random errors of (1) spatial sampling and (2) data integration. Time indicates the period over which the data arc averaged. 15) using the data from the Krenkel on which three pyranometers were located, we have evaluated the crroi due to visual integration alone. In this way it was possi- ble to separate the total random erroi (fig- 7) into the two components as shown ill Fig. 8. and to examine how they varied as a function ol integration time. The information in Fig. 8 is useful in illustrating the relationship between the accuracy required for GATE measurements (5' <,) and the random errors ol spatial sampling and data integration; it also shows how this relationship depends on the period of integration. For example, if the length of the intercomparison were only one hour, it is evident from Fig. 8 that the de- parture ol a single pyranometer from the average of all pyranometers is likely to be near 6% due to the random error sources. This is larger than the accuracy require- ment specified by ISMG and, of course, would not pro- vide an adecpiate basis lor standardizing pyranometers. Clearly, it is most desirable to use a long integration period to minimize the random pan ol the measurement differences. The present ISMG plan suggests that three-day inter- comparisons will be conducted at sea during the main held phases with approximately the same ship spacing as in GIST. 1 he estimates in Fig. 8 suggest that if the pyranometer data arc integrated for a three-day period, the uncertainty in individual sensor measurement due to random sources will he about 0.8%, ol which about 2/3 is due to visual integration error and 1/3 is due to spatial sampling error. If two sensors are compared, the uncer- tainty due to random sources would double, amounting to nearly 1.6%. This means that in such comparisons sys- tematic differences between instruments can be removed with a residua] unccrtaint) ol 1.6%. Ibis is well within the 5% accuracy required b\ ISMG for pyranometer measurements in GATE. Whether these GIST results are realized in the GATE intercomparisons will depend on whether cloud condi- tions and integration methods in GIST are duplicated. Certainly, emphasis in p/e-GATE training should be placed on optimizing integration methods through the use of electrical, mechanical, ol compute! integration. In the U.S., prc-GATF planning and training is stressing the 1232 303 Vol. 55, S'o. /, Ipril I "7 / need for computer integration of the radiation nieasiue- ments in order to eliminate the visual integration error. Comparison of pyrlieliometers in GAIL intercom- parisons is not likely to present a problem because the instrument views only a 5-10° (ield-of-view, and measure- ments .ue not obtained when clouds are present between the sun and instrument. 1 bus, the spatial sampling eiroi lot p\ i heliometcr comparison will result only from hori- zontal inhomogeneities in atmospheric tiansmittaucc in areas between the clouds, and litis error is likely to be quite small. In addition, there is no need for time inte- gration with pyrheliomcter measurements. As discussed in Section 1. it is likel) that a single simultaneous mea- surement b\ two pvrheliomcters on separate ships will have an uncertainty of 1.5—2.0 m\V cm ~ or about 3-4'', nl the measurement value. However, this unccrlaintv will diii ease as the number ol measurements is increased. II. lot example, 1(3 simultaneous measurements ate ob- tained during the 3-day intercomparisons, the uncer- tainly will be reduced to l"(1 or less. In the U.S., pre- GA 1 L' training is specifying the need lot at least this number of measurements during each of the G.\ I L intercomparisons. References \ngstiom, K., 1905: I'clici die Anueiidiiiig tier clrkrischcn (Compensation -mclhode /in lieslimmung dei iiachlichcn Aiisstrahlting. Nova Acta Sue. Sci. I .sal.. Scr. I, I. Xo. 2. Comite Special de I'Annec Geophysique Internationale (CSAGI) Sub Commission foi Radiation Instructions of the Radiation Commission of IAM. 1958: Annah uj the Inter- national (.ieophysical Year, f'crgamon 1'iess, London, \"ol. 5. pp. 139-4 Hi. Epplcy Laboratory, Inc., 1971: Instrumentation for the mca- surement of components of solar and terrestrial radiation. (Unpublished document of the Epplcy Laboratory, Ncw- port, R.I . 31 pp.) Hanson. K., 197): Radiation Scnsoi Comparisons Dining the GATE International Sea liials (GIST). Submitted for pub bunion as a Technical Repoit of ERL/XOAA, Boulder, Colo. kiaus, II., 1973: flic Radiation Subprogrammc foi die GATE. GATE Report Xo. I. International Scientific & Management C.ioup for GATE, * >U pp., Appendixes. 304 1233 _^pMMOSP ^Ao^ U.S. DEPARTMENT OF COMMERCE Frederick B. Dent, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator ENVIRONMENTAL RESEARCH LABORATORIES Wilmot N. Hess, Director NOAA TECHNICAL REPORT ERL 301-AOML 14 Radiation Sensor Comparisons During the GATE International Sea Trials (GIST1 KIRBY J. HANSON BOULDER, COLO. APRIL 1974 For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402 1234 DISCLAIMER The NOAA Environmental Research Laboratories do not approve, recommend, or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to the NOAA Environmental Research Laboratories, or to this publication furnished by the NOAA Environ- mental Research Laboratories, in any advertising or sales promotion which would indicate or imply that the NOAA Environmental Research Laboratories approve, recommend, or endorse any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NOAA Environ- mental Research Laboratories publication. 1235 Preface This report, on the results of the comparison of radiation sensors at sea during the GATE International Sea Trials (GIST) , is based primarily on data which were exchanged at sea by small-boat operation. Similar data were received on the other three participating ships. A small amount of these data (about 1 day) was received from Mexico and the U.S.S.R. following the GIST. The article, given by reprint here, was published in the Bulletin of the American Meteorological Society to make the information available before the GATE. Because that journal usually does not publish the rather ex- tensive tabular data on which the article was based, we are combining the reprint article with the tables of data as appendices in this publication. 1236 CONTENTS Page Preface iii Reprint of Bulletin of the American Meteorological Society 1 Abstract 1 1 . Background 1 2. Description and installation of sensors 2 a. Pyranometers 2 b. Pyrheliometers 2 c. Pyrgeometers 3 3. Pyranometer comparison 3 a. Time averages 4 b. Sensor characteristics 5 4. Pyrheliometer comparison 5 5 . Pyrgeometer comparison 6 6. Implications about radiation sensor comparisons during the GATE main field experiment 6 References 8 Appendix A. Pyranometer data 9 Appendix B. Pyrheliometer data 19 Appendix C. Pyrgeometer data 29 1237 Radiation Sensor Comparisons During the GATE International Sea Trials (GIST)* Kii by J. Hanson Sea-Air Interaction Laboratory, Atlantic Oceanographic and Meteorological Laboratories, NOAA, Miami, Fla. 33119 Abstract Radiation sensors on two ships of the U.S.S.R., one of Mexico, and one of the U.S. were compared during the GATE International Sea Trials (GIST), 2-10 August 1973, near20N, 60W. Pyranometer comparison showed that two instruments disagreed by 23%, but the remaining four pyranometers disagreed by less than 6%. The data also suggest the Yanishevsky and Eppley pyranometers have dissimilar cosine response characteristics which causes them to dis- agree by 4 mW cm"2 or less at low sun elevation angles. Pyrheliometers on the four ships were in agreement to within 1.7%. Two pyrgeometers (an Anstrom type and Eppley type) differed by only 1.3%. An analysis of the GIST data suggests that, if condi- tions during the main field experiment are the same as in GIST, the three-day comparison period should be sufficient to reduce random errors in pyranometer mea- surements to 0.8%. This will allow determination of systematic pyranometer errors to well within the 5% level specified by ISMG. 1. Background The GARP Atlantic Tropical Experiment (GATE) is directed toward an improved understanding of the physi- cal processes in the tropical atmosphere and ocean which play an important role in determining the main fea- tures of atmospheric circulation at all latitudes. The basis for achieving an improved understanding is the planned acquisition of a four-dimensional data set dur- ing the GATE, with highest density measurements in the tropical eastern Atlantic. Ships, aircraft, balloons, and satellites will be utilized as data collection platforms. Because many nations are participating with varied types of measuring instruments, it is vital that intercompari- sons between measuring systems be obtained in order to assure internal consistency of the data set. A pre-GATE intercomparison between four ships of three nations was planned by the International Scientific and Management Group (ISMG) for GATE and con- ducted 1-10 August 1973, at 20N, 60W. The intercom- parison was called the GATE International Sea Trials (GIST), and included the ships A. Korolov, U.S.S.R.; E. Krenkel, U.S.S.R.; Researcher, U.S.A.; and V. Uribe, Mexico. One of the primary purposes ot the GIST was to test the adequacy of intercomparison methods planned for the GATE main field experiment. For example, such questions as how does ship spatial separation affect the comparison of sensors, and how much time is required to achieve an adequate comparison, had to be answered. Tests of measuring systems included surface meteorol- ogy, atmospheric sounding, atmospheric boundary layer, •[Reprinted from Bulletin of the American Mitioroi.oi.kal Society, Vol. 55, No. 4, April 1971, pp. 297-304] Printed in U. S. A. 1238 surface oceanography, and oceanographic sounding. In addition, radio communications, ship positioning, data exchange at sea, and international coordination were conducted during the GIST to study the feasibility ol these operations during the three intercomparisons planned for the GATE main field experiment — which includes a larger number of ships. The International Coordinator of the GIST was Dr. Yuri Tarbccv (U.S.S.R.), .Assistant Director of the ISMG. Dr. Verner Suomi (University of Wisconsin) was U.S. visiting scientist aboard the A. Korolov. The Chief Scien- tist of the Researcher was Dr. James Sparkman, NOAA. The Captain of the Researcher was Captain Lavon Posey, NOAA. The Radiation Subprogrammes were con- ducted on the ships by the following individuals: A. Korolov, Chief Meteorologist, V. V. Melnikov; E. Kren- kel, Chief Meteorologist, T. F. Demechko, and special radiation consultant, E. I. Druzhinin; Researcher, the author and M. F. Poindexter; and V. Uribc, I. Galindo and A. Muhlia. The GIST agreements specified data exchange at sea. For the Radiation Subprogramme, pyranometer and pyrheliometcr data were exchanged daily when small boat operation was possible. A small amount of data was exchanged by mail after the GIST. In this way a complete radiation data set was made available to each of the four participating ships and to the ISMG. The study reported here is based on the radiation data set available from the Researcher. At this writing there has been no formal data publication of the Radiation Subprogramme data. The author plans to publish the data set as a Technical Report of ERL/NOAA (Hanson, 1974). The period of GIST included three phases, as indi- cated in Table 1. Ship separation varied from 1-6 km during Phases I and III which were planned for inter- comparisons. However, during Phase II ships simulated the GATE data acquisition mode and separation be- tween ships was approximately 100 km. Although Phase I began on 1 August 1973. the beginning of the Radia- tion Subprogramme was delayed until 2 August 1973, because of the need for discussion, standardization of measurement schedules, and exchange of data forms. Table 1. GIST schedule — radiation subprogramme. Julian day Date GIST phase Comments 214 215 216 217 218 2 August 1973 3 4 5 6 7 8 9 10 11 I I I I I Phase I begins 0000 GMT Phase I ends 1800 GMT 219 220 II II Phaxe II begins 0000 GMT Phase II ends 2359 GMT 221 222 223 III III III Phase III begins 0600 GMT Phase III ends 1600 GMT In evaluation of the results of the GIST Radiation Subprogramme it is necessary to consider the nature of differences between radiation measurements. In general, these differences can be attributd to three causes: 1) abso- lute calibration level and response characteristics of the sensors; 2) sampling errors due to the spatial separation of the sensors; and 3) recording systems and data process- ing and integration methods. Prior to the experiment it was hoped that random measurement differences due to spatial separation of the instruments and certain data processing errors would be sufficiently small that uselul information could be obtained concerning systematic differences due to absolute calibration level and response characteristics of the sensors. This proved to be the case, and the results are discussed in this report. In addition, information is presented on the amount of time required for such an experiment to minimize the random errors due to spatial separation of the sensors and data process- ing to the extent that systematic errors can be determined to sufficient accuracy to meet specifications for GATE. 2. Description and installation of sensors a. Pyranometers Pyranometers have a 180° field-of-view, and when used in a horizontal position facing upward, they mea- sure the total of the direct sun and diffuse sky compo- nents. They integrate solar radiation spectrally with approximate uniform sensitivity from 0.3 to 3 /u.m. This includes about 99% of the solar radiation at the earth's surface. The upward facing pyranometer sensors on all four ships are described in Table 2 and the downward facing pyranometers are indicated in Table 3. Included in the test were six Yanishevsky pyranometers, four Eppley pyranometers, and one Moll Gorczynski type pyranom- eter. A unique feature of the comparison was the in- stallation on the Krenkel of a Yanishevsky M-80 and Eppley model 2 on identical gimbal platforms separated by approximately 1.5 m and identical potentiometric recording. This installation is shown in Fig. I. The boom mounted pyranometers were installed 12 in forward of the bow on the Korolov and Krenkel and 10 m forward on the Researcher. Pyranometers were gimbal mounted on the Korolov and Krenkel but fixed relative to the ship in (average) horizontal position on the Researcher and Uribe. b. Pyrheliometers Pyrheliometers measure the component of direct solai radiation incident on a surface normal to the sun's rays. Measurements are possible only under conditions in which clouds are not in the field of view of the instru- ment. The pyrheliometers of the four ships are indicated in Table 4. Measurements with these instruments were dis- continuous. The planned observation frequency was 30 min; however, this varied because of cloudiness at some observation times. The Yanishevsky pyrheliometers, on 1239 Table 2 Upward fac ng pyranometers. 1. Ship name Korolov Krenkel Krenkel Krenkel Researcher Uribe Uribe 2. Sensor a. Position on ship Bow boom Bow Bow boom Bow Bow boom Bridge Bridge b. Type and model Yanish. Yanish. Yanish. Eppley Eppley Eppley Moll-Gor. M-80 M-80 M-80 2 2 (bulb) c. Identification no. 43 2 5373 11539 12159 3192 683224 d. Assumed sensitivity for data processing (mV cal-1 cm2 min1) 9.60 10.7 8.18 7.17 7.00 8.23 8.00 e. Temp, compensation No No No Yes Yes No No 3. Sampling rate (per hour) 30 45 50 45 Cont. Cont. Cont. 4. Integration method a. Electro/mechanical b. Visual X X X X X X X Tahle 3. Downward facing pyranometers. 1. Ship name Korolov Krenkel Researcher Uribe Sensor a Position on ship Bow boom Bow boom Bow boom Boom 1). Type and model Yanish. Yanish. Epplev Vanish. M-80 M-80 8-48 c. Identification no. 9 290 11990 1711 d. Assumed sensitivity for data processing (mV cal-1 cm2 min1) 11.10 8.56 8.13 7.06 e. Temp, compensation No No Yes No- 3. Sampling rate (per hour) 30 50 Cont. Cont. 4. Integration method a. Electro/mechanical b. Visual X X X X the Korolov and Krenkel, having a 10° field-of-view, were placed on a stationary platform to obtain measurements. The roll of those ships was sufficiently small that the sun remained in the pyrheliometer's field of view in spite of ship roll. On the Researcher, an adjustable tripod mount was used to manually direct the pyrheliometer (5° field-of-view) at the sun. On the Uribe, pyrheliometer (No. 54585) was gimbaled on 8 August. On previous days, stationary or hand-held measurements were attempted. These attempts did not produce satisfactory data, and they are not reported here. c. Pyr geometers Pyrgeometers were used to measure the IR radiation from sky and clouds incident on a horizontal surface. Only two pyrgeometers were present during the GIST; one on the Researcher and one on the Krenkel. These instruments were compared only once for a period of four hours and 15 min on the night of 5-6 August 1973 on the bow of the Krenkel. The sensors are described in Table 5. The instrument on the Krenkel was an Angstrom com- pensation pyrgeometer as developed by Angstrom (1905) and described by the Comite Special de I'Annee Geo- physique Internationale (1958). The instrument on the Researcher was an Eppley pyrgeometer which employs a KRS-5 hemisphere with interference filter on its inner surface (Eppley Lab, 1971). The composite transmission of the pyrgeometer hemispheric window is 4-50 jum. 3. Pyranometer comparison Measurements with pyranometers were obtained dur- ing the period 2-10 August 1973. The resulting hourly and daily integrated radiation values for both upfacing and downfacing pyranometers were exchanged at sea Fig. 1. Installation on the bow of the E. Krenkel of an Eppley (Model 2) pyranometer and Yanishevsky (Model M-80) pyranometer on identical gimbal mounts. Mr. E. I. Druzhinin of the Main Geophysical Observatory, Leningrad, U.S.S.R., who was responsible for the installation is shown in the photo. 1240 Table 4. Pyrheliometers. 1. Ship name Korolov Krenkel Researcher Uribe Uribe 2. Sensor a. Position on ship Mid-ship Mid-ship Bow Bridge Bridge b. Type and model Vanish. Yanish. Eppley Yanish. Yanish. AT-50 AT-50 NIP c. Identification No. 6632 247 11946 797 54585 d. Assumed sensitivity for data processing (mV cal^1 cm-2 min1) 6.35 6.32 5.62 5.90 6.69 e. Temp, compensation No No Yes No No and serve as the basis for this report. The data will be published by Hanson (1974). a. Time averages In order to compare the pyranometers on days when the ships were in close location (Phases I and III), the data for 2, 3, 4, 5, 6, and 9 August have been averaged. August 10th was not used in the average because the Uribe was not present on that date. During this averag- ing period continuous measurements are available from all pyranometers except Nos. 3192 and 1711 on the Uribe. For this reason these two sensors are not included in the Phase I and III average. Hourly solar radiation averages were calculated for each sensor for the Phase I and III period. The results are given in Table 6. Plotted in Fig. 2 are hourly radia- tion values from four of the sensors which include the upper and lower range of measurements. From Fig. 2 it is clear that there exists systematic differences between sensors and these differences are consistent from hour to hour. The average daily radiation measurement from each upfacing pyranometer and for each day during the period 2-9 August 1973 is plotted as a time series in Fig. 3. Again, it is apparent that the significant differ- ences between the sensors are maintained from day to day. In Fig. 3 it can be seen that the sampling error due to spatial separation of the sensors is sufficiently small (even in Phase II) that the systematic differences between sensor measurements are not obscured. Finally, the data have been averaged for Phase I and III and for Phase I, II, and III to determine a single average daily radiation value for each instrument dur- ing both of these two time periods. The resulting aver- ages are shown in Fig. 4 as average irradiance values and in Table 7 as the ratio of the individual sensor response to the average of all sensors. Table 5. Pyrgeometers. 1. 2. Ship name Sensor Krenkel Researclier a. Type b. Identification No. Angstrom 6 Eppley 11540 c. Assumed sensitivity for data processing (mV cal-1 cm2 min1) 2.22 4.965 From this information, it is clear that regardless of whether the data from only Phase I and III are used or whether all three Phases are included, the same rela- tive response of each sensor is obtained. The largest de- partures from the average of all sensors are by pyranom- eter No. 43 on the Korlov (+12.5%) and pyranometer No. 2 on the Krenkel (—10.7%); and the difference be- tween these two sensors is 23%. The other four pyranom- eters present in the intercomparison are within 2-4% of the average of all sensors. Subsequent to the field comparison, Galindo (Mexico) has advised that the radiation values for pyranometer No. 683224 should be increased by 5% due to a record- Hourly Solar Irradiance Aug 2.5.4,5.6.9 [1973] Hour Beginning (GMT) Fic. 2. Average hourly pyranometer values during Phases I and III. The data indicate the widest range of pyranometer responses. Data from other pyranometers not included here (for convenience of illustration) are given in Table 6. Fic. 3. Average daily pyranometer values, indicating the widest range of pyranometer responses. 1241 Table 6. Phase (I and III) pyranometer data (mW cm 2). Average for 2, 3, 4, 5, 6, and 9 August 1973. Ship AK EK AK EK EK RES RES VU VU EK Measurement H| HT HT HI HI HI HT H| m HI Sensor type Yan. Yan. Yan. Yan. Epp. Epp. Epp. MG Epp. Yan. Sensor ident. 43 290 9 2 11539 12159 11990 683224 3192 5373 Sensor No. Hour beginning (GMT) l 2 3 4 5 6 7 8 9 10 9 2.72 0.00 0.70 0.87 1.40 0.48 0.10 1.70 0.20 10 14.28 2.83 2.22 10.62 10.03 11.00 1.68 12.42 12.10 11 35.57 3.80 3.54 29.30 31.05 34.15 2.88 31.80 31.43 12 58.67 3.85 4.10 49.22 52.43 51.47 2.55 54.60 52.43 13 80.87 3.62 4.25 67.43 71.90 75.73 2.55 70.23 72.70 14 94.78 3.92 4.25 77.92 87.45 90.97 2.65 83.27 89.15 15 105.70 4.12 4.47 80.50 89.68 97.42 2.62 90.67 Not 91.37 16 104.07 3.86 4.43 81.08 89.92 98.10 2.68 85.05 included 95.18 17 92.72 3.72 4.32 74.83 80.78 88.13 2.38 85.40 87.77 18 82.13 3.67 4.24 65.50 71.08 75.88 2.05 75.12 77.47 19 63.90 3.80 4.18 50.13 53.73 52.17 1.48 51.38 59.87 20 41.33 3.93 4.48 32.92 33.97 34.18 1.47 33.63 40.73 21 19.07 2.72 3.33 13.77 12.48 14.15 1.12 14.88 18.27 22 5.03 0.93 1.12 1.52 0.87 1.42 0.10 1.36 2.33 Daily ^ verage 57.17 3.07 3.27 45.38 48.95 51.80 1.87 49.38 — 52.20 ing error which was detected after the experiment. This suggested correction has not been applied in the present report but should be considered applicable in any future use of this comparison. b. Sensor characteristics In evaluating the data, it was noted that the Yanishev- sky M-80 pyranometer appeared to give relatively higher values than the Eppley Model 2 at low sun elevation angles and the opposite for large sun elevation angles. To quantify this, the hourly data of three Yanishevsky pyranometers (Nos. 43, 2, and 5373) and two Eppley pyranometers (Nos. 11539 and 12159) were averaged for the period 2-9 August 1973. The results in Fig. 5 show the response of each of these two instrument types rela- tive to the average of all instruments, and in Fig. 6 the radiation differences are shown. From these two figures it appears that there are relatively high percentage differ- ences between these two instrument types at low sun elevation angles, although the energy differences at these angles is less than 4 mW cm-2. PHASE land EI (Averaging Period August 2.3,4.5.6.9.1973) PHASE I.I.MII (Averaging Period August 2-9. 1973) Solor Irradiance (MWVCM1) Fig. 4. Individual pyranometer averages for two different averaging periods. During Phases I and III the ships were separated by only a few kilometers, but during Phase II were separated by approximately 100 km. 4. Pyrheliomerer comparison Measurements with pyrheliometcrs were obtained on each day during the period 2-10 August 1973. Not all ships obtained measurements each day, but a sufficient Table 7. Measurement Sensor response relative to average of all sensors Ship Sensor No. Position sensor Type sensor Averaging period 2, 3, 4, 5, 6, and 9 August 1973 Averaging period 2-9 August 1973 A. Korolov 43 bow boom Yanishev. 1.125 1.120 E. Krenkel 5373 bow boom Yanishev. 1.027 1.021 Researcher 12159 bow boom Eppley 1.019 1.024 V. Uribe 683224 bridge M. G. 0.972 0.981 E. Krenkel 11539 bow Eppley 0.963 0.961 E. Krenkel 2 bow Yanishev. 0.893 0.891 1242 Relative Responce I 05 Yamshexsky Model M-80 / :\ Eppley Model 2 AH (MW/CM2) Yanishevsky Model M-80 Eppley Model 2 Hour Beginning (GMT) Fic. 5. Relative response of a group of Yanishcvsky pyranometers (Nos. 43, 2, and 5373) and a pair of Eppley pyranometers (Nos. 11539 and 12159) during the period 2-9 August 1973, showing the variation in lcsponse due to sun elevation angle. number were obtained during the period to provide a useful comparison. Measurements were obtained once each 30 min when cloud conditions allowed. The pyrheli- ometer measurements were exchanged at sea and serve as the basis for this report. The basic data will be pub- lished by Hanson (1974). In order to compare sensors, data from pyrheliometers on the Korolov, Researcher, and Uribe were compared individually with the pyrheliometer on the Krenkel (No. 247) by considering only those cases in which simultane- ous measurements were obtained. As indicated in Table 8, there were 76 simultaneous measurements between the Korolov and Krenkel, 63 between the Researcher and Krenkel, and 9 between the Uribe and Krenkel. Also given in Table 8 are the responses of individual pyrheli- ometers, all relative to pyrheliometer No. 247 on the Krenkel. The results show that all four pyrheliometers are within 2% and that three of the four are within 1%. The pyrheliometer on the Researcher has traceability to the International Pyrheliometric Scale, 1956, as do the pyrheliometers on the Korolov and Kienkel; these three instruments differ at most by 1.7%. The pyrheliometer on the Uribe (No. 54585) was calibrated at sea against Yanishevsky control pyrheliometer No. 209 on board the Krenkel. This accounts for the close agreement (Table 8) between pyheliometers on the Krenkel and Uribe. Table 8. Comparison of pyrheliometers. Number Sensor Ship Type sensor Sensor serial No. samples simul- taneous with Krenkel response relative to Krenkel pyrheliometer A . Korolov Yanishev. 6632 76 0.993 E. Krenkel Yanishev. 247 — 1.000 Researcher Eppley 11946 63 0.983 V. Uribe Yanishev. 54585 9 1.002 Hour Beginning (GMT) Fie. 6. Difference in radiation measured by the pyranomctcr groups of Fig. 5. In comparing pyrheliometer measurements between two ships, it was found that the average standard devia- tion of the two measurements was from 1,5 to 2.0 m\V cm"3. Since the error in sampling is probably random. the 1.5-2.0 mW cm-2 uncertainty associated with a single comparison will decrease (by 1/Vn) as the number ol samples is increased. Thus, the uncertainty associated with the comparison of pyrheliometers on the Koroloxi and Krenkel (in which 76 simultaneous measurements are available) is probably about 0.2 mVV cm"2 or near 0.4% of the measurement value. 5. Pyrgeometer comparison A comparison of two pyrgeometers was carried out on the Krenkel from 0200-0615 GMT, 6 August 1973. The pyrgeometer types and their sensitivities are given in Table 5. A total of 35 simultaneous pyrgeometer measurements were obtained. The cloudiness varied from 1/10 to 4/10 cumulus during the comparison, and the temperature of the radiating surface of the Angstrom pyrgeometer varied from 26. 0-26. 9C. The measurements were exchanged at sea and will be published by Hanson (1974). The average atmospheric downward IR radiation was 39.84 mW cm"5 measured by the Krenkel pyrgeometer and 40.38 mW cm"2 measured by the Researcher pyrgeom- eter; the averages differ 0.54 mW cm"2 or 1.3%. 6. Implications about radiation sensor comparisons during the GATE main field experiment One of the primary purposes of GIST was to learn about the uncertainties involved in intercomparisons at sea and to determine the length of time required dur- ing comparisons in order to standardize the instruments to suitable accuracy. In this sense GIST was undertaken to learn how to conduct comparisons during the main field phases of the GATE. As indicated in the first section of this report, differ- ences between pyranometers in comparisons at sea (in which instruments are separated by a few kilometers) 1243 can be attributed to three sources: 1) absolute calibra- tion level and response characteristics of sensors; 2) sampling errors due to spatial separation of sensors; and 3) recording systems and data integration methods. In the first case, the error in instrument response is mainly systematic but to a small extent could be random, if, for example, instrument characteristics differed and therefore instrument response would depend on cloudi- ness which is random. In the second case, the error in instrument response is mainly random because of the random nature of cloudiness and the physical separation of instruments by a few kilometers. In the third case, the error in measurement could be systematic from recording errors and also random due to visual integra- tion methods which are usually employed in data pro- cessing. With these error sources in mind, it is of interest to examine the GIST data in order to compute these errors and the time series needed to minimize random errors to a point where systematic differences between instru- ments can be resolved. The GIST pyranometer data given in Section 3 of this report show there were large systematic differences be- tween the measurement level of some pyranometers. The largest systematic difference between two pyranometers was 11.8 mW cm"2 or 23% of the daily integrated solar radiation. However, for the other four pyranometers, differences between sensors were less than 6% and for some sensor pairs were less than 2%. The ISMG has asked that pyranometers in GATE be standardized to within 5% (Kraus, 1973). As previously indicated, the random differences be- tween sensors is due to two sources: 1) spatial sampling, and 2) visual integration. We have evaluated the sum of these two sources as a function of the time period over which the data are integrated. The curve shown in Fig. 7 represents sensor departure from the average of all sensors after a systematic difference component has been removed. It is clear that for longer integrating time periods the sensor departure (from the average of all sensors) will decrease due to the random nature of cloudiness and visual integration errors. INSTRUMENT DEPARTURE 2 (mw/cm1) MEASUREMENT DEPARTURE 4 (%) >V. ACCURACY REQUIREMENT - ISMG _// ' / //^^ .Total Rondom Error - / / \V \ \ \ A \ \ \ \\ A \ \ A LTw^b — 2 3 DAYS Fig. 7. Departure of pyranometer sensor clue to random errors in measurement. Time indicates the period over which the data arc integrated. Fig. 8. Departure of pyranometer sensor due to random errors of (1) spatial sampling and (2) data integration. Time indicates the period over which the data are averaged. By using the data from the Krenkel on which three pyranometers were located, we have evaluated the error due to visual integration alone. In this way it was possi- ble to separate the total random error (Fig. 7) into the two components as shown in Fig. 8, and to examine how they varied as a function of integration time. The information in Fig. 8 is useful in illustrating the relationship between the accuracy required for GATE measurements (5%) and the random errors of spatial sampling and data integration; it also shows how this relationship depends on the period of integration. For example, if the length of the intercomparison were only one hour, it is evident trom Fig. 8 that the de- parture of a single pyranometer from the average of all pyranometers is likely to be near 6% clue to the random error sources. This is larger than the accuracy require- ment specified by ISMG and, of course, would not pro- vide an adequate basis for standardizing pyranometers. Clearly, it is most desirable to use a long integration period to minimize the random part of the measurement differences. The present ISMG plan suggests that three-day inter- comparisons will be conducted at sea during the main field phases with approximately the same ship spacing as in GIST. The estimates in Fig. 8 suggest that if the pyranometer data are integrated for a three-day period, the uncertainty in individual sensor measurement due to random sources will be about 0.8%, of which about 2/3 is due to visual integration error and 1/3 is due to spatial sampling error. If two sensors are compared, the uncer- tainty due to random sources would double, amounting to nearly 1.6%. This means that in such comparisons sys- tematic differences between instruments can be removed with a residual uncertainty of 1.6%. This is well within the 5% accuracy required by ISMG lor pyranometer measurements in GAIT. Whether these GIST results are realized in the GATE intercomparisons will depend on whether cloud condi- tions and integration methods in GIST are duplicated. Certainly, emphasis in pre-GATE training should be placed on optimizing integration methods through the use of electrical, mechanical, or computer integration. In the U.S., pre-GATE planning and training is stressing the 1244 need for computer integration of the radiation measure- ments in order to eliminate the visual integration error. Comparison of pyrheliometers in GATE intercom- parisons is not likely to present a problem because the instrument views only a 5-10° field-of-view, and measure- ments are not obtained when clouds are present between the sun and instrument. Thus, the spatial sampling error for pyrheliometer comparison will result only from hori- zontal inhomogeneities in atmospheric transmittance in areas between the clouds, and this error is likely to be quite small. In addition, there is no need for time inte- gration with pyrheliometer measurements. As discussed in Section 4, it is likely that a single simultaneous mea- surement by two pyrheliometers on separate ships will have an uncertainty of 1.5-2.0 raW cm- or about 3-4% of the measurement value. However, this uncertainty will decrease as the number of measurements is increased. If, for example, 16 simultaneous measurements are ob- tained during the 3-day intercomparisons, the uncer- tainty will be reduced to 1% or less. In the U.S., pre- GATE training is specifying the need for at least tltis number of measurements during each of the GATE intercomparisons. References Angstrom, K., 1905: Uebcr die An wenching der clckrischen Kompensation-mcthode zur Bestimmung der nachlichen Ausstrahlung. Nova Acta Soc. Sci. Usal., Ser. 4, 1, No. 2. Comite Special de l'Annee Geophysique Internationale (CSAGI) Sub Commission for Radiation Instructions of the Radiation Commission of IAM, 1958: Annals of the Inter- national Geophysical Year, Pergamon Press, London, Vol. 5, pp. 439-440. Eppley Laboratory, Inc., 1971: Instrumentation for the mea- surement of components of solar and terrestrial radiation. (Unpublished document of the Eppley Laboratory, New- port, R.I , 31 pp.) Hanson, K., 1974: Radiation Sensor Comparisons During the GATE International Sea Trials (GIST). Submitted for pub- lication as a Technical Report of ERL/NOAA, Boulder, Colo. Kraus, H., 1973: The Radiation Subpiogrammc for the GATE. GATE Report No. 4, International Scientific & Management Gioup for GATE, d'J, pp., Appendixes. 1245 Appendix A. 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C CN P -> P -H > ~ UJ CO v3- CM CNl CO P -> O CO t> EC ^ sC O • ON co p. on o; x k rH on • m CO CJjrH W -> ChCM KX WH ON • co ^ -* 2h w re wjtH c « •* CO W EC >H CM irf <- re . c c :*s «- re ov UX>-c - on CO CO CM 00 00 r~ CO CM m C CM u~l CM CM r^ r- O NC 00 oooNr~oomcocN r-~00CCincMiH>3'u-lCOCN|rHsCCMr^ OmNMflNOOCONCOH CNi-jmrNOONOc^roMH or^oocomvoocoommcocsico CO-3-CO»a--3--3-u-i-3->3->3-rH OfOrHONCOONrHOOi— ICJNCOONOm CMCOCSCOCNICOCOCOCNICMCNCM u 3 o . EC Xi 60 a •H C C r-N "Sofe 0> e> ocmcMcooNCMmcMOr^cor^ONCO HrNCOHrNSt^HvOHCOH-JN mv£>moor^ooooovo-*iH CO ~3- c CM CO -3 ^5 CM m ON O rH Nfn-jmiOMio^OHM rHrHi— IHHHHHCNNM cu IB rd u 0) r*S > 1-1 r3 D O >^JZ •H s» cfl rH a ^-^ 1253 m a 3 < < < PS w H b 1 ^ 5 EL O. W o-'in an «- s 3^ c o co cj\ >-" CN c CO B 01 Lj 3 CO ca 0) . O r C cn O CO c 0) C/3 CN m io r^ cn ■— ir~oocNiu~>vor-"-c\ii/"ii— ' O-JIAOJWHIXJMHrtHOi-l ON-srom^fsivo-a-cciocNi-i CNiO\or^oor-~r»»r^Locoi-i OOONHvOCCMMNHOOOmO ■HCNCNCNCNCNCNCNr-ICNi-l stntHinrMcNmm^a-i-H-^-rovoo 00\£H0nff\rlrlOlfl\0(«)rlH cN-4HvOaiHCCkOOOvn>ffi N-JNCOHNHOOON 3 MS O » o H r-l CO » «* vO tH LO o LA r-i Csl co m -J" co CO co CO co CO CN en n On 00 co LO' o\ r~- -» SO i-H J vD CO CO m 00 lO O i— 1 O 1— 1 r^ 00 vD CO i-H LO CTtO'-tCNCOO-mvOr^OOONOr-iCsl •Hi-HiHtHiHi— I H H H H (N IN IN a) 60 ca m cu > *-> rd 3 o >. JS H •H a, D, rsi w W EC cum w ^ c c c o O LO 1^ co vO © CO 00 O tn i-H (" i -J r^ 00 o> o r-~ Jffl\OvO .-H -3- oovoH<-o\ovo>cccj\3.>3-fs, co c-> Oi-tcNLorsio\cMcMtnmu-iinr»-o O O m uOvOr-(00(NOvOOOr-lvOiHLriCNO CO nvDOi-toOiot^cMo-ir^\ooou-i riniooo^oovoinvonH 53.65 CTi Ot-lcs4ro>3-u-i^Of--00HiHiHi-(i-liHrHiHiHt-lcNCN u fl 3 O •H .* Cd rH Q ■-' 1255 Appendix B. Pyrheliometer data 1256 CO ON CM ■U to 3 00 3 a W H coooooooooooooooocooo -3 ch-cvocovcoh-ocfoco lo r- «-i =t o o o I IT • u ^ r- c\ x r» cc x. cc «- r^ cm o .d- N. CC ITvCvCvC vC >X vT v.C IT LT LT> d" »- • •• »-( ^ C d I*- O C O K. rH rH U~ C U" K. h- vf P~ it u. ^^^fv[^^^^^ r^ vf ir it it j r tv ■z Ll t- •-^ HXio^aooMoooU1 i-o o .n o r- co .o -c in in vDvOv^r-r^h-f^r^h-vD ^ vo in j ki cv h CL, tr r. r. ic k to ic r to o io ic r k;- r. id K"; mo k" c: k; Lu >- 2 £ cc ec cc cc cc cc cc or cc cc cc cc cc or or cc cr cc oc Co cv <\ c\i r\ • cm oj Cvj cv c\.i c\, cm oo cm c\' cvi c\ cv c\ cm cv Ct ooooooocoooooooooooco 3 r03r00rOOr03."OJ3"OOrOO'Oor03r03rO X »H_^_r_l_(,H_(_,_.rH,-|.H_<_^H_OvjrMCMC\J 1257 CO CT\ CO 3 ooooooooooooocoocoooooo 3 > 1/1 a LU \ cr ococciooircocrOiiCHri^cvCGciTiocvC IT, CM rr in IT d- cc cc co cc cc LC Cf CV cc cc cc «H IT, cr r- ro r- vo vC LO CM Ir. < < a OS w H UJ 6 H -1 W EC Bj >H a. > LT Ll t>ococo^d- i-- a. a oc oc oc cc a a a ro r>- ro ro c cc r> cc h h vC c d- c\ C d" O CC 0 IT^OCO^vDCvOlf. vCOCMTOK »-i CC Lrr^f^r^cecccocccoco tn rO rO cc cc co x ro r> -h r- 3- r> r> X) vc d- - ro K ro k. ro ro ro to ro to re re ro re K* re ro ro ro k~ ro ro ro — cc or oC' cc cc cc cr cc- oc- cr cc cc cc cc cc cc cc or cc cc cc cc oc >- < rorororororororopororororororororororororororo % ooooooooooooooooooooooo J orOOfOarOOfOoroopOOOaroofOOfOOfOo <~ r^^cMc\jroroj-d-LncnvCvcr--r^cccocrooo^^ic\j j. HW^HHrHHHHHHHHHHHHW(\J(\)(VC\l(\l 1258 en 4-1 CO 3 i oocoooccooo ooooooooo 3 :> cr ^ cr u UJ \ cr «-i :_ o •£ ro CV c c; c: ^ cc f^ (Y cr If; O tf IH O o cr cf v£ vC cr. cc a. oc co cc or cc r- r- vc 6 a u H w ex. > h- OOO fO(\](MvO vDO^COvDCCd-h-OO C5^(C »— ( 0" ct If! h- r- v£ r*~ a cc cc a CC CC fO vC lf> CO «-< r- v£ cr a. cr a a cr a «£; c? U t- ■y Y— 1 K CCL" vC C C Cd"£ i/) if. h h cc f- CC CC CO CD CC CO CO if CT CC >- to ir. m tc ro rc rc rr fo rc rc re i*~ k k k k . rr rrs f cccccc-cccocc. cccccfcc-cccocccccfercccccccC' ^c?-crcJ-^ cf J- i J 3 C cJ-cfcf^-^rt-ct-c}-^ l£ oooooooooooocoooocoo — - o^ofloiooiooiooioo'CciooioofO c c\j cm ro rO cr cr if. if \C <£, Is- Is- oc cc o- o ■ c o «■-< ^ 1259 m 3 > ooooooooooooooooooo IT £ IT O Li! "N CC cr o o h- vcs o r> c 13 0 sc o e r-i vc vc < 2 ►J w > LlJ O «H CDvDC^O OOO0V^(CvCOfHNOr4d f«~. CC, rOvCh- r-CC^CLT! KjCOOOCM cc cc a cc cc cc cc cc h h vr. vt coCcCcrvCOf^Och-^cea h if, tr vC c\j .c r- r- cc x x x r~ cccccccocccocc coco CM 1^ PO 03 -1 CO Is- h- vO vD PL, < >- ro rc re re ro r. rcmrcfrcrorororororoirro r-r-f-f^r^-h-r-r-r^f^h-r^r^-r^r^r^r-r^r^ cr cc cc cc co cc cc- cc co co cc 00 cc cc a1 cc cc oc cr < trinmiririrLrinirLnmLnminir in in in in ooooooooooooooooooo oroorooroofoomomorooroopoo c\iC\ir,«i^u)invD\C^Ncccoj'^ooH __,^r-I^H.H.HrH.H.-l^^.-t.H.-I^C\JC\|C\J 1260 vO w 3 60 3 < Z5 ooooooooooooooooooooooo LT o uj \ rr v& o »-i it c > ro r- ct ex, o a ■ «h 3- Kj r- oc cc cc cc or r- r^r^r^ir cv t— i o o c «-< c (\iO,rtaO'Mrioifirtec,cccir-vCc :£ cr Lu >- r^aocMctvor-r^cococor^vOfOoaj h-r-cc'cococccococccccooccocch- o o> vD c}- K" rr k~j k i«". k rr k. r^ K' f*" f; K ro K~. re k K K" r f. k r^ 2 cccccca'cccr, cccccccccr, cccccrccororcrcfcfcrcrcr;: vO\CvCvCvCvO«JDvCvCvDnCvCv£vCvC^CvCvDvCvC'vCv0vC 5 cocooooooocooooooocoocvjro ■~t orOOiOOrOOfOOrOorOOfOO.-OorOO'Oomo 1261 CO On OOOOvOvOOO CMvOvOOOmo^-vOOOOO vD Is- oc cc 0 CO CC 01 CO CC in CO co r» ?. IT CLCOGCVjvOCO OCC'(\l(\lC'l/)3'OCCOCO 3" v£ cc cc cc cc Is- <,c fo -* > i-. ^ IT LL OOOlOOvPOM »-^OCOc)-vOlOvD^-CVjrOr^C5sO >- 3 Cf Is- CC o o>oO'ccircv^-,or--crro o crccr. acraccoc^vDvO H (C O Ct- O C C C OOCCOOOCCCOCvJfOO jT i/1 O !0 Is- Is- CC CO rO CM vO Is- ^O cf f~ ■ m tc f re • k r, K **" k it k, r, k k ic io k r. io k oc cr - Is- Is- Is- r-- Is- Is- Is- r^r^i^-r-r-h-i^r-i^h-f^r- Is- OOOOOOOO OOOOOOOOOOOLOO cv t\i ro ro cj- ;* in iT' ^vOr-h-cccLO^o^oo^^HCM tH^»-( -IHHH- ( HHHHHHrtHC\lf\|(\Jf\|(\J 1262 C* 00 CO 3 I < w 3 > IT O UJ \ en *: < Llj >- ooooocfctooooooooooooo -ho Is- Is- Is- Is- coo»-toocoocococ&oooco J- CNOOONOOOOONOtOiDHOtCOOMCvO x c - cc cc a. cc cc cr cc cc cc. cccccccccr. cccccocccc cc c: oooooooooooooooooooc Z) POOiOorOorOOrOorOorOorOorOorOa c »- o o o o o o o • •••••• o O c c O- O o o • •••••■ < o ►J w > OOeif)MNH »— ( 2 Co in cc »h id cJ- - ro m rO K~ K> K. K" Is- Is* Is- r* r- h- r> cc cc cc cc cc cc cc >- cr a a a a O" c o o c o o o o O fO O rO rO tO K) H H H H rH C\l (\J 1264 en 4-1 3 3 3 > oooooooooooo \ cr oocooocc occc ^c < H p pa w @ o H iJ W > U OOOh-i-OO^OOOOOO CV d- IT IT' v£ OOCC CC ""CO 10 CV IT- «-i vC 3" cX3^HvC«-t'DCrc0roas^ 5H PL, ro ro ro ro ro K ro ro ro ro r<" ro r-r*-r-r^r-r-r-r^r-r-is-r>- ac cc co cc co cc cr tr cr cc cr cc >- o o o o c o cr O O c c c cooooooooooo coorOOfOOrOoorOrO 1265 Appendix C. Pyrgeometer data 1266 PYRGEOMETER DATA August 6, 1973 Ship KRENKEL RESEARCHER Sensor no, 11540 LJ, (mw/cm ) (°C) L* (mw/cm ) 0200 0205 0210 0215 0220 0225 0230 0235 0240 0245 0250 0255 0300 0305 0310 0315 0320 0325 0330 0500 0505 0510 0515 0520 0525 0530 0535 0540 0545 0550 0555 0600 0605 0610 0615 39.8 26.6 39.6 26.7 39.8 26.7 39.9 26.5 40.6 26.4 39.9 26.4 39.9 26.4 40.1 26.4 39.9 26.4 39.8 26.2 39.9 26.3 39.9 26.2 39.9 26.3 40.2 26.5 40.0 26.8 40.3 26.9 40.4 26.5 40.3 26.6 40.8 26.5 39.2 26.2 39.4 26.4 39.0 26.1 38.9 26.2 39.3 26.4 39.6 26.3 39.6 26.0 39.7 26.0 40.0 26.2 39.9 26.2 39.8 26.2 39.8 26.2 39.4 26.0 39.9 26.3 39.7 26.1 40.1 26.2 40.3 40.1 40.1 40.4 41.2 40.5 40.2 40.6 40.4 40.4 40.2 40.5 40.6 40.8 40.3 41.1 41.1 40.7 41.5 40.0 40.0 39.9 39.8 40.0 39.9 40.3 40.5 40.4 40.4 40.1 40.1 40.1 40.3 40.1 40.5 1267 &J2SS** r/WfNT Of U.S. DEPARTMENT OF COMMERCE Frederick B. Dent, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Robert M. White, Administrator ENVIRONMENTAL RESEARCH LABORATORIES Wilmot N. Hess, Director NOAA TECHNICAL REPORT ERL 300-OD 12 Environmental Research Laboratories Radiation Programs - Requirements and Recommendations KIRBY HANSON, Editor, Atlantic Oceanographic and Meteorological Laboratories EDWIN FLOWERS, Air Resources Laboratories GARY HERBERT, Air Resources Laboratories DOUGLAS HOYT, Air Resources Laboratories PETER KUHN, Atmospheric Physics and Chemistry Laboratory SYUKURO MANABE, Geophysical Fluid Dynamics Laboratory RUDOLF PUESCHEL, Atmospheric Physics and Chemistry Laboratory LOIS STEARNS, Atmospheric Physics and Chemistry Laboratory BOULDER, COLO. May 1974 For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 20402 1268 CONTENTS Page 1. SUMMARY 1 2. ATMOSPHERIC AEROSOLS 2 2.1 Aerosol Time-Series Measurements 4 2.2 Measurement Accuracy 4 2.3 Present Turbidity Measurement Networks 7 3. ENERGY BUDGET - SOLAR (0.3 - 3.0 um) 7 3.1 Regional Air Pollution 7 3.2 Ocean Heat Transport 8 3.3 Ocean Atmospheric Heat Exchange 11 3.4 Atmospheric Absorption and Scatter 12 3.5 Ocean Attenuation 14 3.6 NWS Solar Radiation Network and Other Radiation Measurements 16 4. RADIATION IN NUMERICAL PREDICTION MODELS 18 5. RECOMMENDATIONS 18 6. REFERENCES 19 1269 ENVIRONMENTAL RESEARCH LABORATORIES RADIATION PROGRAMS - REQUIREMENTS AND RECOMMENDATIONS 1 . SUMMARY This report describes both the scientific aspects of the Environ- mental Research Laboratories (ERL) radiation programs and the require- ment for measurement accuracy in these programs. The discussion in the following sections shows there are now requirements for accuracies which exceed present instrument technology. Table 1 summarizes the accuracies required. The term accuracy has been used in this report for ease in communi- cation. It means reproducibility to a known radiation scale value. It is not essential that this scale be the absolute radiation scale, but rather an established scale that does not change and is reproducible. At present, the International Pyrheliometric Scale (IPS) is the internationally accepted radiation scale for pyrheliometric measurements. The scale is maintained by the World Meteorological Organization (WMO) sponsored World Radiation Center in Davos, Switzerland. This scale is reproduced in the United States by the Engineering Division of the Na- tional Weather Service (NWS), and the Eppley Laboratory. Presently, there appears to be a discrepancy of about 1 percent in the IPS depend- ing on the type of standard used to define it. This discrepancy was determined only recently and is inherent in the definition of the IPS. In the past few years, new types of absolute pyrheliometers have been produced by Kendall (1969), Will son (1973), and Geist (1972). These instruments promise to be useful absolute standards. The ERL radiation scientists have been obtaining the Eppley Labora- tory radiometers with calibrations linked to the IPS. As a result, pre- vious ERL radiation measurements are traceable to the IPS through Eppley Laboratory standards. In a few cases, however, some research studies have used data from NWS network instruments, which have calibration traceability to the IPS through NWS standards. Recent studies show a discrepancy between the NWS and Eppley Laboratory pyranometer standards of 3.5 percent and in some (explainable) cases 10.5 percent (Hanson et al., 1974). 1270 Table 1. Aceuraey Requirements for ERL Radiation Studies Stud ies Atmosphere Turbidity Regional Air Pollution Ocean Heat Transport Ocean Atmosphere Heat Exchange Atmospheric Absorption and Scattering Oceanic Attenuance Pyrhel iometer Pyranometer Time (%) (*) Scale 0.5 decades 0.5 months 0.5 years 2.0 months 0.2 mi nutes 2.0 months Present program requirements for accuracy (such as 0.5 percent over a period of decades) for the Geophysical Monitoring Program cannot be met by present instrument technology and measurement methods. Support for other ERL programs will require a great deal of effort by laboratory per- sonnel to maintain a known radiation scale, to calibrate working stand- ards and field radiometers, and to establish filter and sensor character- istics. Even with an extensive effort, it is uncertain that accuracy requirements can be met in all cases. In view of the present need for laboratory support of ERL field pro- grams, it is recommended that: 1. A central radiation facility be established to: a) maintain (national) primary standard radiometers (with established calibration traceable to the internation- ally accepted pyrhel iometeric scale) and provide facil- ities for calibrations of working standard radiometers; b) provide facilities for evaluating commercially avail- able pyrhel iometers and pyranometers; c) provide facilities for evaluating detectors, filters, and energy sources so their characteristics are known; d) provide facilities for developing new sensors to im- prove the absolute accuracy and reproducibility of present radiation measuring instruments. 2. Such a central radiation facility be responsive to the techni- cal needs of both the network programs of N0AA and the indi- vidual ERL radiation measurement programs. 2. ATMOSPHERIC AEROSOLS At present, there is much concern about what man is doing to the environment and where this may lead. One concern is the climate. 1271 We know that in the earth's history the climate has changed on many time scales, and various theories have been advanced to explain these changes. These theories involve variations in the sun's radiation, the earth's orbit, the circulation of the oceans, and the composition of the atmosphere. Although these variations occur naturally, some have re- sulted from man's activities. Since the beginning of the 20th century, man has greatly increased his burning of fossil fuel. This has caused a steady increase in the carbon dioxide (C02) concentration in the atmosphere. There is also some evidence that this burning has increased the concentration of atmo- spheric aerosols over some areas of the earth. Because both C02 and aerosol particles have a significant influence on the radiation balance of the earth, there has been much concern about the effect these in- creases may have on the climate. There are many natural sources of aerosol particles in the atmo- sphere. The continents inject aerosols by volcanic eruptions, dust storms, and photochemical reactions involving trace gases and plant hy- drocarbons; ocean areas contribute salt particles from the evaporation of ocean spray; and man releases aerosols by the solid particles of com- bustion and photochemical reactions of combustions products. Because they act both as condensation nuclei for water molecules and as freezing nuclei for supercooled water droplets, aerosols play an impor- tant role in the atmosphere. This characteristic of aerosols leads to a reduced lifetime in the atmosphere. In the lower atmosphere, the average lifetime is from days to weeks, because of precipitation processes and fallout. In the upper atmosphere, the lifetime is from months to years. The eruption of Mt. Agung on Bali in March 1963, exemplifies the ef- fect of a stratospheric aerosol layer on the temperature of the atmosphere. Within a few months following the eruption, temperatures in the tropical stratosphere rose 6 to 7°C and remained 2 to 3°C above normal for many years. Although observations are unavailable for earlier major eruptions, such as Mt. Tambora (1815) and Krakatoa (1883), the visible display of twilight colors that were observed leaves little doubt that major volcanic eruptions influence solar radiation attenuation and stratospheric heating for a number of years after the eruption. A difficult problem of geophysi- cal monitoring programs is to determine the changes in atmospheric attenu- ation due to man's activities against a background of natural variations in turbidity such as those resulting from volcanic eruptions. Air molecules scatter and absorb sunlight in a predictable manner. Aerosols also scatter and absorb sunlight, but their shapes and optical characteristics complicate an evaluation of these terms. With calcula- tions of the effect of air molecules, atmospheric attenuation measure- ments can be used to determine that amount caused by aerosols alone. Some time-series measurements of total atmospheric attenuation are now available; they indicate the long-term trend of the amount of atmospheric aerosol . 1272 2.1 Aerosol Time-Series Measurements Radiation measurements on Mauna Loa, since the International Geo- physical Year (IGY) in 1958, show a change in turbidity resulting from the Mt. Agung eruption and its subsequent return to normal turbidity levels (Pueschel et al . , 1972). The measurements (fig. 1) are based on an analysis of broadband radiation intensity data at Mauna Loa. The upper curve is a fit to the data during the pre-Agung eruption period 1958-62; the lower curve fits the data for 8 years after the eruption and indicates a return to normal aerosol concentration in the tropical stratosphere. These results show that no long-term trend in strato- spheric aerosols related to man's activities can be distinguished. Measurements at the South Pole Station, Antarctica, beginning dur- ing the IGY, also show the effect of Mt. Agung aerosol (Viebrock and Flowers, 1968). The broadband solar radiation intensity data (fig. 2) show that 9 months after the eruption of Agung, the aerosols reached the South Pole stratosphere. The data a few months later, early 1964, show the strong attenuation caused by the aerosol, which reduced the direct-solar intensity to only 20 to 30 percent of its value prior to the Agung eruption. During the subsequent 2 years, the return toward pre-Agung levels is apparent. The advantage of this South Pole site is that measurements with long atmospheric path lengths are easily obtained and that tropospheric variables have minor influence on the measurement of stratospheric turbidity. Such sites are extremely rare. Measurements in Europe and North America (Budyko, 1969) show that solar radiation penetrating the troposphere and reaching the earth's surface decreased by 2 percent per decade. This decrease is believed to be associated with an increase in industrialization on these conti- nents. Measurements of turbidity at Davos, Switzerland, show that the Ang- strom turbidity coefficient, 3, increased from 0.024 to 0.043 during the 38 years from 1920-1958 (McCormick and Ludwig, 1967). This increase in aerosol concentration reduced visible sunlight 2.8 percent per decade. 2.2 Measurement Accuracy At the Mauna Loa Observatory, eight pyrhel iometers have been used since 1958 in the program to determine long-term turbidity trends. Even though the instruments were calibrated by either the manufacturer or the government laboratory responsible for maintaining the national standards, and despite some direct intercomparison of instruments at the observatory, there are unresolved differences in the base calibration of different sen- sors. The largest difference was near 6 percent; this made the use of absolute intensity values impossible for evaluating trends (Pueschel et al., 1972). Unfortunately, these erroneous data were published by N0AA 1273 MAUNA LOA SOLAR RADIATION T_ ' ■ r~\ I ' I 1 1 | 1 I 1- 1 1 J— 1 1 |. T f- "1 ' r— T-1 r_1 r i i i i i i i i — i i i i i i i l l l — i I i — r- '™ £ £ A & ' ' ' M ,1h ik jan"" '■■'■■ -'. 1958 1959 i960 1961 JUL 1962 I I I I I I [ 1 IT I I | I I I I I | I | | | | ! | | | | | [ | | ! , | | ! ~1 — I I 1 — I — i— I — i — i— i — i — I— r- ,l~L-'1' ' ■ ', i i 'i i rv i ■ i i wr i i . ■ ■ ■ i ■ ■ t ■ ■ i iT1-"?' i i ,T r ,A" JUI- JAH JW-. JAM JUL. JAN. JUL JAM. JUL JAM, 1963 1964 1965 1966 t967 I ' ' ' I I I i ' i I i I i i — i i i | i i i i i | i i i i — r— p ' ' ' 'fri,,' ' ' ' ' ■• I I r | l l l I l | ' ' ' ' ' I i i 1 1 1 — i — J i i i i i i ' iiii L!°y -1 I 1_1 ■ ■ I I I I I I I I u JUL JAM JUL JAM. JUL JAN. JUL 969 1970 1971 1972 Figure 1. Transmission factors (dots) and least squares approximation (solid curve) for the pre-Agung eruption period (Jan. 58-Feb. 63) and the post-Agung eruption period (Apr. 63-Dec. 71) (after Pueschel et al.3 1972). in the Climatological Data3 National Summary. Peterson and Bryson (1968) subsequently used these data and, because of the error in absolute val- ues, came to the incorrect conclusion that a systematic increase in tur- bidity had occurred at Mauna Loa. The Mauna Loa solar radiation intensity values have been reevaluated by Ellis and Pueschel (1971) and by Pueschel et al . (1972) who used only the relative intensity values. Although this method of transmittance calculation (which involves the ratio of two intensity values) is useful 1274 ~i i r 60 40 30 AIR MASS 20 20 n i i i 30 40 60 DEC. 1, 1964 DEC. 8, 1963 "l 1 Figure 2. Direct solar radiation data for Amundsen- Scott (South Pole) Stations j Antarctica (after Viebroek and Flowers 3 1968). for determining long-term changes in atmospheric transmittance, it is not a quantitative measure of turbidity as are the classical turbidity terms. The important question that must be answered concerning geophysical monitoring is: what measurement accuracy and what time period is re- quired to resolve a long-term trend to a certain resolution? If we ap- ply the turbidity trend problem to this question, we have the following result. If we assume a change in radiation intensity of 2.8 percent per decade, based on Davos data (McCormick and Ludwig, 1967), and assume a need to resolve this change to one part in 10, then an 0.5 percent ac- curacy in long-term series of measurements will require 18 years of data to obtain the necessary resolution of the trend. Similarly, an accuracy of 1.0 percent will require 36 years of data in order to obtain the spec- ified resolution. Angstrom's turbidity factor, a, also critically depends on the ac- curacy of the intensity measurement. For example, with an instrument accuracy of 0.5 percent, it is possible to resolve a only to about 50 percent, in the normal range of values. The turbidity factor a is use- ful because it provides a single index measure of the size distribution of the aerosol particles. Use of the word accuracy is a problem in semantics. For a long- term geophysical monitoring program, it is necessary to reproduce the same radiation scale in a series of instruments to be employed over a 1275 long period of time. This is commonly termed reproducibility rather than accuracy. Because the present radiation scales are reproduced by radiometers rather than fundamental properties, it is possible for these scales to change with time. At present, there is a discrepancy in the International Pyrhel iometric Scale (1956) of approximately 2h percent, depending upon the type of standard used to reproduce the scale (Frohlich, 1973). 2.3 Present Turbidity Measurement Networks The Geophysical Monitoring program of ERL has plans to establish six baseline stations for measuring radiation. Stations are now in op- eration at Mauna Loa, Point Barrow, Alaska, and Boulder, Colorado. At each of the stations, 13-channel spectral pyrhel iometers and four spec- tral pyranometers will be operated. The geophysical monitoring program will maintain standard pyrhel iometers and pyranometers for calibration of the field sensors. A World Turbidity Network was started by ARL/ERL in the 1960's. The network includes 90 stations and obtains turbidity measurements at 0.50 ym wavelength (and at some locations 0.39 ym) using Volz-type sun photometers (Volz, 1970). The Division of Meteorology, Environmental Protection Agency, Raleigh, N.C., maintains working standard photometers that are used to calibrate the network photometers. The National Cli- matic Center, N0AA, evaluates and publishes the data. 3. ENERGY BUDGET - SOLAR (0.3 - 3.0 ym) 3.1 Regional Air Pollution When structures are grouped in cities they modify the local climate. The term "climatological dome" has been used to describe this modifica- tion (Peterson, 1968). A regional air pollution study in St. Louis, Mo., showed that during the summer, urban produced particulates in the atmo- sphere caused differences in total solar (sun and sky) radiation between urban and nonurban areas of St. Louis of 2 percent. If this difference is to be resolved to one part in four, then the accuracy of the instru- ments must be 0.5 percent. When spectral irradiance of sun and sky is measured with hemi spher- ically filtered pyranometers, there is a critical need to match filter characteristics of instruments used in urban and nonurban areas. Tests on filters have shown that a 6-nm shift in cutoff wavelength can cause a 4 percent difference in spectral irradiance determination. Clearly, 1276 this difference is larger than the urban-to-nonurban radiation difference that must be measured. This shows the need for carefully evaluating fil- ter studies. 3.2 Ocean Heat Transport The annual average solar radiation at the top of the earth's atmo- sphere on a surface normal to the sun's rays is 1.95 cal/cm2/min (Drummond, 1970). Distribution of this energy over the planet depends on two param- eters: the earth-sun distance and the local elevation angle of the sun. The first parameter causes a yearly variation in solar radiation of ±3.3 percent; the second causes the well-known variation of solar radiation with latitude. The atmosphere is a great heat engine that derives its source of energy from the large difference in solar radiation absorbed in the tro- pics as compared with the polar regions. The atmosphere has a partial control on the earth's absorption through variations in the amounts of clouds, aerosols, and polar ice that are present. In the 1940' s, ab- sorption by the planet was estimated at about 60 percent. However, sat- ellite measurements in the past 10 years have shown that the absorption is actually about 70 percent and that the difference between earlier estimates and present measurements mainly occurs in the tropics. There the absorption is higher than previously thought. Although seasonal variations in the planetary net radiation have been measured by satel- lite, annual variations are less than the error of present satellite measurements (about 3 percent); therefore, the annual variations cannot be resolved (Vonder Haar, 1972). Although investigators disagree somewhat, the planetary radiation budget shows that of the solar radiation reaching the planet, 22 percent is absorbed directly by the atmosphere, 45 percent is absorbed at the earth's surface, and 33 percent is reflected into space (London and Sasamori, 1971). In the infrared portion of the spectrum, terrestrial radiation loss at the earth's surface is equivalent to 15 percent of the solar radiation reaching the planet, and atmospheric infrared loss is equivalent of 52 percent. Thus, the earth's surface has a surplus of 30 percent and the atmosphere has a deficit of 30 percent of the solar radiation reaching the outer atmosphere. Clearly, the earth's surface is a heat source and the atmosphere is a heat sink. Satellite measurements of solar and infrared radiation confirm the pre-satellite theoretical calculations that show there is net radiational heating in the tropics and cooling at higher latitudes. This imbalance means that, temperatures could not remain at present levels without heat from the tropics being transported toward polar areas, which confirms the existence of meridional transport of heat by the oceans and atmosphere. Various techniques have been used to estimate this transport. 1277 From the principle of conservation of energy, we can determine the radiative energy gain or loss in a vertical column of atmosphere and ocean by knowing the horizontal transport of heat from that column. Furthermore, if we have some knowledge of the vertical distribution of radiation, temperature change, and other heat exchange processes within the column, we can evaluate the vertical distribution of horizontal heat transport as well. When this principle is applied to the atmosphere and ocean, the radiation components at the ocean surface and satellite height together with the latent and sensible heat components at the ocean sur- face can be used to calculate the separate heat transports by the atmo- sphere and ocean. Although the worldwide grid of atmospheric sounding stations pro- vides an adequate means of directly determining atmospheric heat trans- port, this approach is not possible for the ocean because of the lack of adequate data. To determine ocean heat transport, we must use indirect methods, such as that of residual energy calculation based on conserva- tion of energy. Oceanic heat transport has been estimated by several investigators and considerable disagreement exists. Studies of the heat and moisture balance of the earth have been con- ducted by many investigators. Budyko (1956 and 1963), whose work is widely accepted, is quoted here. Because solar radiational heating of the oceans is the largest com- ponent of the heat balance of the ocean, determining oceanic heat trans- port as a residual depends on the amount of radiational heating. Table 2 (from Budyko, 1956) shows how the heat budget components vary with latitude. Recent studies suggest that Budyko's (1956 and 1963) estimates of solar radiation incident at the ocean surface in tropical and sub- tropical latitudes may seriously underestimate the magnitude of this term (Quinn, 1968; Hanson, 1972). This suggestion is based on continuous solar radiation measurements for 8 to 11 years at three small tropical islands. These measurements indicate that in the equatorial dry zone and subtropical high pressure areas, solar radiation is 15 to 20 percent greater than specified by Budyko (1963); in cloudy regions such as the Inter Tropical Convergence Zone (ITCZ), the difference is less. Satellite measurements of cloud cover over a 2 year period have been used to extend the island station measurements to all tropical ocean areas from 30°N to 30°S (Hanson, 1974). The result indicates that 64 percent of the solar irradiance reaching earth at this latitude is transmitted through the atmosphere to the ocean surface. Budyko's estimate gives 51 percent. If we assumed the other heat budget components indicated by Budyko are correct, then the required oceanic heat transport given by Budyko would increase from 17 to 56 (xlO3 cal/cm2 year) for the oceanic latitude zone from 0 to 30°N. However, it is highly unlikely that heat transport by the ocean is actually that large; satellite measurements indicate the combined heat transport by ocean and atmosphere is about 31 (xlO3 cal/cm2 1278 Table 2. Mean Annual Distribution with Latitude of the Heat Balance Components of the Ocean Surface (after Budyko, 1956) Lat i tude Units: 103 cal/cm2 Year (°) Q+q R Qe <*s Qvo "North 60-50 88 34 34 18 -18 50-40 109 54 51 15 -12 40-30 136 78 73 12 - 7 30-20 151 100 85 7 8 20-10 156 110 89 5 16 10- 0 149 107 °South 76 5 26 0-10 152 107 81 7 19 10-20 155 107 97 9 1 20-30 147 94 87 10 - 3 30-40 128 73 77 12 -16 40-50 104 53 57 5 - 9 50-60 84 31 37 12 -18 Whole Earth 128 77 68 9 0 year) for that latitude belt (Vonder Haar, 1972). Thus, the additional implication of greater solar energy input to the ocean is that latent and sensible heat loss at the ocean surface also must be larger than Budyko's estimate. The pertinent information available on heat budget components has been combined in the right portion of figure 3; the left side shows Budyko's (1956) estimates. For the recent estimate, the la- tent and sensible heat loss terms are calculated as residuals; latent heat loss (112 x 103 cal/cm2 year) is 35 percent greater than that given by Budyko (1956). A knowledge of the solar radiation distribution over the world's oceans on annual and longer time scales is essential for indirectly de- terminating evaporation and poleward transport of heat by the oceans. On annual time scales, there is need for an accurate determination of solar radiation because the variability of mean annual irradiance is small. At tropical island stations, for example, the standard deviation of the mean annual irradiance is about 5 percent in the areas with least cloudiness. If we wish to resolve the year-to-year variability in solar irradiance to one part in 10, it will be necessary to have absolute ac- curacy of 0.5 percent. If small island station measurements are to be extended over larger space scales, satellite radiation or cloud measurements must be used. 1279 Budyko (1956) Hanson(1972) RT = 31 (AT =11) > 152 I 135 1 91 1 71 L 48+T12 + 11 Surface 46+83+6 Q+a IR+Qe+Qs Q+a IR+Qe+Qs (OT = 17)— * (0T = 20) — +> Figure 3. Mean annual heat transport, 0° to 30°N3 in Koal/cm2 year, as given by Budyko (1956) and Hanson (1974). Satellites also are limited in temporal and spatial sampling. Because of this limitation it will not be possible to use satellite measurements to extend the island measurements (of 0.5 percent accuracy) to other areas and maintain the same accuracy. Adequate studies of the limita- tion of temporal and spatial sampling by satellite are not now avail- able. The present satellite absolute accuracy is approximately 3 per- cent. 3.3 Ocean Atmosphere Heat Exchange Section 3.2 discussed heat exchange between the ocean and atmosphere on annual and longer time scales and on space scales the size of oceans. This section covers sea-air interaction studies on scales of hours and a few square kilometers. Studies by Stommel et al . (1969), Turner (1969), Delanore (1972), and Ostapoff (1972, private communication) indicate that radiation mea- surements at the ocean surface combined with oceanographic observations can be used to determine the sensible and latent heat exchange between the ocean and atmosphere on daily to hourly time scales. These investi- gators found that in tropical latitudes with normal trade wind conditions the radiative energy gain by the water is nearly balanced by the loss of latent and sensible heat. The small difference (usually < 10 percent) is a slight warming or cooling of the water column. A few exceptions to this exist, such as in the tropics where upwelling of cold water occurs. There, evaporation is limited and the sign of the sensible heat exchange is re- versed; under those conditions the difference between the gain and loss of heat is not small, and the water is warmed by sunlight much more ra- pidly. 1280 An analysis of the accuracy required to evaluate the various heat budget components shows that the most difficult term to measure is heat storage. Here a precision of 0.001°C is required for useful data accu- racy. The comparable accuracy in radiation measurement is 2 percent for solar radiation and 3 percent for net radiation. 3.4 Atmospheric Absorption and Scatter From a knowledge of solar radiation reaching the earth's outer atmo- sphere and from basic radiation theory, we can calculate the various ra- diation components within the atmosphere. Solar radiation modified as it passes through the atmosphere; scattering and absorption by atmospheric gases, aerosols, water droplets, and ice crystals all contribute to the attenuation. At present, it is possible to determine precisely radiation scattered by atmospheric gases (Sekera, 1956). It is also possible to determine relatively precisely, the absorption of solar radiation by at- mospheric gases from laboratory absorption spectra and radiation theory (Howard, 1959). Thus, the radiative properties of a pure gaseous atmo- sphere are well known and can be employed in numerical prediction model- ing to whatever precision is required. However, the scattering properties of a realistic atmosphere with aerosols, cloud droplets, and ice crystals are not well known, and of these variables usually only the effects of clouds are included in pres- ent numerical prediction models as simple approximations. The scatter- ing properties of aerosols depend on their shape, size distribution, and index of refraction. The global distribution of these variables is not known to a useful accuracy. Even less is known about the absorption properties of aerosols. Some measurements indicate that absorption var- ies widely, but in some cases it may be equivalent to the reduction of radiation due to scattering (Robinson, 1962). Because of their high reflectance, clouds play a major role in the scattering and absorbing properties of the atmosphere. These proper- ties vary depending on density and total depth of the cloud droplets. Thick cumulonimbus clouds in the tropics may attenuate more than 99 per- cent of the incident extraterrestrial radiation on a time scale of hours (Hanson, 1971). Of this amount, absorption probably does not exceed 25 percent of the incident radiation (Moller, 1964). Measurements and calculations of absorption in clear atmospheres have been compared. Measurements by aircraft over southern England in- dicate that atmospheric absorption is a factor of three higher than cal- culations based on water vapor, C02 , and ozone (03) absorption (Robinson, 1966). Measurements over the English Channel show similar results; the maximum instantaneous heating rate due to solar absorption was 5°C/day as compared with 1 to 2°C/day for calculations (Roach, 1961). Over a 1281 clear tropical ocean, measurements show instantaneous heating rates at 3°C/day in the dusty lower troposphere compared with 2°C/day for calcu- lations (Cox et al. , 1971). With cloudy atmospheres, determining absorption is even more diffi- cult. The first direct measurements of cloud absorption showed only 5 to 9 percent of incident flux for clouds 50 to 500 m thick (Neiburger, 1949). Subsequent measurements (Robinson, 1958; Fritz and MacDonald, 1951) showed absorption of 20 to 25 percent of incident flux for clouds of various thicknesses from less than 300 to 2,000 m. Satellite and sur- face measurements have been combined to determine atmospheric absorption with heterogeneous cloud distribution. For the United States, the results show that in summer absorption varies from 15 to 25 percent for water va- por optical path lengths of 2 to 6 cm (Hanson, 1971). Direct measurement of absorption of solar radiation in an atmospheric layer requires high precision because absorption is obtained by evaluating the small difference between the radiation impinging on and that emerging from a layer. Absorption over the entire vertical extent of the atmo- sphere may be as large as 25 to 30 percent of the incident irradiance. To resolve this atmospheric absorption to one part in 10 using combined satellite and surface radiation measurements, we must obtain measurements to 1 percent accuracy. This technique of combining satellite and surface measurements to obtain atmospheric absorption is most applicable on mon- thly and longer time scales because the representativeness of surface mea- surements is spatially limited, and this shortcoming is minimized on longer time scales. Greater precision is required for measuring solar radiation ab- sorption in an atmospheric layer of limited thickness, than for absorp- tion in the entire atmospheric col- umn. Measurements in moist, tropi- cal, relatively dusty air show that for the layer of 150 mb thickness above the ocean surface, the absorp- tion of solar radiation was 0.077 cal/cm2/min (5.4 percent of the in- cident energy) resulting in an in- stantaneous heating rate of 3.0°C/ day (fig. 4). The calculated heat- ing rate based on water vapor and C02 indicated a heating rate of 1°C/ day less than the measured value. If one wishes to resolve the differ- ence to 1 part in 10, a precision of 0.0025 cal/cm2 min is required. This is approximately 0.2 percent of the incident solar irradiance; obvi- ously, this is difficult to achieve. (cal/ cm mm 1.42 I 850mb L I-- 0.123 1. lOOOmb AT/At = 3.0(°C/day) O.IOO SURFACE Figure 4. Average upward and down- ward solar irradiance on 4 days in June and July 1969 in cloud- less sky condition near Barbados (Cox et al.. 1971). 1282 However, two measurement techniques with inherent advantages have been employed to obtain measurements to high precision. One technique is to use an aircraft with up-looking and down-looking pyranometers. By flying horizontal legs at various altitudes and where the radiation field is horizontally homogeneous, the instruments measure the vertical irradiance profile. The advantage is that radiation differences are ob- tained from a single sensor as a function of time, which removes syste- matic errors. A second measurement technique involves two aircraft, with up-looking and down-looking sensors, vertically separated in the atmosphere. Absorp- tion is obtained by taking measurement differences across the intervening layer. To minimize systematic differences, sensors can be compared by flying the aircraft together. Actual flight data collected in this mode indicate sensors agree in absolute value to 0.5 percent (Drummond and Hickey, 1970). Sensor accuracy under flight conditions should be stud- ied to determine whether the required 0.2 percent accuracy is possible. Perhaps instrument characteristics in flight are such that 0.2 percent accuracy is unattainable. This should be investigated. At present an accuracy of 0.2 percent appears to be the least possi- ble error, which implies that useful absorption data are limited to lay- ers near the qround and 150 mb thick, or greater, providing the layer has relatively high absorption. 3.5 Ocean Attenuance For heat budget and other applications, it would be desirable to calculate the angular and spectral distribution of the downward and up- ward solar radiation components in the oceanic photic zone. Although reasonably precise calculations are possible for pure sea water and a smooth sea-air interface, for sea water with particles and a rough sea- air interface, the calculations become \zery complicated. The scattering and beam attenuation properties of pure sea water show that water acts as a large particle scatterer, i.e., a large forward scatter (Duntley, 1963). The angular distribution of scattering by pure water (fig. 5) a log-scale plot, shows this strongly peaked forward scat- ter. This property means measuring the beam attenuation coefficient is difficult. Because an attenuance meter is designed to measure the atten- uation coefficient (the sum of the scatter and absorption coefficients), the strongly peaked forward scatter makes it impossible to build a meter to include the direct beam (non-scattered) component and exclude the scattered light component. In spite of this difficulty, direct-beam scattering and attenuation coefficients have been established (Clark and 1283 100,000 •" 1.0.000 - Figure 5. Angular distribution of ~ ' apparent radiance for different * distances from a uniform spheri- — 100 cat lamp (after Duntley, 1963). *■» o 10 -n — i — i — i — i — r_i — r ' ' i i i I i i i I I i i i i 1 L-^ I I I I 1—1 l—J I — L 15° 12° 9° 6° 3° 0° 3° 6* 9° 12° 15* James, 1939). These spectrally dependent coefficients show that the min- imum attenuation coefficient (a) occurs at 0.475 ym and has a value of 0.018 (nr1) for pure water, I7 = Ine -adz Here I0 and Iz are the direct beam intensities entering and leaving the layer dz. The difficulty of beam attenuance measurements has been overcome, for many applications, by obtaining spectral irradiance (2tt) measurements (e.g., Tyler and Smith, 1970). Spectral irradiance is the solar radia- tional energy passing through a horizontal unit area of surface, in unit time, in unit increments of wavelength, in either upward or downward direction. Such measurements show that the wavelength of maximum irradi- ance shifts toward 0.457 ym with increasing depth in clear water (fig. 6) this agrees with the spectral attenuance measurements. t r T r 2.0 2.2 h 24 Figure 6. The complete solar spectrum of downward irradiance in the sea (after. Jerlov3 1968). 1284 Because of the difficulty of operating spectrometers and maintaining high accuracy underwater, pyranometers with thermopile detectors have been used to measure spectrally integrated irradiance underwater. Such measure- ments are useful to determine relative changes (with time) of the transmit- tance of a water column. They are also useful for determining the absolute amount of energy reaching a specific depth and the heating rates in a water column. These determinations require an absolute instrument calibration. Because instruments calibrated in air require a correction when used under- water (the so-called immersion effect), an evaluation of the underwater correction is important. Underwater sensors with flat windows have a correction for the im- mersion effect of about 0.82 (slightly dependent on wavelength) (Tyler and Smith, 1970). Sensors with dome shaped windows have a correction of about 1.75 depending on wavelength and assumed model of the light environment (Gordon and Brown, 1972). The discussion in section 3.3 on ocean-atmosphere heat exchange showed that an accuracy of approximately 0.001°C in measuring ocean temperature is the limiting factor in studies of heat exchange between the mixed layer of the ocean and lower troposphere. To be consistent with this accuracy, an underwater pyranometer should detect the irradi- ance field within 2 percent of near-surface irradiance values. At pre- sent, it is doubtful that this precision can be achieved with hemi- spherical sensors underwater, because of the large correction (1.75) required for the "immersion effect" and the uncertainty about this value for various conditions and depths underwater. Further sensor develop- ment and tests are needed for a suitable underwater pyranometer. 3.6 NWS Solar Radiation Network and Other Radiation Measurements The National Weather Service (NWS) operates a solar radiation net- work for measuring solar radiation over the United States and a few tropical islands. The network includes 60 NWS and 20 cooperative sta- tions obtaining pyranometer measurements, four pyrheliometer stations, one net radiation station, and one ultraviolet radiation station. The network is managed by the Data Acquisition Division of NWS and the in- struments are calibrated and maintained by the Engineering Division of NWS. The sensors are calibrated by comparing them with primary and working standard radiometers that the Engineering Division maintains as national standards, which are traceable to the International Pyr- heliometric Scale (IPS) through international intercomparisons of the CIM0/WM0. Some of the pyranometers used at cooperative stations have been calibrated by the Eppley Laboratory, which also maintains standard radiometers with traceability to the IPS. 1285 NWS Network data have been used for studies of radiation over the United States which include (1) average solar radiation distribution on normal and cloudless days (Fritz, 1949; Fritz and McDonald, 1949); (2) evaporation and snow melt (Hydrologic Research and Development Labora- tory, NWS); and (3) solar radiation absorption in the atmosphere (Hanson et al., 1967; Hanson, 1971). The NWS network data at a few tropical island stations have been used to study the ocean heat transport and evaporation in tropical lati- tudes (sec. 3.2). Two problems have caused significant errors to be introduced in NWS radiation network data. The first is calibration. There is a systematic difference of 2.5 percent between the NWS standard pyranometer and the present IPS. In addition, in about 50 percent of the more than 1000 field instruments calibrated, an additional 7 percent error exists. Both errors cause measurements to be greater than the present IPS (Hanson et al., 1974). The second problem is degradation of field instruments in the net- work. The sensing surfaces of some pyranometers have degraded under strong sunlight and warm temperature, as shown in figure 7 (Case, 1973). This problem is found only with sensing surfaces coated with Parsons op- tical black paint, and the seriousness of the degradation varies from station to station. A loss in sensitivity of 15 to 20 percent has been found at some stations. Yeor Figure 7. Transmittance of the atmosphere at Albuquerque, N.M.3 based on NWS pyranometer measurements. Decreasing transmittance values indicate the degradation of pyranometer sensitivity. A new sensor (No. 2621) was installed in August 1967 and was replaced in March 1970 with a new sensor (No. 2276) (after Case, 1973). 1286 Numerous non-network radiation measurements have been obtained in research studies; for example, energy budget studies of regional air pollution (sec. 3.1); ocean atmosphere heat exchange (sec. 3.3); atmo- spheric absorption and scatter (sec. 3.4); and ocean attenuation (sec. 3.5). These measurements have been obtained in government and univer- sity research programs. In most cases, the radiometers were calibrated against Eppley Laboratory standards which are traceable to the IPS. 4. RADIATION IN NUMERICAL PREDICTION MODELS Radiation measurements are not used as input for numerical predic- tion models; radiation values are calculated in the model instead. How- ever, measurements are useful in verifying calculated radiation values. In short-range prediction models (a few days) of mid-latitude con- ditions, radiation is not an important term. It is calculated in a rel- atively unsophisticated manner in the model, and the error in radiation estimates has a minimal effect on prediction. In long-range prediction models (seasonal and longer), radiation becomes much more important and must be carefully calculated. That is, it must include the effects of radiatively active gases, aerosols, and clouds. The space scale on which local radiation measurements at the earth's surface are representative is usually much smaller than the space scale of radiation calculations in numerical prediction models. As a result, the use of surface radiation measurements to verify model calculations depends on extrapolating surface radiation measurements to larger areas. Similarly, satellite radiation measurements are space and time limited and do not have a one-to-one correspondence with the time and space scale of model calculated radiation. To date no studies are available on the degree of uncertainty which space and time limitation of surface and satellite measurements impose on verification of model calculations. Until such studies are complete, it seems reasonable that a 1 percent accuracy in pyranometer measurement be established as a necessary goal. 5. RECOMMENDATIONS There are various applications for pyranometer measurements in en- ergy budget studies. Each application has special requirements and dif- ferent accuracies. The most stringent accuracy is required for global energy budget studies (sec. 3.2), which must reproduce a radiation scale to 0.5 percent in a sequence of instruments used at a single station for many years. There is also a stringent requirement for short-term (few hours) reproducibility for direct measurement of atmospheric properties (sec. 3.4). Here the need is to maintain reproducibility to 0.2 percent under varying aircraft exposure conditions. 1287 To provide the necessary accuracies in radiometer measurements for ERL programs we recommend the following: 1. A central radiation facility should: (a) maintain primary standard radiometers (with estab- lished calibration traceable to the internationally accepted pyrheliometer scale) and provide facilities for calibration transfer to working standard radiom- eters of individual (ERL) laboratories. (b) provide facilities for evaluating characteristics of pyranometers, pyrheliometers, and filters used in en- ergy budget studies. This should include studies of the characteristics of all commercially available py- ranometers and pyrheliometers in the United States. (c) provide facilities for developing new sensors to im- prove the accuracy and reproducibility of radiation measuring instruments. 2. That such a central radiation facility be responsive to the technical needs of both the network programs of NOAA and in- dividual programs of the Environmental Research Laboratories. 6. REFERENCES ARWG (1972): Major problems in atmospheric radiation: An evaluation and recommendations for future efforts, Bulletin Amer. Meteorol. Soc. , 53(10): 950-956. Budyko, M. (1956): The Heat Balance of the Earth's Surface, Gidrometeoro- logicheskoe izdatel 'stvo, Leningrad, 255 pp. (Translated by Nina Stepanova; Weather Bureau, Wash., D.C., 1958.) Budyko, M. (Editor) (1963): Atlas Teplovago Balansa Zemnogo Shara, Glavnaia Geofizicheskaia Observatoria, Moscow. Budyko, M. I. (1969): The effect of solar radiation variations on the climate of the Earth, Tellus, 2(5) :611-619. Case, R. (1973): Use of true solar noon readings in quality control of the NWS solar radiation network, paper presented at the AMS Annual Meeting, St. Petersburg, Fl . , Jan. 29-Feb. 1, 1973. Clark, G., and H. James (1939): Laboratory analysis of the selective absorption of light by sea water, J. Opt. Soc. Amer., 29:43-55. Climatological Data, National Summary (1957-1967) , U.S. Dept. of Com- merce, ESSA, Environmental Data Service, Asheville, N.C. 1288 Cox, S., T. Vonder Haar, K. Hanson, and V. Suomi (1971): Measurement of absorbed short wave energy in a tropical atmosphere, 1971 Confer- ence of the International Solar Energy Society, Goddard Space Flight Center, Greenbelt, Md., May 11, 1971. Delnore, V. (1972): Diurnal variation of temperature and energy budget for the mixed layer during BOMEX, J. Phy. Oceano. , 2^(3): 239-247. Drummond, A. (1970): Precision radiometry and its significance in atmo- spheric and space physics, Advances in Geophysics, 14^1-52, Academic, New York. Drummond, A., and J. Hickey (1970): Total and spectral short-wave radia- tion measurement program on the NASA CV-990 Research Aircraft, BOMEX, July 1969, Final Report, Prepared for NASA, Goddard Space Flight Center. Duntley, S. (1963): Light in the sea, J. Opt. Soc. Amer. , 53^:214-233. Ellis, H. T., and R. F. Pueschel (1971): Solar radiation, absence of air pollution trends at Mauna Loa, Science, 172:845-846. Fritz, S. (1949): Solar radiation during cloudless days, Beating and Ventilating, 46(1): 69-74. Fritz, S., and T. H. MacDonald (1949): Average solar radiation in the United States, Heating and Ventilating, 46(7):61-64. Fritz, S., and T. MacDonald (1951): Measurements of absorption of solar radiation by clouds, Bulletin Amer. Meteorol. Soc, 32(6) :205-209. Frohlich, C. (1973): The relation between the IPS now in use and Smith- sonian scale 1913, Angstrom scale and absolute scale (paper pre- sented at the Smithsonian Radiation Symposium, Rockville, Md., Nov. 1973). Geist, J. (1972): Fundamental principles of absolute radiometry and the philosophy of this NBS Program (1968-71), NBS Tech. Note 594-1, 55 pp, Gordon, H., and 0. Brown (1972): Immersion corrections for the Eppley underwater pyranometer, Conference on Atmospheric Radiation, American Meteorological Society, Fort Collins, Colo., Aug. 7-9, 1972, pp. 163-168. Hanson, K. J. (1971): Studies of cloud and satellite parameterization of solar irradiance at the earth's surface, Proceedings of the Miami Workshop on Remote Sensing, NOAA/ERL, Boulder, Colo., pp. 133-148. Hanson, K. (1972): On the solar energy input to the world's tropical oceans, Proceedings 1972 International Radiation Symposium, Sendai , Japan. 1289 Hanson, K. (1974): A new estimate of solar irradiance at the earth's surface (to be published). Hanson, K. , J. Hickey, and W. Scholes (1974): The pyranometer calibra- tion program of the Weather Bureau, ESSA, and NOAA, 1954-72 (to be published as a NOAA Technical Report). Hanson, K. J., T. H. VonderHaar, and V. E. Suomi (1967): Reflection of sunlight to space and absorption by the earth and atmosphere over the United States during Spring 1962, Monthly Weather Review, 95(6): 354-362. Howard, J. (1959): The transmission of the atmosphere in the infrared, Proceedings of IRE, 47:1451-1457. Jerlov, N. (1968): Optical Oceanography, Elsevier, New York, p. 123. Kendall, J. M. (1969): Primary absolute cavity radiometer, Tech. Rept. 32-1396, Jet Propulsion Laboratory, Pasadena, Calif. Latimer, J. (1972): On the Angstrom and Smithsonian absolute pyrheliom- etric scales and the international pyrheliometric scale 1956, Pro- ceedings 1972 International Radiation Symposium, Sendai , Japan. London, J., and T. Sasamori (1971): Radiative energy budget of the at- mosphere, Man's Impact on the Climate, pp. 141-155, Edited by W. Matthews, W. Kellogg, and G. D. Robinson, MIT Press, Cambridge, Mass. McCormick, R. A., and J. H. Ludwig (1967): Climate modification by at- mospheric aerosols, Science, 156(3780) : 1358-59. Moller, F. (1964): Optics of the lower atmosphere, Applied Optics, 3:157-166. Neiburger, M. (1949): Reflection, absorption, and transmission of in- solation by stratus clouds, J. Meteorol. 6; 98-104. Peterson, J., and R. Bryson (1968): Atmospheric aerosols: increased con- centrations during the last decade, Science, 162:120-121. Pueschel, R., L. Machta, G. Cotton, E. Flowers, and J. Peterson (1972): Normal incidence radiation trends on Mauna Loa, Hawaii, Nature, 20:545-547. Quinn, W., and W. V. Burt (1968): Incoming solar radiation over the tropical Pacific, Nature, 217:149-150. Roach, W. T. (1961): Some aircraft observations of fluxes of solar ra- diation in the atmosphere, Quart. J. Roy. Meteorol. Soc. , 87:346-363, 1290 Robinson, G. (1958): Some observations from aircraft of surface albedo and the albedo and absorption of cloud, Arch. Meteorol. Geophys. Biokl. , B9: 28-41. Robinson, G. (1962): Absorption of solar radiation by atmospheric aero- sol as revealed by measurements at the ground, Arch. Meteorol. Geo- phys. Biokl. ,.B12: 19-40. Robinson, G. (1966): Some determinations of atmospheric absorption by measurement of solar radiation from aircraft and at the surface, Quart. J. Roy. Meteorol. Soo. , 92:263-269. Sekera, Z. (1956): Recent developments in the study of the polarization of skylight, Advances in Geophysics, 3/43-104, Academic, New York. Stommel , H., K. Sanders, W. Simmons, and J. Cooper (1969): Observations of the diurnal thermocline, Deep Sea Research, Suppl. 16:269-284. Turner, J. (1969): A note on wind mixing at the seasonal thermocline, Deep Sea Research, Suppl. 16/297-300. Tyler, J., and R. Smith (1970): Measurement of Spectral Irradiance Un- derwater, Gordon and Breach, New York. Viebrock, H., and E. Flowers (1968): Comments on the recent decrease in solar radiation at the South Pole, Tellus 20:400-411. Volz, F. E. (1970a): On dust in the tropical and midlatitude stratosphere from recent twilight measurements, J. Geophys. Res. 75:1641-1646. Volz, F. E. (1970b): Atmospheric turbidity after the Agung eruption of 1963 and size distribution of the volcanic aerosol, J. Geophys. Res. 75:5185-5193. Vonder Haar, T. (1972): Natural variation of the radiation budget of the earth-atmosphere system as measured by satellites, Conference on Atmospheric Radiation, American Meteorological Society, Fort Collins, Colo., Aug. 7-9, 1972, pp. 211-220. Will son, R. C. (1973): Activity cavity radiometer, Applied Optics, 12(4):810-817. 1291 ftGPO 1974 — 784-577/1271 REGION NO. 8 570 JOURNAL OF THE ATMOSPHERIC SCIENCES Volume 3' The Mechanism of Ice Crystal Growth and Habit Formation Dennis Lamb Desert Research Institute, University of Nevada System, Reno S9507 William D. Scott1 Sen-Air Interaction Laboratory, AOML, NOAA, Miami, Fla. 33149 (Manuscript received 26 July 1973, in revised form 1 November 1973) ABSTRACT The formation of multiple layers of adsorbed water molecules on the basal and prism faces of ice may be responsible for the remarkable temperature dependence of all growth variables (linear growth rate, step velocity, and mean migration distance). This effect results from an increased residence time of molecules in the adsorbed state as the melting point is approached. A quantitative treatment based on the Brunauer, Emmett and Teller model of multi-layer adsorption exemplifies these concepts and appears to explain the measured trends with temperature. When the theoretical treatment is used in conjunction with a growth model based on the propagation of spiral steps, reasonable values for the condensation coefficient emerge. The alternation of the primary habit of ice crystals with temperature is explained when the theoretical treatment is applied to the basal and prism faces, respectively. 1. Introduction Understanding the mechanism by which individual molecules ultimately become members of a crystal lattice is a basic goal of all crystal growth studies. The growth mechanism is the total picture of the growth process which gives physical meaning to growth data. When correct, it enables us to extrapolate the available data to other, more general sets of conditions and thereby to serve as a prediction tool. In addition to providing a detailed description of events on a particular crystal face, the molecular mechanism of growth is also the basis for the formation of the macroscopic crystal habits, since the habit is nothing but an in- tegration of the relative growth rates of the individual faces. In building up the macroscopic crystal, interac- tions arise between the microscopic surface processes and the macroscopic geometry of the crystal due to the limited rates of mass and heat transfer through the en- vironment. These interactions produce a wide variety of intricate crystal forms, characteristic of ice crystals grown naturally. The mechanism by which water vapor molecules become incorporated into ice crystals is important in atmospheric precipitation processes and has been in- vestigated by many from several points of view. Indi- vidual ice crystals have been grown artificially in the laboratory and collected in the real atmosphere; their habits and rates of growth have been measured as 'Present affiliation: Department of Environmental Sciences, Tel-Aviv University, Israel. functions of the growth temperature with the intention of formulating some generalities regarding the growth process. In light of recent measurements of the linear growth rates of individual basal and prism faces (Lamb and Hobbs, 1971 ; Lamb and Scott, 1972), it is possible to develop a coherent picture of ice crystal growth which satisfies much of the presently available data on the growth of ice from the vapor phase and which is, more- over, consistent with our general concepts of surface structure and the growth of other substances. The general features of previous investigations may be broken down into studies of habit, studies of growth rates, and studies of step parameters. Nakaya (1954) showed that the habits of ice grown in air are a compli- cated function of supersaturation and temperature. However, Kobayashi (1961) found that these varia- tions in shape may be subdivided into two broad classifications: primary habits, which depend mainly on temperature; and secondary features, which are strongly dependent on supersaturation. The secondary features appear superimposed upon the basic primary habit in the presence of external diffusion fields con- taining strong gradients of moisture or temperature. A peculiar characteristic of ice is the tendency for the primary habit to alternate'between plates and columns as the temperature is lowered from the melting point; the transition temperatures are roughly —4, —9 and — 20C. This alternation of the primary habit is a manifestation of the strange dependence on tempera- ture of the linear growth rates of the individual faces. Indeed, the works of Lamb and Hobbs and of Lamb 1292 March 1974 D I \ \ I [..Will AND WILLIAM I) . M "t>| I 571 and Scott present measured values of the linear growth rates which show these alternations in terms of maxima and minima in the growth curves. It should be realized, however, that it is only the relative growth rates which are of concern in under- standing the origins of the primary habits. A con- venient measure for the relative rates is the condensa- tion coefficient a defined bv where G,nax=QSF (1) (2) is the maximum growth rate possible at the net im- pingement flux 5/\ and V. is the volume of a water molecule in the lattice. The net impingement flux is related to the local supersaturation 5 by j=- SF (3) where FS(T) is the molecular flux hitting the surface at equilibrium. If bP is the corresponding excess vapor pressure, then from the kinetic theory of gases 8P 6F = (lirmkT)* ■=kTbP, (4) in which k is Boltzmann's constant, kr is defined as the kinetic theory factor, m is the mass of a water molecule, and T the temperature. From these equations the condensation coefficient can be calculated from linear growth rate data at known values of temperature and excess pressure (supersaturation). The trends with temperature so obtained from the data of Lamb and Scott are shown in Fig. 1. The overall trends to these curves are, of course, similar to those of the linear growth rates and cross at the temperatures ( — 5.3 and — 9.5C) which define the transitions between the primary habit regimes of plates and columns within the data range (Lamb and Hobbs, 1971). The condensation coefficient may be interpreted as the fraction of impinging vapor molecules which are successful at actually being incorporated into the ice lattice. The trends of Fig. 1 thus show how strongly the probability of incorporation varies with temperature on the basal and prism faces of ice. As indicated by Lamb and Hobbs, it may be just these strong variations in the crystallographic growth parameter a which give rise to the peaks in the rate at which an ice crvstal accumulates mass (Hallett, 1965; Fukuta, 1969). Of particular interest, too, is the tendency for the condensa- tion coefficient of both faces to approach unity as the temperature approaches OC, the melting point of ice. The condensation coefficients for the two main low- index faces of ice (prism and basal) do "explain" many aspects of the observed crystal habits and mass growth rates, but, even so, the physical basis behind the peculiar trends in the condensation coefficients them- PRISM FACE 1.0 - 0 5 -10 TEMPERATURE CO FlG. 1. The condensation coefficient of ice calculated from the linear growth rate data of Lamb and Scott (1972). selves remains to be uncovered. As pointed out by Lamb and Hobbs and discussed in detail by Lamb and Scott, there exists a basic similarity in the shape of the trend to the linear rates (or condensation coefficients) and the measured velocities of step propagation across the basal face (Hallett, 1961; Kobayashi, 1967). This, it was suggested, implies an indirect correlation be- tween the step velocity v and the frequency/ at which steps are generated on the face since the step velocity v itself is not directly coupled with the rate G at which the face advances parallel to itself. The spiral step mechanism of Frank (1949) was invoked as being the simplest mechanism which allows a natural physical relation between G, f and v. Then, if the steps gather adsorbed molecules from within a limited distance from the step, all of the growth parameters may be qualita- tively explained. This catchment distance is usually taken to be the mean migration distance on the surface, xs (Mason et ai, 1963). It is the purpose of this paper to reconsider this basic parameter and at the same time develop a total picture of the growth process, both qualitatively and quantitatively. 2. Previous attempts to understand x, Previous attempts to explain the measured tempera- ture dependence of the step velocity v and the mean migration distance xs have not been wholly successful. The crucial parameter xs is a function of the mean time t that a typical molecule resides in the adsorbed state: x? = D,t, (5) where Ds = DQt\p(-L','kT) (6) is the surface diffusion coefficient and U the activation energy. The residence time r9exp(W/kT) (7) is the inverse of the desorption constant used by Hobbs and Scott (1965), where II' is the energy of attachment to the surface. However, II' is expected to be greater 1293 ;w. J Ol'RN A I- A T HE A T MOSI'M E R I C S C I E N C You mi M o to - 6 o< o l\ \ \ \ \ -30 -20 TEMPERATURE 10 (°C) Fig. 2. Comparison of different theoretical growth parameters with the experimental data of Hallelt (1961). than [' so that the calculated values of .v., decrease with increasing temperature, with the trend shown by the dashed line in Fig. 2. If step velocity v is propor- tional to x„ such a trend clearly contradicts the experi- mental results of Hallett, shown as the solid curve. To counter this tendency and force xs to have the more desirable upward trend with temperature, Mason el al., suggested that the values of U and II" in Eqs. (6) and (7) are each strong functions of temperature and, moreover, contain a discontinuity at the appropriate temperature which generates the maximum and minimum. To provide a more plausible explanation, Hobbs and Scott considered the possibility that molecules already on the surface hinder the subsequent adsorption of other molecules, giving rise to a so-called "blanketing" effect. This had the effect of defining a new step collec- tion distance with a slightly improved temperature de- pendence (note the trend in the dotted velocity curve in Fig. 2). However, at the low supersaturations usually used it can be shown that the "blanketing" effect is insignificant. Thus, this approach, too, is unable to explain the strange temperature trends to .v, oi v in a satisfactory manner. In a simplified way, the trends with temperature of all of the growth variables (linear growth rates, step velocity, and migration distance) may be thought of as a superposition of a strong average trend upward with increasing temperature together with a nearly discon- tinuous change between each maximum and associated minimum. As suggested by several authors (Mason (7 al., 1963; Ryan and Macklin, 1969) it is very likely that two independent phenomena are responsible for the net effect. The discontinuity, the origin of the maximum and minimum, is often considered to be an effect of a surface reorientation or Faraday's so-called "quasi-liquid" layer (Weyl, 1951; Fletcher, 1962, 1968). Most studies of the behavior of steps on ice, however, have been concerned with the average upward trend and this is also a prime purpese of the present work. 3. The effects of multi-layer adsorption a. The adsorption model Previous treatments of the adsorption of molecules onto the surface of ice have considered only monolayer or Langmuir adsorption, with a single adsorbate-solid interaction (Hobbs and Scott, 1965). It is this simple adsorbate-solid interaction, via Eq. (7), which most likelv results in an unacceptable trend in r and in xs with temperature. It is, however, readily accepted that in many adsorption systems the interactions between the adsorbed molecules themselves can virtually domi- nate the interactions with the underlying solid and lead to very large effective residence times. This occurs in multi-layer adsorption especially at pressures ap- proaching the liquid condensation pressure. Of course, when liquid begins to form on the surface the number (if adsorbed molecules and the residence time increase virtually without bound. Since water vapor adsorbs in multi-lavers in some systems (Gregg, 1942), it seems 1294 M wu-ii 1(>7I I) I' \ \ I S I.AMI! \NH U I I I I \ M l> ^ ( O 57.? reasonable to expect such adsorption on its own solid, ice. In addition, it i^ very interesting that as the tem- perature of a crystal approaches its niching point, the pressure of vapor in equilibrium with the solid steadih and natural!} approaches that in equilibrium with the supercooled liquid. This means that, if multi-layer adsorption of water vapor can incur on ice at all, new possibilities arise for helping us understand the growth characteristics of ice cyrstals. In order to develop this picture more quantitatively, consider the model of multi-layer adsorption developed b\ /Jrunauer, /.mmett and Tellei (lu.vS). In utilizing this BET theon we realize that it has many failings but, nonetheless, it does describe a number of adsorption systems quite well. In any case, the intent of the follow- ing treatment is to present a quantitative example of multi-layer adsorption which fits our physical picture. The effects we are trying to illustrate would arise from anv model in which the concentration >i [cm-2] of adsorbed molecules increases with increasing pressure sufficiently strongly near the liquid condensation pressure. The approach to the liquid condensation pressure is usually specified by the relative pressure, P X= , (8) Pl(T) where P is the vapor pressure in dynamic equilibrium 0 0 5 10 RELATIVE PRESSURE X=P/PL Fig. 3. Adsorption isotherms for various values of the adsorption parameter C, according to the model of Brunauer el at. (1938). -30 -25 -20 -15 -10 TEMPERATURE CO Ik.. 4. The composite dependence of surface coverage n n,„ on temperature for different values of A /: = A i — /. /. . with the adsorbed layer and P l{T) a reference pressure which is usually considered to be in equilibrium with the supercooled liquid state. Generally, when the solid is growing, P = PS(T)+8P, (9) where Ps(T) is the equilibrium vapor pressure of the solid and 5/' the experimentally determined excess pressure. The relative pressure .V is thus a well-defined, monotonic function of temperature and, for small supersaturations, approaches unity as the melting point of the solid is approached. In the BET model the total surface concentration of adsorbed molecules is given bv nmCX (1-.Y)[1 + (C-1).V] (10) where n,„ is the number of adsorption sites on the solid [cm"-], and C=C(r)=C0exp[(£,-EL)/*r] sC0exp(A£/*r) (11) is an adsorption parameter which characterizes the system. In (11) Ei is the energy binding the fiist adlaver'2 to the solid, and El the binding energy between all subsequent layers. The form of Eq. (10) is shown in Fig. 3, in which typical adsorption isotherms for various values of C are depicted. Generally, E\> El, 2 The prefix "ad" is used to imply involvement in the physical process of adsorption in an abbreviated way. Thus, "adlaver" is a layer of molecules adsorbed onto a surface and may be inter- changed with "adsorbed molecular layer." Similarly, "admolecule" (used later) is an adsorbed molecule. 1295 574 JOURNAL OF THE ATMOSPHERIC SCIENCES Volume 31 - 1 C0 50 1 i : 1 : 1 : 1 { l | l Co = 10"* l U ■ 6 0 kcol/Mole EH -- 12 8 kcol/Mole E,2= 110 kcol/Mole I I 1 T, ■ -5°C l 1 - l l i - / 1 • 1 1 / / i/ i / / • • • / i i i f / / / z " - i / - __ - rr^"^ i / __l i i i i ' ' i i i 1 .1 ' i i 10 9 - 8 3. 7 >< Ixl o 6 < - 5 - 4 3 2 H 1 -15 -10 TEMPERATURE Fig. 5. The mean migration distance .r5 as a function of tem- perature, calculated from Eq. (18) and normalized to a common value at — IOC by adjustment of Do. so that C introduces a decreasing temperature de- pendence to n in Eq. (10). This temperature dependence will, however, be strongly countered by the tendency for X(T) to approach unit}' and therefore for the surface coverage to increase to many layers as P approaches Pl(T). It is this second effect, arising from strong adsorbate-adsorbate interactions, which may be re- sponsible for the tendency of all of the growth variables to increase with temperature. If for now we assume Co=l, then for various values of A£=£j — El the dependence of n/nm on temperature may be plotted as in Fig. 4. Even when the negative temperature coeffi- cient introduced by C(T) is strong, its effect on 11 is always dominated near the melting point by the approach of X to unity. b. TI:c residence time r In order to estimate the length of time that vapor molecules reside in the adsorbed layer, consider the equilibrium state and small deviations from it. At equilibrium, the desorption flux leaving the adlayer must just balance the adsorption flux entering the layer to maintain a given surface concentration. Now let the partial pressure of water vapor exceed the equilibrium value by an amount hP so as to increase the flux of mole-, cules entering the layer by (35F, where /3 is a sticking or adsorption coefficient to account for impinging mole- cules which are simply reflected. Since each of the additional vapor molecules which enters the adsorbed layer will, on the average, reside in the adsorbed state for a time r before it desorbs, the surface con- centration will increase by an amount 8n = r(3bF. So, t may be calculated from the isotherm [Eq. (10)] using Sn 1 5n to give (38F i3kr 8F k,„C[1 + (C-1).Y-] (3kTpL(i-xy-[i+(c-i)xy' (12) (13) Particularly interesting is the term (1 — A') in the denominator. In Eq. (13) [as in Eq. (10)] this term approaches zero as the temperature approaches the melting point. This means that, near that point, the residence time and the number of adsorbed molecules increase greatly. To compare Eq. (13) with the expression fot r used by others, note that if A' is small, nmC likTPL{T) \3kTP »mC0 exp(£, 'kT) (14) when the vapor pressure is written in the approximate exponential form, Pl = Plo exp( — EL/kT). Thus, for low surface coverages the temperature dependence of r is determined primarily by the energy E\ binding the first layer to the substrate and t has essentially th^ temperature dependence expected from the classical theory [Eq. (")]. Since .Y is small at low temperatures, r will have the classical downward trend with in- creasing temperature until X attains an appreciable value, at which point the trend will be reversed. These results suggest that it may have been the assumed limitations to low surface coverage and no lateral interactions which have previously hindered the de- velopment of a more complete picture of the growth process. It must be realized, however, that although the adsorbate-adsorbate interactions are responsible for the generally increasing residence times as the temperature approaches the melting point, the vapor molecules are adsorbed at all only by virtue of interactions with the underlying crystal. Hence, it is reasonable that the adsorption should be sensitive to the energy which bonds the first molecular layer to the solid even in the warmer region where adsorbate interactions dominate. The bonding directly to the solid might become weaker, for instance, if, indeed, a transition or reorientation of the molecules in the surface occurred. In this case, the number ;; and average residence time r of the adsorbed molecules would be expected to be reduced rather abruptly. On either side of the transition temperature the average trend upward would still be preserved, 1296 March 1974 I) K N N I S 1. A M B A N I) WILLIAM I) . SCOTT 3/0 n_ n(x) ne / * ,, *s 1"*- x = 0 — *\x%> ^ .c Jir/tr/t/j/f/jt//? , Fig. 6. The cross-sectional geometry of two parallel steps. but a discontinuity in the growth parameters would be expected, perhaps giving rise to the observed maxima and minima. To treat this idea quantitatively, allow the adsorbate- solid bonding energy E\ to take on different values above and below the transition. Thus, below the transi- tion temperature T,, C(rr()=Coexp[(£i.,-£z.)/*r]. (16) (17) The actual temperature at which the solid surface transition should take place is, of course, a function of the surface energy of the particular face, so the maxima and minima introduced into any growth parameter would be shifted relative to one another on the basal and prism faces. c. The mean migration distance xs Having now obtained an expression for the mean residence time and some insight into the possible origin of the quasi-discontinuity, we may use Eq. (5) to arrive at the final expression for the mean migration distance on the adsorbed multi-layer: nmDsCPL[PL-+(C-l)Ps-l x;-(T) = . (18) j8*r(Pi-P.)*[i,i+(C-l)P.]J The magnitude of xs(T) has been plotted in Fig. 5 for various values of Co, the pre-exponential factor of the adsorption parameter C(T), and using the two values of Ei specified by Eqs. (16) and (17). As indicated, both the trends of the curve and the magnitude of the discontinuity are portrayed realistically by the theo- retical curves at least for small values of C0. It is not expected, however, that the shift in the value of E\ would, in reality, occur as abruptly as has been as- sumed in the model, but to treat £i in any other manner would presently be unjustified. 4. Surface steps and the growth of ice a. Step velocity In the last section the functional form of the mean migration distance xs was derived without regard to the existence or behavior of steps on the surface. Here xs will be used as an input parameter to treat the interac- tions of steps with one another and to determine their contribution to the linear growth rate of a face. As was done by Hobbs and Scott (1965) let us con- sider the mass balance of adsorbed and migrating mole- cules on the surface, but with two differences: 1) there exists, in general, a finite (sometimes large) equilibrium concentration ne of adsorbed molecules which serve no growth function, and 2) two parallel neighboring steps are allowed to interact by competing for the available excess of adsorbed molecules. The geometry for this development is that used by Strickland-Constable (1968) and is shown in Fig. 6. The x coordinate is taken perpendicular to the steps with the origin one- half the distance x0 between them. The concentration of excess admolecules dn is determined as a function of surface position x from the equation of molecular continuity, i.e., from d-(Sn) Ds KD5n+(38F = Q, dx- (19) which simply accounts for the molecular fluxes due, respectively, to surface migration, desorption and ad- sorption. The assumption that the desorption flux is linearly proportional to the excess concentration Sn is justified whenever the deviation from equilibrium is small. The proportionality constant Kd is the desorp- 1297 576 JOURNAL OF THE ATMOSPHERIC SCIENCES Volume 31 a. EQUILIBRIUM b. GROWTH Fig. 7. The generation and growth of a step in a face by the emergence of a screw dislocation. tion probability per unit time, the equivalent of the desorption constant used by Hobbs and Scott; it is the reciprocal of the residence time t. Thus, from Eq. (5), KD = 1/V = Ds/xs-, and the solu- tion to Eq. (19) is tcosh(.v/.vs) " 1 , (20) cosh(.v0/2.vs)J which assumes that the outer boundaries are growing steps which act as infinitely good sinks for excess ad- molecules, i.e., 5«(±x0/2)=0. Molecules diffuse to each step of height h, enter the step, and provide for its advance at a rate v given by »« (2Q/h)xap8F tanh(.r0/2.vs), (21) an expression which cares for the case of a limited fetch. Note that this expression degenerates to the simplified equation given by Hallett (1961) and by Hobbs and Scott when .rs<$Cxo. In general, however, each step will have neighboring steps which compete for the supply of adsorbed molecules so that the full expression [Eq. (21)] is necessary. b. Step sources The development leading to Eq. (21) gives an idea of how steps interact on a surface characterized by. the parameter .v,, provided that the steps exist in the first place. Remember that, without a continual source of steps somewhere on the surface, steps will simply advance to the crystal edge and disappear, stopping further growth. This means that, since regeneration of steps by two-dimensional nucleation, with ensuent growth, is energetically improbable at the low super- saturations normally present during growth, a mecha- nism other than two-dimensional nucleation must be responsible for the growth which is observed (Cabrera and Burton, 1949). The most likely mechanism is that first proposed by Frank (1949) and based upon the emergence of screw dislocations at the surface. This spiral step mechanism does seem to be the dominating mechanism of growth with some other substances (Bradley and Drury, 1959) ; also, observations have been made of spirals on crystalline faces of ice growing from the melt (Ketcham and Hobbs, 1968) and of curved trains of steps during vapor growth (Lamb and Scott, 1972). As seen schematically in Fig. 7a, when one part of the lattice is shifted relative to the other by a shearing action, a step will necessarily appear in the surface and have the important characteristic that it can never disappear as long as the screw dislocation con- tinues to emerge on that face. Under conditions of equilibrium the step will be stationary and straight. In the presence of a supersaturated vapor, however, the step will advance and wrap itself up into a spiral about the dislocation, as seen in Fig. 7b. Following the treatment of Burton et al. (1951), we assume that the spiral has a stationary geometry which is approximately Archimedean such that the radius vector r from the dislocation is proportional to the angular distance 0 by r{6) = Kd, (22) where k is a temperature-dependent proportionality constant. The spacing .v0 between steps is then Xo=27TK, (23) and the velocity v of steps far from the center of the spiral is v = (2Sl/k)x£5F tanh (»«/*.). (24) 1298 March 1974 DENNIS LAMB AND WILLIAM D . SCOTT 577 c. The linear growth rate Obviously, for each full rotation of the spiral another step will be released from the center and allowed to propagate across the crystal face. The frequency / with which such steps are "generated" is the minimum radius of curvature (at 0 = 0) so that v Zttk (25) For a spiral step of height h, a new layer of crystalline material of thickness /; is added to the growing face every time a step passes. Thus, the rate G at which a face advances parallel to itself is given by or, using Eq. (25), G=fh, vh G= — . 2-7TK (26) (27) The final dependence of the growth rate on the surface parameter xs and the step shape factor k is therefore G=fl/35F(.vs/V(c) tanh(7r/c/.vs). (28) Of particular interest is the fact that this does not depend on the specific value of the step height or, therefore, on the magnitude of the deplacement vector of the screw dislocation. The linear growth rate depends only upon the simple existence of a dis- location emerging at the surface with a screw component and upon the adsorption behavior of the water mole- cules. Also, although this treatment has been limited to a single step source, it is nevertheless general since it can be shown that the linear growth rate is governed solely by the single most active source on a face ; the contribu- tions to the growth from other, independent step sources is not additive (Strickland-Constable, 1968, p. 200). It is for this reason that a crystal face which is large compared to the mean migration distance may still maintain its relatively flat form even while growing in the presence of strong lateral gradients of excess pressure. Growth is strictly governed by the frequency at which steps pass a given point, this frequency being determined by conditions at the center of the most active spiral. d. The critical embryo To complete this treatment, the temperature de- pendence of. the spiral shape factor k is required. This dependence is necessarily speculative since little is known about the actual behavior of steps in the im- mediate vicinity of the emerging dislocation core. Nevertheless following the treatment of Burton et al., we assume that the radius of curvature of the step can never be smaller than p*, the radius of a critical two-dimensional embryo. This critical radius occurs at ■2P*. (29) If it is now assumed that molecular incorporation occurs at the steps by exchange with the adsorbed layer only, the temperature dependence of p* can be found. First, consider a step without curvature. The molecular exchange which occurs between the step and the adsorbed state may be thought of as being com- prised of a flux /, of molecules continually entering the lattice at the step (and contributing to its advancement) and a flux f0 of molecules leaving the step (tending to retard the advancement). To a first approximation, the flux into the step is proportional to the concentration of molecules ;?o directly in contact with the step: fi—biito, (30) where b, is the proportionality factor. The flux leaving the solid surface at the step, on the other hand, is inde- pendent of Ho but is expected to be dependent on the temperature and the energy £0 required to remove a molecule from the lattice and place it in the adsorbed state. This is commonly expressed through the standard Arrhenius form fo = A exp(-E0/kT), (31) where A is a configurational term and E0 the energy required to create the intermediate, activated state. At equilibrium, the incoming flux is just balanced by that outgoing, i.e., fi—bine = fo=A e-xp(—Eo/kT), (32) which implies n.= (A/bi)txp(-Eo/kT). (33) For any concentration greater than this equilibrium value the step will advance and wind up into a spiral having radii of curvature which continually decrease toward the center, the site of the emerging dislocation. But, because of the finite curvature, the activation energy at any point along the spiral, where the radius of curvature is p and the edge energy is rj, will be reduced to rja Ea = Eq , P (34) where a is the lattice spacing (see Burton et al.). Now, if a quasi-equilibrium is maintained, the concentration nc of adsorbed molecules in close proximity to the curved step is, from Eq. {33), nc=(A/bd exp{[E0-Ua/p)]/*n, (35) or nc = nc exp(r)a/pkT). (36) The exact center of the spiral does not grow because the high curvature prevents any net flux of molecules 1299 578 JOURNAL OF THE ATMOSPHERIC SCIENCES Volume 31 I 1 /"- \ : / \ : / / \ / /" l\ : ,/ /^"""H \ i " / Co = 10" U \ " ■ '' r; - 2«I0"" ergs/mol *\ \ . En= 12 8kcol/Mole >\\ - E12= II Okcal/Mole \\\' T,=-5°C \l written 3^ a < < -30 -20 -10 TEMPERATURE (°C) Fig. 8. The dependence of the critical radius p* of a two- dimensional "pillbox" imbedded in an adsorbed multi-layer (for 5P=10iJ.m Hg or 13.3 jtb and the same normalization as Fig. 5). from entering into the lattice. Hence, near that point there is no accumulation and, specifically, no diffusive term in Eq. (19). The concentration of adsorbed mole- cules near the spiral center should then just equal that concentration (««,) that would exist far from any steps : where Hence, and or ««, = ««+ Ah, 08F A« = - KD nc = iie exp(iia/p*kT) = iu, rjd (37) kT In (»«/»„) ■qa we kT An (38) (39) for small departures from equilibrium. Through the BET equations, ne and An are functions of the satura1 tion and excess pressures, so Eq. (39) can also be va \(Pl-P.)LPl + {C-1)P.])P. kT\ Pl2+(C-1)P/ SP (40) which, when C= 1, reduces to the simpler expression i,a /PL-P.\P, Va /Pl-PAP, kT\ PL )bP (41) Eqs. (40) and (41) predict an extraordinary tempera- ture dependence for p* (see Fig. 8). At the lower tem- peratures (below about — 12C) when PL — PS is in- creasing or constant with increasing temperature, p* increases with increasing temperature in a manner pre- dicted by classical theory. However, at the warm tem- peratures near OC, when Pl—Ps approaches zero, p* decreases with increasing temperature. The effect is directly related to the number of adsorbed layers on the surface: when there are few adsorbed molecules, there is classical behavior; but, when many are present, nucleation effects are reversed. [It is interesting that Ownby (1972) and Sandejas and Hudson (1968) have found multi-layer adsorption during adsorption on metals, and at the same time, a marked decrease in the observed values of the critical supersaturation.J e. The condensation coefficient and the primary habits The general expression for G given in Eq. (28) may now be compared with G,nax to obtain a value for the condensation coefficient a, which, as defined earlier, is the probability of molecular incorporation. Eqs. (1) and (2) predict that G=ai25F, (42) which, when compared with Eq. (28), indicates that a=/?[(.v.,/™) tanh(™/.vs)], (43) or where a = 07, (44) 7= (xs/itk) tanh(irx/xs) 1 1 1 C0 = IO-« U ■ 6 0kcol/Mole E||= 12 8kcal/Mole 1 It - E|2= 110 kcal/Mole P •I T, = -5°C 1 i - /I /I 1 1 /•■ jl ■I 1:1 III - / 1 / ) / /I 1 jl jl 1 •' - --'A ' ■■■' i / / '' - : 1 •'/ / - r i i 1 i i i I 1 i i 10 -8)- rS 6£ 5 o < rr 4 2 • (T-) k «(L-*) *p « (M2L-6T-') g/t ,«(M-1L4T-2) Using the above relations the results for the inertial subrange are E^e^ur2, (15) , t2/3£-5/3# (16) For the buoyancy subrange in a stably stratified fluid, the results of the dimensional analysis are (17) r^-XpW-2 r*«x„4/5(g/po)-2/6£-7/5 E^xp(g/Puy^ £*-x,2/5(g/po)4/6£-11/6. (18) (19) (20) Eqs. (18) and (20) are identical to Bolgiano's (1959) equations (11) and (12), while Eq. (16) agrees with Kraus's (1972) equation (1.83). In the case of a stably stratified fluid, X„, the rate of production of mean square density fluctuations, is an important parameter because the same fluid motions that convert kinetic energy to potential energy by working against the buoyancy forces also generate deviations of potential density from the mean distribution. These potential density fluctua- tions eventually are broken up and finally dissipated by viscosity. These potential density deviations are a measure of the eddy dissipation rate due to the mass field in the ultimate microscale through the term Kg[y (5p)D2/LPo(dp/dz)], where k is the conductivity, as shown by Long (1970) and also by Stern (1968). c. Turbulence theory for unstable stratified fluid At night the prime heating source, solar radiation, is removed and there is ongoing heat loss at the sea surface due to radiational cooling and sensible and latent heat fluxes. In the absence of precipitation and advection, the evaporation increases salinity, and total heat loss decreases the sea surface temperature. Both these processes increase the density of the surface water. Therefore, an unstable stratification becomes established soon after sunset and vertical overturning and convection become the main processes for redis- tributing the thermodynamic quantities at night. The net cooling at the sea surface can be seen in Fig. 4 as the dip in the sea surface temperature curve before the beginning of each heating cycle. Also, the mean vertical temperature differences between 10 and 20 m show negative values (see Table 3). The destabilization and resulting convective over- turning due to nocturnal cooling cause the increased energy levels at the higher frequencies during the 1310 October 1974 FEODOR OSTAPOFF AND SYLVIA WORT HEM 609 night periods. The slope of the daytime spectra is approximately —2 indicating isotropic turbulence, but the nighttime spectra show approximately a —1 slope. The change in slope is an indication that the frequency range of interest is dominated by either the viscous- convective subrange (Gibson and Schwartz, 1963) with a Prandtl number of the order of 10 or the buoy- ancy subrange (the part of the equilibrium range that reflects the anisotropy induced by the density gradient) for an unstably stratified fluid. The possibility of seeing the viscous convective sub- range in the frequency range of interest is considered first. The transition between the inertial subrange and the viscous convective subrange occurs in the vicinity of (e/V*Y> (21) in wavenumber space. Equivalently, in frequency space it is «d=(f/")!, (22) where v is the kinematic viscosity. The kinematic viscosity does not change significantly, and can be regarded as a constant. For an unstably stratified fluid, potential energy is available in the mass field which can be readily converted to kinetic energy. Therefore, for steady-state conditions, the viscous dissipation t is larger than the rate of input of mechanical energy because of the conversion of the available potential energy of the mass field to turbulent kinetic energy. Then viscous dissipation is increased at night for similar turbulent energy input, and the viscous convective sub- range tends to move to higher wavenumbers and fre- quencies. If the observed —1 slope for the nighttime spectra were due to the presence of the viscous-convec- tive subrange occurring in the frequency range of interest, then ud must decrease from day to night. Therefore, the — 1 slope cannot be explained by the viscous-convective subrange and therefore must occur in the buoyancy subrange, which is on the small- wavenumber and low-frequency side of the inertial sub- range. The buoyancy subrange for an unstable stratified fluid is considered next. For unstable stratification, the density (or temperature) is not a passive contaminant. It is an active contaminant because it contributes to the generation of velocity fluctuations (Tennekes and Lumley, 1972). A consideration of the available poten- tial energy provides some insight into the selection of suitable parameters for describing the energy density, and density anomaly spectra. The available potential energy can be written as (Kraus, 1972) 1 f APE=— J p'gzdxdydz, V J R (23) and the density field is defined by p(x,y,z,t) =p0+p'(z)+p"(x,y,z,l). (24) Here p0 is the overall density average, (po+p') is a density distribution that could be derived in a stably stratified fluid from an arbitrary existing state by making all equal density surfaces horizontal without any change of mass between them (the density in a fluid in hydrostatic equilibrium), and p" is the non- hydrostatic contribution (Kraus, 1972). Integration by parts of the integral in (23) gives an alternate expression for the APE*: V A z2~\ 1 f z2 APE=\—pg-\ -- -gdpdxdy. (25) IV 2-U, VJR2 Therefore, changes in the value of the APE are repre- sented by changes in either the integral in (23) or the integral in (25). Eq. (23) represents the APE as seen by the momentum field or velocity fluctuations. It appears that the parameters p'g and z, perhaps in the form dp/dz, are important to the velocity fluctuations. Therefore, the parameters (g8p) and (dp/dz) have been selected for use in the dimensional analysis of the energy density field. The results are as follows: E„~{gbP){dp/dz)-^-\ Ek~(g6p)(dp/dz)-lk-K (26) (27) The integral in (25) represents the APE as seen by the mass field. From this integral, it appears that g' [the reduced gravity {gdp/pa)~\ and z2 [perhaps in the form (5p)2 since dz={dz/dp)dp~\ might be selected as the parameters important to the rearrangement of the mass field. Using these parameters, the resulting mass field spectral densities are rM«(8P)v-s lW5p)2£-'. (28) (29) where V is the volume of the region of integration R, The parameter g' drops out of the expressions. From these arguments, a —1 decay law appears in the buoyancy subrange for an unstably stratified fluid. Previous work which considers spectra in an un- stable stratified fluid is that of Monin (1962). He takes a limit for very small wavenumber in the inertial subrange and determines that both Ek and T, approach constant values. The authors believe that this offers a further indication that slopes for these quantities in the buoyancy subrange should be expected to be less negative (i.e., —1 as opposed to —2 or —5/3) for an unstable stratified fluid than the slope in the main part of the inertial subrange. The limit of very small wavenumber taken by Monin is seen as the small wavenumber limit of the buoyancy subrange considered above. Therefore, the buoyancy subrange is considered 4 The first term on the right-hand side of (25) is evaluated around the boundary of R. 1311 610 JOURNAL OF PHYSICAL OCEANOGRAPHY SCALAR QUANTITY SPECTRA Volume 4 log(rj DAY (STABLE) log (rj buoyancy subrange inertia! subrange T NIGHT (UNSTABLE) buoyancy subrange inertial subrange Driving ND ND /*d\'/2 - w "mm umox |_il| Frequency I v I 1 1 Driving Nw . Frequency Nk »r log (FREQUENCY) log (F.1EQUE ?*CY) Fig. 9. Scalar quantity spectra for stable and unstable conditions. to be between Monin's low wavenumber limit and the usual inertial subrange. For the case in which salinity is essentially constant, temperature fluctuations represent density fluctuations. This occurs in the data set used to calculate the spectra in Figs. 5 through 8. It is of interest to consider over what frequency range the buoyancy subrange might be expected. Tennekes and Lumley (1972) define a buoyancy time scale tb for the case of unstable stratification. For the oceanic case it can be defined as (Tennekes and Lumley use potential temperature ) subrange is expected to be g d'P\ po dz\ One can then define a buoyancy frequency scale o3h = tb~1. (30) (3D It is to be expected that the buoyancy subrange should appear in the vicinity of u>b, since wi is defined in terms of the mean stratification. The frequency separating the buoyancy subrange on the high-frequency side and the inertial subrange on the low-frequency side is expected to be the maximum local buoyancy frequency scale of the mean density profile, i.e., U>b max — L-PO dpi 1» U£ i max-1 (32) w& LPol 021 minJ A buoyancy period can be defined as Pb= 2irtb. Hi) (34) Similarly, the low-frequency extent of the buoyancy This is the same numerically as the Brunt-Vaisala period for a stably stratified fluid. Figs. 9 and 10 show how the scalar quantity spectra and energy spectra are expected to appear according to the theories presented in Sections 5b and 5c. 6. Buoyancy time and space scales For the six 8-hr segments of the low-passed 10, 20, 30 and 40 m quartz thermometer records, mean tem- perature values for each segment have been calculated. Using the temperatures instead of densities (the salinity did not change within the STD resolution), calculations of the buoyancy time scale and the Brunt- Vaisala period (where applicable) have been made according to Eq. (34). The results are shown in Table 4. The striking result is that where the stratification is unstable, i.e., between 10 and 20 m during the night- time segments, the buoyancy period is nearly the constant value of ~24 min. Since the temperature gradient can be calculated only to a depth scale of 10 m, this represents a bulk buoyancy period and not a local maximum or minimum. Therefore, the buoyancy subrange would be expected to appear in this frequency 1312 October 1974 FEODOR OSTAPOFF AND SYLVIA W O R T H E M ENERGY SPECTRA DAY (STABLE) NIGHT (UNSTABLE) 611 log (E( log (EJ subrange buoyancy\— 2 subrange T 1 1 r- Driving N0 ND llO\,/7 Frequency °m,B °"« l~ ) log (FREQUENCY) buoyancy subrange inertial subrange Driving NN Frequency 'Nmo. (!H1,/J log (FREQUENCY) Fig. 10. Energy spectra for stable and unstable conditions. range for the unstable stratification occurring during the night periods. Since the spectra in frequency space for the inertial subrange are expected to decay as u-2 [Eq. (15)] and ru is also expected to decay as w~2 for a stably stratified fluid [Eq. (17)], a Tu spectrum would not illuminate the question of the stably stratified buoyancy subrange. However, the data appear to be consistent with the above theory. It should be remem- bered that the 40 m record contains some intrusion of the pycnocline due to the internal tide and that the diurnal heat wave is barely observable in the 30 m record. In order to derive the buoyancy space scale, it is necessary to estimate the mean speed of the water past the sensors. As mentioned above the sensors were suspended under a parachute drogue buoy. In order to keep the parachute open some slippage must occur and this has been estimated to be 3.0-3.5 cm sec-1. This is a mean speed derived from the mean buoy drift as de- termined by hourly bearings from the ship and absolute ship positioning by excellent satellite fixes as well as the passage of a salinity front through the experimental Table 4. Buoyancy time scale calculations. Segment Day or PlO-20 m P 20-30 m P 30-40 m no. night (min) (min) (min) 1 D 8.35 16.18 8.40 2 N 25.48* 41.08 5.96 3 D 6.96 15.81 17.36 4 N 24.55* 183.7 13.97 5 D 13.62 15.81 20.80 6 N 23.52* 42.15 20.04 * Unstable conditions. area which was taken as the mean advection of the water mass. This salinity front moved through the experimental area about 2 hr after the data presented above were obtained. It is used here merely to estimate the mean drift. With a value of 3.0-3.5 cm sec-1 and a time scale of 24 min, the buoyancy space scale is estimated to be about 40-50 m which was the order of the mixed layer depth in the experimental area. Acknowledgments. Fortions of this work were sup- ported by the National Science Foundation under IDOE Grant AG-282, which is gratefully acknowledged. The quartz thermometer system was designed and constructed by D. Waters of AOML who also super- vised the field operation of the system. We also ac- knowledge with great pleasure the extremely fine cooperation of the Commanding Officer of the Dis- coverer, Capt. R. Munson, and the Operations Officer, Cdr. R. Allbritton, without whose skill and enthusiasm this difficult field work could not have been accom- plished. The buoy work was expertly handled by the Chief Bo'sun, Mr. William Guthrie. Lt. T. Ruszala diligently worked up the navigational data, which we gratefully acknowledge. REFERENCES Batchelor, G. K., 1953 : The Theory of Homogeneous Turbulence. Cambridge University Press, 197 pp. Bolgiano, Jr., R., 1959: Turbulent spectra in a stable stratified atmosphere. J. Geophys. Res., 64, 2226-2229. , 1962 : Structure of turbulence in stratified media. /. Geophys. Res., 67, 3015-3023. 1313 612 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 4 Bowden, K. F., M. R. Howe and R. I. Tait, 1970: A study of the heat budget over a seven-day period at an oceanic station. Deep Sea Res., 17, 401-411. Fedorov, K. N., 1972: On the summer daily heating and diurnal heat budget of the upper ocean layer. Studies in Honor of G. Aliverti, Inst. Meteor. Oceanogr., University Navale di Napoli, 27^0. Gibson, C. H., and W. H. Schwartz, 1963: The universal equi- librium spectra of turbulent velocity and scalar fields. J. Fluid Mech., 16, 365-384. Hasse, L., 1971: The sea surface temperature deviation and the heat flow at the sea-air interface. Boundary Layer Meteor., 1, 368-379. Hoeber, H., 1972: Eddy thermal conductivity in the upper 12 m of the tropical Atlantic. /. Phys. Oceanogr., 2, 303-304. Howe, M. R., and R. I. Tait, 1969: Some observations of the diurnal heat wave in the ocean. Limnol. Oceanogr., 14, 16-22. Kraus, E. B., 1972: Atmosphere-Ocean Interaction. London, Oxford University Press, 275 pp. Leetma, A., and C. S. Welch, 1972: A note on diurnal changes in momentum transfer in the surface layers of the ocean. /. Phys. Oceanogr., 2, 302, 303. Long, R. R., 1970: A theory of turbulence in stratified fluids. /. Fluid Mech., 42, 349-365. Monin, A. S., 1962: On the turbulence spectrum in a thermally stratified atmosphere. Izv. Akad. Nauk SSSR, Ser. Geofiz., No. 3, 266-271. Naval Air Systems Command, 1967: Handbook Operation, Service and Overhaul Instructions with Illustrated Parts Breakdown Meteorological Station, Automatic, Marine AN /SMT-1. NAV- AIR 50-30 SMTI-2, 200 pp. Ostapoff, F., Y. Tarbeyev and S. Worthem, 1973: Heat flux and precipitation estimates from oceanographic observations. Science, 180, 960-962. Shonting, D. H., 1964: Some observations of short-term heat transfer through the surface layers of the ocean. Limnol. Oceanogr., 9, 576-588. Stern, M. E., 1968: T-S gradients on the microscale. Deep Sea Res., 15, 245-250. Stommel, H., and A. H. Woodcock, 1951 : Diurnal heating of the surface of the Gulf of Mexico in the spring of 1942. Trans. Anter. Geophys. Union, 32, 565-571. , K. Saunders, W. Simmons and J. Cooper, 1969 : Observa- tions of the diurnal thermocline. Deep Sea Res., 16, 269-284. Tennekes, H., and J. L. Lumley, 1972: A First Course in Turbu- lence. The MIT Press, 300 pp. Woods, J. D., 1968: An investigation of some physical processes associated with the vertical flow of heat through the upper ocean. Meteor. Mag., 97, 65-72. 1314 A REMOTE SENSING STUDY OF PACIFIC HURRICANE AVA D. ROSS National Oceanic and Atmospheric Administration Miami, Florida B. Au Naval Research Laboratory Washington, D. C. W. Brown Jet Propulsion Laboratory Pasadena, California J. McFadden National Oceanic and Atmospheric Administration Miami, Florida ABSTRACT Aircraft, SKYLAB, NOAA-2, ATS-3, and NIMBUS-5 recently obtained a variety of measurements of Pa- cific Hurricane AVA. These measurements are unusu- ally broad in scope and include satellite observed passive microwave emissivities at 13.9 + 19.5 GHz, active microwave scattering cross-sections at 13.9 GHz, and near infrared and visible images. Essen- tially simultaneous aircraft measurements of wind speed, waves, whitecaps, 1.4 and 13-15 GHz passive microwave emissivities, 1.4 GHz active microwave images, sea surface temperatures, pressure fields, and aerosol size distributions were also obtained. A brief description of sensors and platforms is presented along with some in-depth details of re- sults obtained. These results confirm the sensi- tivity of microwave emissivity to foam and liquid water in the atmosphere. Wave measurements from the aircraft show significant differences in the shape of the energy spectrum when compared to other fetch-limited spectra. Whereas fetch-limited spec- tra are sharply peaked, the hurricane spectra re- mote from the eye are broad, indicating the pre- sence of swell and increased energy transfer within the spectrum due possibly to non-linear interac- tions, while those near the eye are sharply peaked. The SKYLAB RADSCAT, operating at 13.9 GHz in a cross-track mode, obtained microwave measurements of a portion of the storm in both the active and the passive mode. Preliminary results show that the scattering cross-sections increase when viewing the hurricane despite an expected attenuation due to rain. Passive measurements increase as expected and are in general agreement with NIMBUS-5 measure- ments at 19.5 GHz. Aircraft measurements of microwave brightness temperatures at L band show an increase which is 163 1315 largely due to foam and whitecaps while those at X and KU band are contaminated by rain. Active co- herent L-band radar images of swell produced by the hurricane were obtained enroute to the storm. These images indicate a strong interaction takes place be- tween long and short gravity waves. Flight level wind speeds were obtained by means of an inertial navigation system and represent a sig- nificant increase in accuracy from past measurements of hurricane winds. Maximum winds encountered in the eye wall measured 137 knots, the highest ever for a Pacific hurricane, which had a record low cen- tral pressure of 914 mb. The use of extensive and coordinated satellite and aircraft measurements has provided an unprece- dented opportunity to study the dynamics of a hurri- cane. 1 . INTRODUCTION The development and application of remote sensing techniques to the study of man's environment has increased considerably in recent years. Perhaps the greatest return on monies invested in this area has been in use of satellites in observing and predicting weather. One aspect of weather phenomena which is currently being studied in great detail is tropical cyclones. A tropical cyclone is an intense vortex of high winds and large moisture concentrations which can have a devastating effect on man as they pass from water to land accompanied by high wind forces, in- ordinately high water (surge) levels, and large amounts of rain. Because cyclones are generally born in remote ocean areas, they have remained a' little understood phenomena. In recent years, however, aircraft have been used to study many aspects of the storms by means of a variety of in-situ measurements. More recently, satel- lites equipped with imaging systems have been of great utility in detecting the birth of cyclones and predicting the path they are most likely to follow during their lifetime. This paper describes a number of measurements of some unique aspects of a cy- clone obtained from aircraft and a variety of spacecraft and represents an unprece- dented opportunity to evaluate the capability of remote sensing instrumentation to contribute to the study of such phenomena. 2 . BACKGROUND The NASA SKYLAB experimental satellite was the catalyst needed to gel this ex- periment. Intended as a means of evaluating the Radar-Radiometer sensor packages aboard SKYLAB, an aircraft program was initiated to fly beneath the SKYLAB and mea- sure an extensive number of environmental parameters which might affect the signa- ture of the earth viewing satellite sensors. One of the aircraft involved was a National Oceanic and Atmospheric Administration (NOAA) C130 Hercules normally equipped to study hurricanes and other weather-oriented phenomena. For the SKYLAB program, a number of additional sensors were installed and are shown in Table I along with the parameter intended to be studied and expected accuracy. Figure 1 shows the NOAA aircraft with passive microwave radiometers extended out the rear cargo door. As the NOAA SKYLAB underflight program was getting underway, the first Pacific Hurricane of the season was forming and was named AVA, (Figure 2) . As one of the objectives of the SKYLAB program was to observe hurricanes, a data gathering pass was planned for 6 June 1973, using the SL 193 Radar-Radiometer in the solar inertial scanning mode. Unfortunately, a more extensive look at the hurricane with other SKYLAB sensors could not be arranged because of conflicting priorities. Indeed, the NASA system was literally turned upside down in order to schedule this limited pass. 164 1316 3. AIRCRAFT MEASUREMENTS The NOAA C130 deployed to Acapulco the morning of 6 June, refueled and com- menced its flight into the storm at 2107Z. Figure 3 shows the track of the air- craft along with isolines of flight level (500 ft.) winds measured with a Litton LTN-51 inertial system using the true airspeed output from a Kollsman differential pressure transducer. As a result of a measurement of an extraordinarily low cen- tral pressure of 915 mb obtained by an Air Force Reconnaissance aircraft approxi- mately three hours prior to our entry into the storm, it was decided a low level (500 ft.) penetration into the eye would be unwise. The portion of the track shown in Figure 3 from 2156 to 2315 was therefore flown at 10,000 feet. Low level (500 ft.) measurements of wind speed and direction, wave heights, whitecap densities, and microwave emissivities were obtained during the period 2107-2156, and again from 2325 to 2356. Microwave measurements, which require the cargo door to be open with extended radiometers, were not taken during the latter time period because of the reduced safety factor associated with high turbulence in conjunction with open cargo doors. Figure 4 is an example of laser altimeter profiles of waves in an area of 65 knot flight level winds. Figure 5c shows the spectra of this segment, mapped to fixed coordinates, along with a spectra of high waves measured in the North Sea (Ross, et al., 1970) . Also shown are spectra (Panel a, b) obtained at other regions within the storm plotted together with spectra of the same total energy obtained in the N-Sea and the North Atlantic. There are some significant differences between these sets of spectra. Those obtained near the eye (Fig. 5b, c) are sharply peaked and agree well with the N-Sea spectra which are severely fetch limited. The third spectrum was obtained approximately 110 nautical miles from the eye and shows con- siderably more low frequency energy than the North Atlantic spectrum which was es- sentially fully developed. In addition, this spectrum shows a reduced level of en- ergy on the high frequency side of the peak. We attribute this difference to non- linear interactions between the high frequencies and swell of frequencies near the peak which results in a broadening of the hurricane spectrum. Figure 6 shows the variation of wind speed and significant wave height with radial distance from the eye. The dashed line shows expected surface (20 meter) winds assuming a logarith- mic variation in wind between the surface and flight altitude (Cardone, 1969) . The significant wave height is known to vary as the square of the wind speed for fully developed seas. It can be seen in this figure that this relationship does not hold in a hurricane because of the fetch and duration limited character of the hurricane wind field. Observations of microwave brightness temperature were obtained during the per- iod 2107-2147. The data at the higher microwave frequencies are strongly affected by the presence of rain as one-minute average values at vertical incidence vary in- consistently from 130° to 145°, and 140° to 200° for X and KU Band respectively. Brightness temperature vs. incidence angle for this segment at L-Band is shown in Figure 7 along with data# for a low wind condition obtained 11 June. It can be seen that there is a systematic increase in brightness temperatures of about 4 K at all incidence angles. Inspection of simultaneous vertical photography reveals little thin foam streaking presumably because of the-»swell content of the seaway and the percentage of whitecap coverage is approximately 10 percent. Based on the results of Au, et al. (1974), presented elsewhere in this symposium, we attribute this in- crease to the whitecap (foam) coverage. Thus, a sensitivity of .4 K/% whitecap coverage is obtained. Enroute to the storm, coherent side-looking radar operating at a frequency of 1.35 GHz (A = 25 cm) was used to obtain surface imagery. A series of wave-like patterns is apparent in this imagery which appears to be a combination of locally generated wind waves mixed with swell coming from the hurricane. This imagery, to- gether with a vertical photograph obtained simultaneously, was digitized and sub- jected to two-dimensional Fourier analysis. Figure 8 shows the optical image of the two-dimensional Fourier transform at the top, along with a densitometer trace obtained along the axis of the principal direction (lower left, and center). Also shown is a composite hindcast wave spectrum constructed by using the wave spectra obtained at 2147Z along with a spectrum obtained in the Atlantic Ocean for a wind speed of approximately 22 knots. Surface winds at the time of this image were vis- ually estimated to be 20 knots, which was substantiated by sun glint analysis of ATS-3 Satellite imagery (Strong, 1973) . The position of the laser wave measure- ments and of the hurricane relative to the radar imagery is shown in the inset in 165 1317 the upper right corner of the figure. Good agreement between the wave lengths of the principal wave components can be seen. That the radar is imaging the waves is evident; not so evident is the scattering mechanism which allows detection of waves longer than the backscattering Bragg waves (Crombie, 1955). It has been demonstra- ted in several laboratory and field experiments (cf. Shemdin, et al., 1972, Mitsu- yasu (1971) ) that presence of a swell in a wind sea will reduce the amplitude of the wind-wave energy peak by an amount which is dependent upon the energy and fre- quency separation of the swell. Longuet-Higgins (1969) describes this interaction which results in shorter waves peaking near the crest of the longer wave as it pass- es by. The long waves thus modulate the Bragg waves which, in turn, modulate the return of the radar energy resulting in an image of the longer waves. Since more than one long wave component is seen in the image, it has been suggested (Stilwell, 1974) that this modulation is accomplished by interaction between all waves longer than the" Bragg waves. The radar imagery therefore may contain useful amplitude as well as wave length and direction information if the transfer function for the for- mer can be established. Unfortunately, the radar power supply gave out shortly af- ter this segment was completed so that no imagery of the local hurricane wave field was obtained during the eye penetration. 4. SATELLITE RESULTS Imagery and microwave data from a variety of satellites were obtained of the hurricane in various stages of development. A summary of these satellite studies is shown in Table II. Figure 9 is a composite of ATS imagery showing the track of SKYLAB as it passed near the storm. Unfortunately, the storm was moving rather fast, and although the SKYLAB antenna scanned to 52 incidence angle, only a small portion of data was obtained in the high wind periphery of the storm. This data, along with NIMBUS 19.5 GHz measurements of the same portion of the storm, are showr. in Figure 9 for the incidence angles of 45°to 52.5°. Also shown are rainfall rates inferred from the 19.5 GHz NIMBUS-5 radiometer (Wilheit, 1974). The purpose of the S 193 Radar-Radiometer is to infer surface wind fields from measurements of the microwave backscatter. The passive portion of the instrument is intended to provide a basis for correcting the return radar cross-section (a ) due to attentuation by liquid water. The inference of surface wind speed is furthe; complicated because the amplitude of the backscattered component is sensitive to the relative direction of the wind vector. Jones (1974) , from data obtained with an aircraft system at vertical polarization, reports a difference of about 5 db be- tween the upwind and cross-wind directions for a wind speed of 14 m/s and incidence angle of 40 , vertical polarization. The up-downwind asymmetry he observed of 1-2 db is further evidence of short wave modulation by longer waves. Estimates of wind direction along the footprint were made as previously described and resulted in positive corrections of 2-4 db. A backscattered component due to rainfall is not accounted for in the data which are summarized in Table III. It can be seen from panel a of Figure 10 that if a correction were applied to o values, due to rain attentuation, that the o° for both polarizations would in- crease with increasing wind speed between 1857:15 and 1858:00. Neglecting the val- ue at 1858:16, o° would then decrease at 1858:31, following the decreasing trend in surface wind. At the 45° incidence angle (panel b) , rainfall rates were markedly reduced and o° qualitatively agrees with trends in the wind speed. °ttv°' ^n ^ot^ cases, has been corrected for wind direction while no such correction has been ap- plied to a °. As with the coherent radar images, the o° is a measure of the ener- gy content of resonant Bragg waves - near capillary, or centimeter, wavelengths in the case of the S 193 radar. Phillips (1966) using dimensional arguments shows that the high frequency end (f^ > fm) * of the gravity wave spectrum should reach a maximum, or equilibrium, value. Increased energy transfer into this spectral re- gion would simply result in increased energy loss through wave breaking. Pierson and Stacy (1973) suggest three forms for the behavior of the high frequency end of the spectrum, including the ultra-gravity and capillary regions, which are wind speed dependent and result in increased wave energy levels for all increasing winds. Hasselmann, et al. (1973) , show that the Phillips equilibrium constant decreases with increasing fetch indicating long wave-short wave interaction is important in the behavior of the high frequency tail of the spectrum. 'fm is the frequency at which the peak energy occurs. 166 1318 From the observations of SKYLAB measurements obtained in Hurricane AVA, it is tempting to attribute the observed o° variations to corresponding variations in en- ergy level of wind speed dependent Bragg waves. On the basis of this limited data set, the considerable potential for errors associated with the corrections required for attenuation, relative wind direction, and backscatter due to rain, and an un- known sensitivity of o° at high wind speeds, we reject this step at this particular time. A final conclusion must await additional data obtained for high sea states during SL4 and a better estimate of azimuth dependence of a for different wind speeds and both polarizations. 5. CONCLUSIONS It can be concluded from this data set that the use of remote sensors could be a useful tool in the monitoring and study of tropical cyclones. The potential for such sensors listed by observational category is as follows: 1. Active microwave - Both cross-sectional as well as imaging microwave sys- tems can be used to map aspects of the wave field of a hurricane. High frequency systems, such as the SKYLAB RADSCAT, may have reduced utility in areas of heavy rain, while low frequency imaging systems will be limited primarily by the required high data rates. 2. Passive microwave - Aircraft and satellite measurements at 1.4, 8.35, 14, and 19.5 GHz show the higher frequencies to be capable of determining liquid mois- ture budget while the lower frequencies could be useful for determining the atmos- phere-ocean energy exchange budget because of a sensitivity to energy loss occur- ring through the wave spectrum. However, because of diminished sensitivity at 1.4 GHz, a frequency somewhat higher, but less than 6 GHz, would be more appropriate. 3. Visible: a. Satellites - Visible region imagery has been extremely useful in posi- tioning the hurricane, calculating its forward velocity, and estimating the degree of asymmetry of the hurricane. b. Coherent - Red laser light can be used with good results from low aircraft altitudes to profile surface waves despite heavy rain and spray, and the wave measurements can be used to bound the role of momentum transport to the ocean. c. Photographic - Observations of whitecap density, which is related to momentum transfer and the wave spectrum, can be obtained. Thin foam streak direc- tion relative to the eye of the hurricane could give an estimate of inflow angle of the surface winds. ACKNOWLEDGMENTS The authors are indebted to the many people from dif- ferent organizations who participated in the gathering of this data, especially the crew of SKYLAB and the NOAA C130. The personal efforts of Professors Willard Pierson and Richard Moore, and Messrs. Zack Byrns, Dean Morris, and Anthony Calio of NASA, JSC, and others who contribu- ted to the rearrangement of the SKYLAB work schedule re- quired to launch this experiment are recognized and thor- oughly appreciated. 167 1319 REFERENCES Au, B., J. Kenney, L. U. Martin, D. B. Ross, Multi-frequency radiometric measure- ments of foam and a mono-molecular slick, Proceedings of the Symposium on Remote Sensing of Environment, Willow Run Laboratories, Ann Arbor, Michigan, 1974. Cardone, V. J., Specification of the wind field distribution in the marine boundary layer for wave forecasting, Rep. TR 69-1, Geophys. Sci . Lab., New York Univ., New York, December, 1969. Crombie, D. D. , Doppler spectrum of sea-echo at 13.56 rac/s, Nature, 175, 681-682, 1955. Hasselmann, et al., Measurements of wind-wave growth and swell decay during the Joint North Sea Wave Project ( JONS WAP ) , Deut. Hydrogr. Z., Deutsches Hydrographi- sches Institut, Hamburg, FRG, 1973. Jones, W. Linwood, Personal communication, 1974. Longuet-Higgins, M. S., A nonlinear mechanism for the generation of sea waves, Proc. Roy. Soc. A., 311, 371-389, 1969. Mitsuyasu, H., R. Nakayama, T. Komori , Observations of wind and waves in Hakata Bay, Rep. Research Inst. Appl. Mech., Kyushu Univ., 19, 37-74, 1971. Phillips, 0. M. , The dynamics of the upper ocean, 261 pp., Cambridge University Press, London, 1966. Ross, D. B. , and V. J. Cardone, Laser observations of wave growth and foam density for fetch-limited 17-25 m/s winds, IEEE Trans. Geosci. Electron., GE-8(4), 326- 336, 1970. Shemdin, O. H. , R. J. Lai, A. Reece, and G. Tober, Laboratory investigations of white-caps, spray, and capillary waves, Tech. Report No. 11, Coastal and Oceano- graphic Engineering Laboratory, Univ. of Florida, Gainesville, Florida, 1972. Strong, A., Personal communication, 1973. Stilwell, D., Personal communication, 1974. Wilheit, T. , Personal communication, 1974. 168 1320 TABLE I. NOAA C130 AIRCRAFT INSTRUMENTATION Parameter Instrument Accuracy Wind Speed/Direction Sea Surface Tempera- ture Microwave Emissivity Wave Heights and Lengths Wave Length and Direction White Caps and Foam Liquid Water Content LTN-51 Inertial Navigation System Barnes PRT-5 1.4, 8.5, 14 GHz Radiometers Laser Altimeter Coherent Radar 1.35 GHz 35 mm Vertical Camera Johnson Williams Hot-Wire -2.0 kts i 1.0°C ± 1.0°K - 1% or 3" - 10% - 20% of Observation ± 15% TABLE II. SUMMARY OF SATELLITES USED TO STUDY HURRICANE AVA Satellite Imagery Type Microwave Data Use 1. ATS 2. NIMBUS-5 3. NOAA- 2 4 . SKYLAB Visible Microwave Visible Infrared Photography 5. DPP Visible Infrared 19.5 GHz HH, W 13.5 GHz HH, W HV, VH Positioning, Cloud cover Positioning, Rainfall rate Positioning, Asymmetry Cloud Cover Surface Winds Rainfall Distributions Positioning, Cloud cover, Asymmetry Cloud Heights 169 1321 OHJ C OKI) -i c a) c a CO H T3 < ~— 0 1 c -^ p> n o o ja > o •H > -H JJ 0) - x> Q 10 O 4J 3 — CTi $ X, (*) rH o r-» CO H f-{ n CT\ EC « rH ^i XO CN co H w iH u I £ C rH \ •H r-t <0 10 _ « 4H «- in < a) 3 g (0 CN + rf-K s £ ja •a1 T CO T tj rH i-H rH rH CO D 1 1 1 1 01 rH I rH I rH 1 VO rH 1 VD rH 1 00 1 (N 1 in in in m i rH 1 •>* rH 1 00 rH 1 rH r- m VO CM CN o «3- in fM o in o © © O o m CM © © 00 r» r~ r» r> 00 03 CN rH i-H rH rH »H iH <-i in © in © VD rH 00 ir a\ T* o in rH n «T © rH ri rH n *r © r~ r~ r> 00 00 00 r» r~ r- 00 CO 00 in in in in in in in in in in m in 00 00 00 00 00 00 00 00 00 00 00 00 170 1322 u ^r ;-. o iH M Eh O H 2 w H o s a. o 33 H en X o E- H Cn J 3 CM u H a U M x < W a O H m o cH ;■ u H >H J H Eh w EC X O Eh H J 2 Cm H DC CX U W a Eh < w w S w o w H a Q 2 £ o Cm 2 > H w w rH < eu w a D U 171 1323 FIGURE 2. NOAA-2 VISIBLE REGION VIEW OF PACIFIC HURRICANE AVA ON 6 JUNE 197 3. 172 1324 o < m > i-H < fa W o z < w u w H z « M « a 3 O 33 W M CJ H Q fa Z H < (J < o fa m rH fa U O £ W o 2 2 s fa Q o < D m a u g < H dj 05 H as 2 o H H J to fa a fa u • cu ro in fa a a z 3 H e> s (•93a) aaniiivT 3Aiivi3a 173 1325 « CM CM u M fa H u < • cu to O O CM O in « vo w Eh 0) Z ^ W 0) 10 u s ^4 w a) K -P Eh 3 C 05 -H < £ W o Z r-( to CO H ■«• z o O W (0 > c < t, .-H a cu D > CO CD O -P CO cr* Eh -H Z H W h 2 w a • d < CO > < < w s w « § w o CO H D X (133d) 1H0I3H 17^ 1326 NO. ATLANTIC --■ Hs = 15.22 Ft. AW A Hs = 14.87 Ft. 0 .10 .20 .30 FREQUENCY (HZ) NORTHSEA-- HS=J6.75 Ft. AVA — Hs= 16.85 Ft. 0 .10 .20 .30 FREQUENCY (HZ) to CSl" Z O in < NORTH Sf A --• Hs = 25.82 Ft. AVA Hs =27.00 Ft. FREQUENCY (HZ) FIGURE 5. HURRICANE AVA WAVE SPECTRA COMPARED TO OTHER SPECTRA OF SIMILAR ENERGY CONTENT AND WIND SPEEDS. 175 1327 o j 3 **■*. *^ < H (- < E Z- z J < < W oc Q CO ID z til. _i LU ^ ^ O a. to CO ,—» O W E z z -co CM UJ >= LU O OC O LJ CO O Z < 00 CO ** 5 to ro CM _CNJ Q H u a w a a. D cn s a u z H M Cn 2 M o frl < o o< ►J o H Pl, b O Eh « a: H i-l w < K H D W s < s (S10NX) Q33dS QNIM 176 1328 L. O i O CM _H L O O I o 0> o (0 o ID id O -J O w ro o z UJ 9 csj 2 o 00 Dj 1-3 a £h .-t W Pm W O W 2 en H z X O U H M E-> K H 03 Q 2 Q O W U M Q « 2 < H ^ 2 O a, 2 o ij D < < > _ < <£ u H faO a o o II < < U -H E < __» ^^ £ Q 00 K ^ — g Z 0 fa < _^^_^^^^ ■* ■n UJ g HERENT TED WA AT 13 IND SP O < co 3 O « E-i ,_ 1 t ►e W 2 W fcZM\ . o w s s x£ s z u X u w W fa H H < D .-1 $ - 3 CO > CO 5h < < a /5 o iJ w w at x^ < W S fa < x /* ~ s z 2 2 O Q < at E w-> oo ! • x - ► x— "^ x 1/1 IAJ IU > < IER A RRICA WAVE DEVEL " ^'x-x^ o a D a E < __ £> x D X W >< 3 z O CO .J x, X n < UJ fa fa < J O JD < X o o J fa < >■ fa 2 X O < O fa H eC fa fa CO K E-i O J 1 2 O H fa U O CO s h o a / s z M O fa 2 Q B S < 1 fa O X / - X »- o u 3 J !H < < 8 o z UJ UJ > U H O O i- o E w-i • Eh Eh oo K fa fa > X g^ „-**" * < fa a. E < X x~ O z < P •X *^ X U fa UJ < © 0 S1IND A«1VeUI9elV/UISN31NI 178 1330 fa O en X fa o u en M D fa w H U CQ < < fa fa fa x O w S fa fa fa m fa > fa fa O fa M >H fa fa O M fa S £ M O X u o fa - fa a\ fa fa 1331 OU)al (jq/uiui) 31VU NIVH o o o t N U 00S0000000000 nn§2Sc£!22!2£!i2 o o o o lO ^ IO CM (SlON>0O3n - 9£*898l - 61-8981 KM898I 6W98I fr£»Z98l 8hZ98l l£«898l 91*8981 00*8981 9W98I 0£«Z98I H9I«2.98I ooooooooooooo £iw02S£tS2!22!2 — — 2 i > OS w to • m < °3i w > w < z s < o u « m u « H « a d a w > z H M w en Q < J H a fa z < a z w m > s H H fa U O < w 2 • O O H -H EH W a o M fa ca csj (»•) 81 180 1332 VOL 79. NO 3 JOURNAL OF GEOPHYSICAL RESEARCH JANUARY 20, 1974 Observations of Oceanic Whitecaps and Their Relation to Remote Measurements of Surface Wind Speed Duncan B. Ross National Oceanic and Atmospheric Administration Atlantic Oceanographic and Meteorological Laboratories Sea-Air Interaction Laboratory, Miami. Florida 33 1 49 Vincent Cardone Department of Oceanography and Meteorology New York University. New York. New York 10453 A series of photographs of sea surface whitecap conditions for wind speeds of 10 to 25 m/s has been obtained and analyzed for areal coverage of white water. The results are in good agreement with the semiempirical calculations of Cardone, which are based on the wind speed and the development of the wave spectrum, only when the contribution of thin foam streaks oriented in the direction of the wind is neglected. Since both the actively forming whitecaps and the thin foam streaks contribute significantly, though perhaps to a differing degree, to the microwave emissivity of the sea surface, it is important that the foam streaks be included in the theory but differentiated from large whitecaps and foam patches. A simple relationship that accounts for the foam streaks based on the rate of energy transfer, the wind speed, and the wave spectrum is proposed herein. By means of empirically derived constant terms for the microwave signatures of whitecaps and foam streaks, this theory is adapted to the prediction of the in- crease in brightness temperature due to foam, with reasonable results to wind speeds of 20 m/s. The purpose of this paper is to present results of an aircraft observational program designed to determine the relationship of whitecap coverage of the ocean to environmental parameters and to test existing theoretical concepts of whitecap production. The motivation for this effort is that measurements of the microwave emissivity of the ocean are eminently suitable for space applications. Depending on the microwave band chosen, oceanographic parameters of temperature, roughness (including foam as well as rms wave slope), and salinity greatly modulate the observed emissivity or brightness temperature [e.g., Paris. 1969, 1971]. Williams [1969] first demonstrated experimentally the influence of foam on the measured microwave emissivity of the sea sur- face. Droppleman [1970] and Porter and Weniz [1971] have modeled this dependence theoretically, and others [Ross et at., 1970; Nordberg el al.. 1971; Williams. 1971] have obtained quantitative measurements of this foam dependence. Cardone [1969] utilized the freshwater whitecap observations of Monahan [1969] to develop a semiempirical theory relating freshwater whitecap density to the local wind speed and the wave spectrum. From the results obtained during the course of this study, Cardone's theory has been extended to include saltwater whitecaps and to account for the effects of thin streaks, which begin to appear at wind speeds between 10 and 12.5 m/s. Data Analysis A series of photographs has been obtained for a variety of sea conditions for wind speeds of 10-25 m/s and significant wave height conditions of 2.5-8 m. These photographs, all vertically oriented and obtained from aircraft, have been analyzed for the percentage of the surface covered by actively forming whitecaps and new foam patches and by thin foam streaks oriented in the direction of the wind. The analysis was accomplished by means of a scanning false color densitometer Copyright © 1974 by the American Geophysical Union. manufactured by Spatial Data, Inc., of Santa Barbara, California. This device scans the photograph and divides the grey scales present into 32 different levels. Each level is assigned a false color, and the result is displayed on a color television monitor. This display is then subjectively divided into three categories: actively forming whitecaps and large new foam patches, thin foam and foam streaks elongated in the direction of the wind, and background foam-free water. Selection of the lines of demarcation between each category is aided by replacing each color in turn with the color black un- til all whitecaps and foam patches are blacked out. By means of a planimeter circuit the coverage of these colors is then ob- tained. The blacking-out procedure is then continued until the foam streaks are completely filled and the areal coverage of the thin foam and streaks is obtained. The remaining colors and coverage constitute the background sea conditions. Figure 1 shows a typical photograph along with the enhanced version. Because of deficiencies in the photography it is not possible to determine the lines of demarcation precisely. In addition, spatial variability in foam conditions is significant. As a result, it is necessary to average a large number of photographs in order to obtain a usefully accurate estimate of the white water coverage. Reference Data An attempt has been made in all instances to suppress the variability in the observations due to wind speed variations with height. This is a necessary procedure, since, for example, a 15-m/s wind measured at an elevation of 10 m would measure approximately 18 m/s at 19.5-m elevation and about 22 m/s at flight altitudes of 150-400 m; therefore all winds reported here refer to an anemometer height of 20 m. For data obtained near ocean station vessel I the winds reported by the weather ship on station are used directly, since anemometers on these ships are located at 19.5 m above mean sea level. Where only flight level altitude winds are available. 444 1333 Ross and Cardone: Oceanic Whitecaps 445 Fig. I. False color enhancement of whitecap photography for surface winds of 20 m/s where whitecaps have been made black and the thin foam streaks are gold and orange. the reduction to 20 m was based on the surface boundary layer model proposed by Cardone [1969], This model allows a specification of the wind profile »-% Mf) -*(!)] where U is the wind speed, V, = (r/p)1'2, t is the surface stress, p is the air density, K = 0.4, Z is the height, Z„ is the roughness parameter, and L is the stability length, from a measurement of wind speed at a given height and the air-sea temperature difference. The wind profile stability depandence enters through the form of the function \f/ , which introduces a departure of the profile from the logarithmic. The application of surface boundary layer theory up to the low flight altitudes typical of these data appears to be justified. Table 1 presents the results of this technique for handling winds measured by means of an inertial navigation system and referenced to surface anemometer winds. Observations A tabulation of all foam cover determinations and associated environmental conditions is shown in Table 2. Ac- cording to the measured air-sea temperature differences all observations are associated with unstable stratification of varying degree. The wind speeds for the data range from 10 to 25 m/s, so that the low-level Richardson numbers, a more fundamental measure of stability, indicate only moderately unstable conditions for most observations. Hence this data set is not as useful for studying the effects of stability on foam cover as other studies at lower wind speeds that cover both positive and negative air-sea temperature differences [e.g., Monahan. 1969]. The range of fetches is quite large: the observations in the vicinity of ocean station I and southeast of Cape Fear, North Carolina, represent essentially fully developed sea conditions over the wind speed range 10-17 m/s, since observed signifi- cant wave heights were close to values given by the fully developed sea formulation of Pierson and Moskowitz [1964]. The remainder of the high-wind observations represent situations in which the fetch was limited by an upwind shoreline and seas were well below the fully developed stage. The most striking differences between these observations and those at lower wind speeds are the significant con- tributions of foam streaks to total foam cover for wind speeds above 12 m/s and the great variability in both streak and whitecap areal coverage. The former characteristic can be 1334 446 Ross and Cardone: Oceanic Whitecaps TABLE 1. Litton LTN 51 Inertial Navigator Kinds €ompared with Surface Winds Flight Reduced Measured Air-Sea Level Flight Level Surface Anemometer Temperature Win,d Speed, Altitude, Wind Speed, Wind Speed, Height, Difference, Date Location m/s ft m/s m/s m °C March 14, 1969 North Sea 25* 500 22.0* 22.7+ 20 -3 March 14, 1969 North Sea 27.3* 500 25.2* 24.7+ 20 -3 March 14, 1969 North Sea 27.8* 500 25.8* 25.4 + 20 -3 March 14, 1969 North Sea 24.2* 500 22.1* 24.0+ 20 -3 March 6, 1969 North Atlantic (I) 175 1500 15.5 16 20 March 10, 1969 North Atlantic (I) 165 500 15 16 20 -4 March 11, 1969 North Atlantic (I) 205 750 18 17 20 -3 March 13, 1969 North Atlantic (I) 165 900 13.5 13 20 -2 North Atlantic (I) 13.55 900 13.0 13 20 -2 North Atlantic (I) 16.55 1100 14.8 13 20 -2 North Atlantic (I) 15.05 500 13.5 13 20 -2 March 13, 1969 North Atlantic (J) 95 600 7 6 20 1 February 9, 1970 Hotel 16.5 150 14.8 15.5 20 -1.5 February 11, 1970 XERBI 5 150 4.5 4 10 0 February 16, 1971 XERBI 7.5 150 7 6-9 Unknown -2 February 18, 1971 Hotel 11 150 10 11 20 0 *20-min average. +Reduced geostrophic winds weighted by surface Beaufort and anemometer winds. Sl-min average. seen in Figure 1, which shows the distribution of whitecap coverage for a typical photograph. For low flight altitudes particularly the observations are subject to considerable sampling variability, since the large foam patches contribute significantly to average whitecap coverage. It is likely therefore that the 24.7- and 22.7-m/s North Sea data are biased toward low foam coverage, since no large foam patches were evident in the small number of photographs analyzed, and yet they were observed visually (by the authors) on these flights. On the other hand, the absence of large foam patches for the 20-m/s observations at short fetch is probably related to the fact that wave breaking is restricted to the relatively high frequency components in the wave spectrum, since the extremely short fetches restrict the development and saturation of larger wave components. The higher aircraft altitudes and larger area viewed per photograph may also have contributed to the smaller variability for the first two sets of photographs taken on this flight. Dependence of Foam Cover on Wind Speed As is true of most other wind-wave interaction phenomena, a meaningful dependence of foam cover on wind speed can be determined only from a set of observations representing similar stages of wave development. The five observations noted above between 10 and 17 m/s, which represent nearly fully developed seas, are thus suitable for this purpose (Figure 2). The indicated variation of whitecap coverage is in good agreement with an extensive set of observations of saltwater whitecap coverage at speeds below 10 m/s as analyzed by Monahan [1971]. The solid curve shown in the figure was also shown by Monahan [1971] to provide a good description of the highest eceanic whitecap coverage values observed below 10 m/s. This curve is one of the results of the semiempirical theory for whitecap coverage proposed by Cardone [1969] in- itially to explain the dependence of freshwater whitecap coverage on wind speed, stability, fetch, and duration but later simply extended [Ross and Cardone, 1970] to include saltwater effects in the manner proposed by Monahan [1969]. The theory is based on a simple model used to describe the growth of the wave spectrum due to energy transferred from a turbulent wind profile. The growth rate of a one-dimensional spectral wave component S(J) is defined in terms of the wind field U specified at 19.5 m above the sea surface and the fric- tion velocity Um as follows: *f> = u«, «,..,> + «,. ™[, -(0] (1) where S(J) is the spectral intensity at frequency /, A is the resonance growth term, B is the instability growth term, and Soo is the Pierson-Moskowitz fully developed spectrum. The value of the quantity Ut depends on the local wind field and the air-sea temperature difference. All nonlinear dissipative mechanisms that would act to limit growth are modeled im- plicitly by the use of the term 1 - (Sif/Soo)2, with the result that each spectral value approaches its equilibrium or saturated value given by the Pierson-Moskowitz formula. The resonance term can be thought of as an initial excita- tion mechanism, necessary to start growth for parts of the spectrum with no energy initially, but it is small in com- parison with the instability growth term,- which is responsible for nearly all the energy transfer [Phillips, 1966]. Energy transfer does not cease after a spectral component reaches its equilibrium value, and the energy thus transferred can be thought of as being dissipated through wave breaking. Whitecaps are a manifestation of wave breaking, and thus the whitecap coverage may be closely related to the energy transferred to the fully developed portion of the spectrum. This energy transfer is given by the expression E = pag •'o B(j, UJ-SiD-Sdf (2) where 5 = 1 when S S S„o, 5 = 0 when 5 > SM, pw is the den- sity of the water, g is the acceleration of gravity, and/g is the high frequency limit to the gravity wave region of the spec- trum. The Cardone hypothesis was tested with whitecap data ob- tained photographically by Monahan [1969] on the Great Lakes. The spectral growth model was used to hindcast the 1335 Ross and Cardone: Oceanic Whitecaps 447 Z Si r- « O M (N i CTi r- r- *r *r ■ T O 00 IO00 « 'JO 00 ■o tO [^ o o o CT. •o ,o Q0 fN r^ u- tO O o a. 00 © o t IO r^ o to cm r- r-~] ~~ to T _ to "7 r- to x. „ >--, to en o (N to i/i .c T oo rO •7 " O CM cm 1^- o "T u*i O t r-~ r^ \0 tj- ' o o © o o i ro to i— i O " 00 00 « OOOOOOOO*0i/10C«3-^C (--r-r-touito — oo ^-i K U5 a n nj (A s: c O 4) O (0 O x: J5 x: xi c c e e e +J«->*-»0 O 03tQ*->*->*->*->4-> << -H ~H ^H ^H ci o r- r- r- r» r* O -O ^O O >C >0 O* « ^h ■— i .— i ■— t CT>CT>CTidO^CTi - — « ~h - (^ r^ r* r-» r- -*-»-- to fN cn r\t rsi cm O « to tt ^j- C7i U -h ^, _ ^h _h ,_, 4, ^, ^xx^^ XI 01 N M J-i U M £X££££Ej3 CO fl « nj cfl OCJUCJUU4)03333D ^ o « ■ >, a. ^ >H O *-»<_> O ■o > *o a> c *-» OJ -rH w x: * T3 C O < — Q wave spectrum for each case reported from corresponding es- timates of stability, wind speed, and fetch (durations were un- known and assumed to be infinite). The energy transferred to the fully developed portion of the spectrum was then cor- related with the observed whitecap percentage. The resulting linear regression is Wr = .0.0185 + 0.893 x 103£ ergs = cm2 = sec (3) where Wf is the percent of freshwater foam density and E is the energy dissipated in breaking waves. Saltwater whitecaps are apparently more persistent than freshwater whitecaps owing to differences in the bubble-size spectra, and hence for similar conditions of wave breaking, whitecap coverage should be expected to be greater over the oceans. An approximate saltwater persistence factor of 1.5 has been suggested by Monahan and Zietlow [1969] from results of a laboratory study of comparisons of freshwater and saltwater whitecaps and was used in the solid curve shown in Figure 2. Hasselmann [1962, 1963a, b] has presented a theory on the energy balance within the wind-wave system based on non- linear wave-wave interaction that predicts that the major por- tion of energy lost through wave breaking takes place in the high-frequency end of the spectrum. Data obtained by Hasselmann el al. [1973] support the importance of wave- wave interaction in the evolution of the spectrum and indicate that wave breaking occurs predominately at frequencies higher than twice the peak energy frequency. Interpretation of the data herein incorporating their theory would not ap- preciably change the results, since these data are primarily from fully developed seas. It would, however, very likely alter the behavior of the model for growth conditions and will be considered as more data on the behavior of whitecapping at short fetches become available. The observations of the percentage of whitecap coverage (Figure 2) for wind speeds above 20 m/s lie considerably below what would be expected for both whitecap and total foam coverage on the basis of the fully developed sea con- ditions. This behavior seems to be caused by the fetch limitations associated with these data (as well as by a low bias due to sampling), since both Monahan's low-speed whitecap data and Cardone's model suggest that, for a given wind speed, whitecap coverage should increase with increasing fetch and reach a maximum for fully developed seas (Figure 3). The ratio of streak-to-whitecap coverage for this set of data appears to increase with wind speed. In Figure 4 a simple linear relationship above 9 m/s is shown to fit the data reasonably well, in view of the uncertainty in the observed ratio. Some of the data were obtained on a flight conducted on January 27, 1971, specifically designed to observe the effect of fetch on the growth of the streak and whitecap densities and the wave spectrum. The meteorological situation along with the flight track is shown in Figure 5. The behavior of the streak and whitecap densities versus fetch for this flight is shown in Figure 6. It can be seen that the growth of the significant wave height and the whitecap and streak densities are in reasonable agreement with predictions (solid curves) during the early portion of the flight. However, ap- proximately 120 km offshore there was a drastic decrease in streak density. Figure 7 is a false color enhancement of the Itos infrared image of January 27 and shows that the edge of the Gulf Stream lay at approximately this location. Whether this phenomenon is somehow related to the Gulf Stream or 1336 448 Ross and Cardone: Oceanic Whitecaps * £ * y ? i Windspeed (m/$ec) Fig. 2. Observations of whitecap density (open circles) and whitecaps plus streaks (solid triangles) compared with the predictions of Cardone [1969] (solid line). perhaps to a mesoscale lull in the wind Held is unknown, since the aircraft was not equipped with a navigation system capable of resolving small-scale changes in wind speed from the altitude flown (the aircraft Doppler navigation system is inoperative below 300 m and the Omega system does not have sufficient sensitivity). 22.5 M/Sec 20 M/Sec 175 M/Sec 2.5 M/Sec 100 200 600 Fig. 3. 300 400 500 FETCH (KM) Predictions of whitecap density versus fetch for duration un- limited conditions. The streak-to-whitecap ratio can be interpreted physically in terms of effective increase in the half-life of whitecaps in surface waters due to the presence of streak-producing cir- culations. We may speculate that these are longitudinal vor- tices [cf. Faller, 1969; McLeish, 1968] producing zones of con- vergence and are accompanied by a net downward flow of surface waters. Thus the rate at which bubbles (from breaking waves) rise is inhibited and results in an extended half-life. Bubbles transported laterally by the turbulent flow (at and below the surface) may also contribute significantly to the total foam concentration in these zones. Cardone's model calculates basically the whitecap produc- tion rate with the empiricism entering into the model through a description of the effective half-life. Thus the observed streak-to-whitecap ratios can be employed to extend the model, since, as was noted by Monahan, foam coverage is proportional to the product of the whitecap production rate and the half-life of individual whitecaps. The resulting expres- sion is FT = (1 + RSW)WS (4) where FT is the total foam density (percent of surface covered by whitecaps plus streaks), Ws is the percent of saltwater whitecap density, Rsw is the ratio of the streaks to the whitecaps, equal to -1.99 + O.25i/20, and Uw is the averaged wind speed referenced to 20 m and neutral stability conditions in meters per second. 1337 Ros1 and Cardone: Oceanic Whitecaps 449 Rs f= -1 99 + . 255 U(M/Sec) U>9 M/Sec R$-f> 0 U59 M/Sec i.i 25 15 20 WIND SPEED (M/Sec) Fig. 4. Observed ratio of streaks to whitecaps versus wind speed. Application to Microwave Emissivity Measurement Over the Ocean Ross el al. [1970] and Nordberg el at. [1971] from data ob- tained in March 1969 have shown that Kw< the increase in the microwave brightness temperature with whitecap density at the nadir viewing angle, amounts to about 1°K for a 1% change in whitecap density at 19.5 GHz. Whether this same figure is correct for the thin foam streaks (which may be largely a single-layered phenomenon at the surface) is not known exactly, although it would appear to be somewhat less. Williams [1971], investigating the phenomenon in a tank, reports that at 3-cm wavelengths the emissivity of foam- covered water is raised from 0.4 to 0.9, the foam thickness be- ing only 3 mm. This finding would suggest that the streaks might be as important as whitecaps, at least at the higher microwave frequencies. However, it is possible that a streak visible with photography is not altogether a surface phenomenon but also includes light scattered from bubbles suspended just below the surface. If this is the case, streaks and foam patches would contribute less than whitecaps to changes in the microwave emissivity. In either case the streak contribution to the measured brightness temperature increase may be represented as some constant Ks multiplied by the ratio of the streaks to the whitecaps RSw- If the whitecap and streak sensitivities are represented in this manner, the change in brightness temperature due to foam may be related to the whitecap density according to the expression A Tb — (Kw + RswKs) Ws (5) By means of the observations of A7"fl, Kw, and Ws obtained Fig. 5. Surface analysis of meteorologic situation for the fetch limited experiment of January 27, 1971, at 1200 GMT. Isobars are drawn at 3-mb intervals. 1338 450 Ross and Cardone: Oceanic Whitecaps * 1 50 100 ISO 200 F.Kh (km) Fig. 6. Observed behavior of the significant wave height, streak density, and whitecap density for the fetch limited flight of January 27, 1971. during the March 1969 experiment and the value of RSw determined herein it is possible to solve for Ks- This was done, and an average value of Ks = 0.5 was obtained. Table 3 presents results of calculations of ATB from the above equations and the photographically determined foam densities compared. to observed differences in microwave brightness temperature. Although it is recognized that some of the above results may be influenced by invalid atmospheric assumptions in the reduction of the microwave data, these influences are judged to be small, since the set of observed brightness temperature differences were carefully selected to be from similar at- mospheric conditions. Therefore it would appear from these limited data that use of (5) may give reasonable predictions for wind speeds to 20 m/s but may seriously overestimate ATB for higher winds under fetch limited conditions. Thus the thrust of future experiments must be oriented toward the higher wind fetch limited situations and multifrequency measurements of the microwave signature of foam streaks and whitecaps. Conclusions Airborne photography of the sea surface at moderate to high winds has been successfully analyzed for the total areal coverage of foam by means of a false color densitometer. Above 10 m/s, thin foam streaks oriented in the wind direc- tion contribute increasingly to total coverage, so that at speeds of 20 m/s they account for about 70% of the total coverage. The ratio of streak-to-whitecap areal coverage appears to be largely a function of the local wind field for the data set analyzed in this study. For the nearly fully developed sea cases analyzed the coverage of actively forming analyzed in this study. For the nearly fully developed sea cases analyzed the coverage of actively forming foam patches (whitecaps) is in good agreement with the model proposed by Cardone and with measurements at lower wind speeds obtained by ship- board photography. The variability in foam coverage is large on the scale of the area viewed in a given photograph (about 1000 m2 at an altitude of 100 m), and many photographs must therefore be analyzed for each case. For well-developed seas at speeds above 10 m/s, very large foam patches may nearly fill the view of a given photograph, whereas an adjacent patch of sea will be essentially foam free. However, at spacecvft altitudes the area of sea surface (footprint) vie" 1 by microwave sensors will more closely represent the synoptic TABLE 3. Comparison of Calculated and Observed Brightness Temperatures Calculated ATg, °K Obsei Wind Speed, Ro ss-Cardone Observations of •ved m/s Model Whitecaps and Streaks 42'B. "K 13 5.5 6.0 7 0 16 14.5 10.0 12 0 20 18.0 15.0 18 0 25 70.0 15.0 22 0 1339 Ross and Cardone: Oceanic Whitecaps 451 Fig. 7. False color enhancement of Itos high-resolution infrared radiometer image of January 27, 1971, showing the warm Gulf Stream in red and light blue and cooler shelf waters in black. scale. The limited application of our whitecap observations to ■ microwave observations suggests that at the higher wind speeds a spaceborne microwave radiometer (such as the one flown by Skylab) can be utilized to determine wind speed near the sea surface. Acknowledgments. The authors are indebted to the many people and organizations who supplied data for this study and assisted injhe conduct of the various experiments. These include the NOAA* Research Flight Facility, which flew the low-level (100 m) experiment, NASA Ames, JSC, and GSFC, which contributed much of the photography and all of the microwave data, and Bruce Gritton, who greatly aided in the processing of the data. This work was supported by NASA funds disseminated by the NOAA National Environmental Satellite Service and the SPOC group of the U.S. Naval Oceanographic Office. References Cardone, V. J., Specification of the wind field distribution in the marine boundary layer for wave forecasting, Rep. TR 69-1, Geophys. Sci. Lab., New York Univ., New York, December 1969. Droppleman, J. D., Apparent microwave emissivity of sea- foam, J. Geophys. Res.. 75. 696-698, 1970. 1340 452 Ross and Cardone: Oceanic Whitecaps Faller, A J., The generation of Langmuir circulations by the eddy pressure of surface waves, Limnoi Oceanogr.. 14. 504-513, 1969. Hasselmann, K., On the non-linear energy transfer in a gravity-wave spectrum, I, General theory, J. Fluid Mech . 12. 481-500, 1962. Hasselmann, K., On the non-linear energy transfer in a gravity-wave spectrum, 2, Conversation theorems, wave-particle cor- respondence, irreversibility, J. Fluid Mech.. 15. 273-281, 1963a Hasselmann, K... On the non-linear energy transfer in a gravity-wave spectrum, 3, Computation of the energy flux and swell-sea interac- tion for a Neumann spectrum, J. Fluid Mech . 15. 385-398, 1963ft. Hasselmann, K., et al.. Measurements of wind-wave growth and swell decay during the Joint North Sea Wave Project (Jonswap), Deul. Hydrogr. Z . 26(5), in press, 1973. McLeish, W , On the mechanism of wind-slick generation, Deep Sea Res.. 15. 461^169, 1968. Monahan, E. C Fresh water whitecaps, J. Almos. Sci.. 26(9), 1026-1029, 1969. Monahan, E. C Oceanic whitecaps, J. Phys. Oceanogr., I, 139-144, 1971. Monahan, E. C, and C. R. Zietlow, Laboratory comparisons of freshwater and saltwater whitecaps, J. Geophys. Res.. 74, 6961-6966, 1969. Nordberg, W. J. Conaway, D. B. Ross, and T. Wilheit, Measurements of microwave emission from a foam-covered, wind- driven sea, J. Almos. Sci.. 2S(3), 429-435, 1971. Paris, J. F., Microwave radiometry and its application to marine meteorology and oceanography, Ref. 69-11, 210 pp., Dep. of Oceanogr., Texas A&M Univ., College Station, 1969. Paris, J. F., Transfer of thermal microwaves in the atmosphere, in- terim report, 257 pp., Dep. of Meteorol., Texas A&M Univ., College Station, May 1971. Phillips, O. M., The Dynamics of the Upper Ocean, 261 pp., Cam- bridge University Press, London, 1966. Pierson, W. J., and L. Moskowitz, A proposed spectral form for fully developed wind seas based on the similarity theory of S. A. Kitaigorodskii, J. Geophys. Res.. 69. 5181-5190, 1964. Porter, R. A., and F. J. Wentz Ml, Microwave radiometric study of ocean surface characteristics, final report, 250 pp.. Radiometric Technology, Inc., Wakefield, Mass., July 30, 1971. Ross, D. B., and V. J. Cardone, Laser observations of wave growth and foam density for fetch-limited 25 m/sec winds, NASA Rep. MSC-03742. pp. 85-1-85-20, December 1970 Ross, D. B., J. Conaway, and V. J. Cardone, Laser and microwave observations of sea-surface conditions for fetch-limited 17- to 25- m/s winds, IEEE Trans. Geosci. Electron., GE-8(4), 326-336, 1970. Williams, G. F., Jr., Microwave radiometry of the ocean and the possibility of marine wind velocity determination from satellite observations, J Geophys. Res.. 74. 4591-4594, 1968. Williams, G. F., Jr., Microwave emissivity measurements of bubbles and foam, IEEE Trans Geosci. Electron . GE-9. 221, 1971. (Received March 1, 1973: revised August 16, 1973.) 1341 Reprinted from Journal of Atmospheric Sciences, Vol. 31, No. 2, March 1974, pp. 598-599 American Meteorological Society Printed in U. S. A. Reply William D. Scott1 Atlantic Oceanographic and Meteorological Laboratories, NOAA, Miami, Fla. Zev Levin Dept. of Environmental Sciences, Tel-Aviv University, Ramat-Aviv, Israel 13 August 1973 It is gratifying to hear that our experimental results (Scott and Levin, 1971) have been further corroborated. Indeed, Aufdermaur and Johnson (1972) reported similar results for the case of small supercooled water drops, and Mason (1972) now considers polarization charging (also called induction and influence charging) as perhaps the most important general charging mechanism (following Sartor, 1961). However, since Muchnik's experiments preceded our experiments, they should present a more independent check. Nevertheless, it appears that some of our interpre- tations of the results are somewhat different than Muchnik's: The linear relationship between charge and electric field which Muchnik observed in the laboratory during collisions between spheroidal particles was not apparent in measurements with natural snowflakes above electric fields of 50 V cm-1. At higher fields the charging was more than would be predicted by a linear relationship. This may seem a small point but the ultimate effectiveness of polarization charging in clouds may depend upon this increased charging at high electric fields. The suggestion that corona or spark discharge is important during the collisions is interesting, but 1 Present affiliation : Department of Environmental Sciences, Tel-Aviv University, Ramat-Aviv, Israel. complicated, and depends upon the effective penetration of the intervening air layer by the discharge, the distribution of surface charge, and the shape of the colliding objects as well as the bulk and surface conduc- tivity and dielectric constants. Remember that surfaces of ice crystals, generally speaking, are not smooth and the crystals can have a very complex distribution of electric charge on their surfaces, with higher concentra- tions of charge on their sharp features. Hence, a dis- charge would bleed off charge only from a single point, leaving the major portion of the charge. This charge would most likely move along the ice surface according as the surface conductivity and dielectric constant of ice, quantities affected by impurities. In fact, though, the effective conductivity in most natural cases is sufficiently large to allow the full effect of polarization charging. We believe that the confusion arises from Muchnik's use of only smooth ice spheres and water drops. In this case discharge effects as well as surface conduction and relaxation times could be quite different. Note that if ice of high purity is used and the experi- ments are performed at a sufficiently low temperature, polarization charging can be suppressed. Sartor (1970) showed just such suppressed charging in data compiled in recent years. Since Latham and Mason used ice of high purity, they may well have had this effect. 1342 5 oq JOURNAL OF THE ATMOSPHERIC SCIENCES Voi.l'MF .11 Several other effects may also be responsible for the observations by Latham and Mason of little polari- zation charging. For instance, the sliding effect men- tioned by Muchnik would result in greatly diminished charging, but such an occurrence is highly improbable between irregular surfaces. The observations by Much- nik of diminished charging during collisions between water drops and ice spheres may be the effect in which the experimental parameters are such that the water drop simply envelopes the sphere and leaves with zero charge; however, this occurrence would normally be accompanied by splashing and breakup and should produce some charging. With hydrometeors of the appropriate size and charge, it is possible that the smaller pieces are simply captured in the wake of the larger piece, with no charging. Collisions have even been observed in which drops of 1 mm size simply rotated about each other with a reversal in sign of the separated charge (Montgomery and Dawson, 1969). In specific instances there is no doubt that polarization charging can be diminished or reversed. However, the overall power of the polarization charging mechanism is its generality; some collisions may not produce effective charging but most collisions do. Hence, the suggestions presented by Muchnik may explain the discrepancy between our data and those of Latham and Mason though the differences could just as well be due to the better measuring capabilities brought on by recent electronic developments (see Scott, 1972). We feel that there are many possible explanations but, more important, we now have ample evidence to sup- port polarization charging as a general charging mechanism. Remember that our paper (Scott and Levin, 1970) was only intended to explain charging effects in fully glaciated clouds such as observed by Stow (1969). Nonetheless, since then we have done more experimental and theoretical work including effects of water drops (Levin, 1970, 1971; Levin and Hobbs; 1971, Levin and Scott, 1972). As a result, we feel that polarization charging can be effective, more or less, during collisions of all types of solid and liquid hydrometeors, in all portions of the cloud, and at all stages of cloud develop- ment. In the case of ice-ice interactions, the statement by Muchnik that the cloud has a high conductivity and cannot sustain a high charging rate applies to most charging mechanisms. Certainly, as is shown by Evans (1969), the presence of such a highly conducting region depends upon the stage of cloud development and the magnitude of the electric field. Hence, the effective electrification may be diminished but not necessarily by a substantial amount. As was emphasized by Muchnik, the effect of positive feedback, whereby charging produces a greater effective field which, in turn, produces further charging, lends power to the overall mechanism as was earl}- recognized by Elster and Geitel (see Mason, 1971). However, one of many complicating factors, not considered by Muchnik, is the concept of levitation as first mentioned by Kamra (1970, 1971). As the field builds up and the hydrometeors become charged, they tend to be sus- pended in the electric field, and further polarization charging ceases. In this case, as with all polarization charging effects, particle size and character as well as the types of collisions are important. Indeed, recent numerical calculations (Ziv and Levin, 1973) have shown that the maximum electric field in the cloud can actually be increased by a decreased effect of polariza- tion charging. The effect is this: during the formation of the larger hydrometeors, if the polarization charge on each particle is small enough that levitation does not occur early, the particle can fall and grow to such a size that a higher electric force is required for levitation. In their fall, then, a larger electric field is produced through added collisions and the action of polarization charging. REFERENCES Aufdermaur, A. N., and D. A. Johnson, 1972: Charge separation due to riming in an electric field. Quart. J . Roy. Meteor. Soc, 98, 369-382. Evans, W. H., 1969: Electric fields and conductivity in thunder- clouds. J. Geophys. Res., 74, 939-948. Kamra, A. K., 1970: Effect of electric field on charge separation by the falling precipitation mechanism in thunderclouds. J. Atmos. Sci., 27, 1182-1185. , 1971 : Replv to comments by Anderson and Frier. /, Atmos. Sci., 28, 820. Latham, J., and B. J. Mason, 1962: Electrical charging of hail pellets in a polarizing field. Proc. Roy. Soc. London, A266, 387-401. Levin, Z., 1970: Splashing of water drops: A study of the hydro- dynamics and charge separation. Ph.D. thesis, L'niversity of Washington. , 1971: Charge separation by splashing of naturally falling raindrops. J. Atmos. Sci., 28, 543-548. , and P. V. Hobbs, 1971: Splashing of water drops on solid and wetted surfaces: Hydrodynamics and charge separation. Phil. Trans. Roy. Soc. London, A269, 555-585. , and W. D. Scott, 1972 : The polarization charging effect and thundercloud electrification. Nature, 240, 232-233. Mason, B. J., 1971: The Physics of Clouds, 2nd ed. London, Oxford University, p. 521. , 1972: The physics of the thunderstorm. Proc. Roy. Soc. London, A327, 433-466. Montgomery, D. N., and G. A. Dawson, 1969 : Collisional charging of water drops. J. Geophys. Res., 74, 962-972. Sartor, J. D., 1961: Calculations of cloud electrification based on a general charge generating mechanism. J. Geophys. Res., 66, 831-838. , 1970: General thunderstorm electrification. National Center for Atmospheric Research, Boulder, Colo., 99 pages. Scott, \V. D., 1972: Details for constructing a miniature solid state electrometer probe. Rev. Sci. Inst., 43, 152-153. , and Z. Levin, 1970: The effect of potential gradient on the charge separation during interactions of snow crystal with an ice sphere. /. Atmos. Sci., 27, 463^473. Stow, C. D., 1969: On the prevention of lightning. Bull. Amer. Meteor. Soc, 50, 514-520. Ziv, A., and Z. Levin, 1973: Thundercloud electrification by the polarization mechanism. Submitted to J. Atmos. Sci. 1343 ;?** #r* JF"*&, !S» 3 efa v^ 9 P^ S C id jss pt5« a r\ h >u.a ^ *& £ d -.* -*-&-*' %^-' va $ ■iS.-" "■31 ffi "T^a t ^ ~"~% £'3S v~^\ q r?», {*% ?":a ps * nr^ j Ji. 2 - it m. t ,.* i oi ■ ^ill i- ••13 ■ -i ~-\ sua & 4 3 PAPER NO. 6 ANALYSIS OF THE CONVAIR-990 PASSIVE MICROWAVE OBSERVATIONS OF THE SEA STATES DURING THE BERING SEA EXPERIMENT William J. Webster. Jr.* Thomas T. Wilheit* Duncan B. Ross Per Gloersen* \ J ♦National Aeronautics and Space Administration. Goddard Space Flight Center, Greenbelt, Maryland 20771 ^National Oceanic and Atmospheric Administration, Atlantic Ocean- ographic and Meteorological Laboratories, Miami, Florida 33149 GODDARD SPACE FLIGHT CENTER GREENBELT, MARYLAND WAY 1974 165 PKtPrJi \'T 1344 Paper No. G ANALYSIS OF THE CONVAIR-9S0 PASSIVE MICROWAVE OBSERVATIONS OF THE SEA STATES DURING THE BERING SEA EXPERIMENT William J. Webster, Jr. Thomas T. Wilheit Duncan B. Ross Per Gloersen ABSTRACT Observations of microwave brightness temperature made over the wavelength range from 21 cm to 0.81 cm show that the variation of brightness temperature with increasing wind speed is linear and is primarily a function of the percentage white water coverage. The frequency dependence of the wind speed sensitivities for winds greater than 10 m/s shows that the sea-air boundary layer (i.e. the white water layer) is a thin dielectric layer. The nadir angle dependence of the brightness temperature at 1.55 cm shows that, for horizontal polarization, the wind speed dependence becomes stronger as the angle of observation increases from nadir. The variation of brightness temperature with distance from the edge of the ice (fetch) shows that the brightness temperature decreases with decreasing fetch and that this change is primarily due to the decrease in areal coverage of thin foam streaks. A three-component model for the sea-air boundary layer based on the passive microwave observations is proposed. 166 1345 ANALYSIS OF THE COXY AIR -990 PASSIVE MICROWAVE OBSERVATIONS OF THE SEA STATES DURING THE BERING SEA EXPERIMENT 6.1 INTRODUCTION The Option A and B flights of the Convair-990 during the Bering Sea Experi- ment have provided data on the brightness temperature of the sea (Tg ea ) over a wide range of ocean conditions and over a wide span of wavelengths. In Table 6.1, the radiometers used in this study are listed. From these observa- tions, we have deduced the wind speed sensitivity and the white water sensitivity of the individual wavelengths and polarizations. Numerous aircraft and ocean platform observations have demonstrated the variation of T sea with ocean surface conditions. Aircraft measurements at 1.55 cm by Nordberg et al (1969) suggested a strong variation of brightness temperature with increasing sea roughness. Subsequent observations (Nordberg, et al, 1971) showed that, above the critical wind speed for the formation of white caps (Munk, 1947), T^3 varies approximately linearly with wind speed and that this increase is due primarily to the change of the white water coverage. It was also suggested that there is a different dependence on wind speed for viewing angles off nadir. In an attempt to separate the white water influence from changes in wave structure, Hollinger (1970, 1971) made multi -frequency observations from an ocean platform. He specifically excluded actively breaking waves from his measurements. He concluded that, while horizontal polarization shows a substantial wind effect, there is only a very small effect for vertical polarization or near nadir observations. 167 1346 In what follows, we show that the data obtained during the Bering Sea Ex- periment confirm and extend the results reported previously. We find that for nadir and vertical polarization observations the variation of white water cover- age dominates the change in observed brightness temperatures. The data permits a determination of some of the properties of the boundary layer between the water and the air. The data also show the influence of fetch when high wind speeds must be considered. It is apparent that a neglect of fetch in the reduction of observa- tions can contribute an important error in the implied wind speed. 6.2 THE VARIATION OF BRIGHTNESS TEMPERATURE WITH WIND SPEED We have examined the variation of TBsea with wind speed (U1S5 ) measured at 155 m aircraft altitude for each wavelength and polarization for wind speeds greater than 10 m/s and under fully developed conditions. In order to reduce the importance of transient features, the observations were averaged over periods much longer than the time constants of the radiometers, typicall}' 4 minutes. To minimize the contribution from the atmosphere below the aircraft and to avoid a contribution from aircraft reflections, only data taken at about 155 m altitude were used. The component of the atmospheric emission (TBsky ) reflected from the ocean surface makes an important systematic contribution to the observed TBsea. We have made use of simultaneous measurements of TBky at 0.81 cm to remove the reflected sky component from the down-viewing measurements. T £k* for each frequency was obtained by assuming the sky brightness temperature was determined by clouds and therefore scaling the 0.81 cm measurement by a square law dependence on wavelength. This scaling appears to be good except 168 1347 near the water vapor resonance at 1.35 cm. Mean reflectivities were calculated using the Fresnel equations, the dielectric constant data of Lane and Saxton (1952) and assuming a specular sea. A sea temperature of 0°C was assumed. The assumptions made in this calculation should not make an error of more than 0.5°K in the reflected TBsea calculation at 0.81 cm, less at longer wave- lengths. It should be noted that the specular sea assumption is equivalent to assuming that large angle scattering is unimportant for ail wind speeds. This assumption will be less accurate at the higher wind speeds. The corrected data are the products of the surface emissivity and thermo- dynamic temperature. These data, weighted directly by the number of minutes in the averages, were fit to a line by the method of least squares. Table 6.2 presents the slopes of the least squares lines and the formal standard error of the slopes. Examples of these curves are given in Figures 6.1 and 6.2. Fig- ure 6.1 gives TBsea vs U155 for 1.55 cm. nadir, and 38° horizontal and for 21 cm. Figure 6.2 gives 0.81 cm H and V and 6.0 cm H and V. Each figure also contains the result of a 6 minute average from 23/21 February when the wind speed was very low (5.1 m/s) and there was virtually no white water present. These low wind speed points were not included in the analysis but indicate the difference in the wind speed effect for wind speeds above and below 7 m/s. In Figure 6.3, we plot the slopes of the Tg ea vs U155 curves as a function of frequency. Note that a smooth curve passing through the nadir and vertical polarization measurements would rise from 1.4 GHz (21 cm) to roughly 11 GHz (2.7 cm). Theoretical studies (Stogryn, 1967, Wu and Fung, 1972) as well as Hollinger's (1970, 1971) experimental results indicate that the nadir and vertical polarization data should represent primarily a white water effect. The horizontal 169 1348 polarization dita combine the white water effect with a substantial roughness contribution. Figure 6.4 gives the calculated emissivity curve whose shape is consistent with the sensitivity curve of Figure 6.3. The emissivity curve was calculated assuming that the index of refraction of the sea-air boundary layer, which we identify with the white water, varies linearly from the value for water to that for air in a distance of 1.5 mm. The calculation was performed by dividing the interface layer into 100 steps and solving the boundary value problem for each edge in succession. The actual depth of the layer is most important in determin- ing the rise in the sensitivity curve of Figure 6.3. The 1.5 mm layer depth is very small compared to the apparent depth of sea foam and it is of interest to speculate on its physical significance. Labora- tory measurements (Williams, 1971) and theoretical calculations (Droppleman, 1970) show that scattering or attenuation within the foam is unimportant. These studies suggested that the most important factor is the distortion of the water surface at the interstices of the bubbles. Thus the 1.5 mm depth refers to the region immediately above the ocean surface where sea water is being lifted by surface tension or turbulent processes. 6.3 POLARIZATION AND ANGLE DEPENDENCE OF TBsea Because of the presence of white water and the change of wave structure, the angular dependence of the emission from a smooth sea is different from that for a rough, foam3r sea. Data from the 1.55 cm scanning radiometer, which covers nadir angles from 0° to 50°, illustrates this. In Figure 6.5, we plot the angle dependence of TBsea for a low wind speed case (23/24 February) and a high wind speed case (7/8 March). These measurements were corrected for 170 1349 reflected sky emission as described above. Note that the decrease of brightness temperature with nadir angle is much greater for the low wind speed case. The presence of roughness and white water in the high wind speed case has decreased the angle dependence as well as increased the T|ea at nadir. Theoretical calculations of the emission from a rough but not foamy sea show that the dependence on changing wave structure is greater for horizontal polarization (Wu and Fung, 1972). In agreement with these predictions, Table 2 shows that the slopes of the TBsea vs wind speed curves are highest for horizontal polarization. Because the white water signature is only weakly polarized and since the wave contribution is negligible for vertical polarization, the increase in the slope for the horizontal polarizations over the slope for vertical polariza- tion is due to changing wave structure. This increase is in approximate agree- ment with the foam-free measurements (Hollinger, 1971). Further, the residual slope follows the predicted trend of increasing toward higher frequencies (Wu and Fung, 1972). 6.4 THE INFLUENCE OF FETCH, WAVE STRUCTURE AND WHITE WATER VARIATION During the flights of 23/24 February and 7/8 March, we obtained extensive observations at low (about 155 m) altitude. In each case, approximately one hour of data was obtained along a track at an angle of about 30° to the edge of the ice from a point about 300 km seaward to slightly north of the ice edge. The flight of 23/24 February was made under conditions of light (about 5 m/s) winds. The radar survey made by the USSR aircraft indicates some swell and very little wind wave activity within the test area at this time (Martsinkevitch, L. M., 1973, Personal Communication). The microwave data 171 1350 shows liitle or no change as the aircraft approached the edge of the ice. Fig- ures 6.6 and 6.7 show one minute averages for several of the radiometers during this period. Note that the data are corrected for reflected sky emission as de- scribed previously. As the edge of the ice is approached, there does appear to be a very slight change in TBsea at each frequency. The observed infrared temperature of the sea surface decreases by about three degrees during this period, which is ade- quate to account for the change in TBsca . Note that the decrease in the thermo- dynamic temperature causes an increase in the brightness temperature at 0.81 cm. This is because the emissivity is a function of temperature and at 0.81 cm de- creases fast enough with increasing temperature that d(eTs )/dTs < 0. The results are summarized in Table 6.3. The calculated temperature sensitivities are based on the Lane and Saxton (1952) dielectric constant measurements, while the ob- served sensitivities were determined by a least squares analysis of TBsea as a function of the infrared temperature corrected for aircraft altitude. The table confirms the predicted trend and shows that the highest sensitivity to surface temperature is for 6.0 cm, vertical polarization. The flight of 7/8 March yielded the highest wind speeds and foam coverages observed during the joint experiment. Table 6.3 gives the white water coverage obtained from nadir camera observations using the method of Ross and Cardone (1974). The table also gives the wind speed at 20 m altitude assuming a loga- rithmic profile (Cardone, 1969) between the aircraft and the sea and using the wind speeds determined from the aircraft inertial navigation system at about 155 m altitude averaged over one minute. 1351 As the table shows, the total white water coverage begins to decrease after approximately OO*1].^. The percentage of white caps remains roughly constant over most of the interval and it is primarily the steaks which decreased. Dur- ing the same interval, the winds at 20 m altitude rose from 22.6 m/s to 24.7 m/s. The infrared temperature remains constant at about +0.5°C until severe spray and precipitation invalidate the measurements. Based on the 23/24 February data, we do not expect an ocean surface temperature gradient of more than 30°C from the beginning of the 155 m track to the ice edge. The USSR radar survey of the area (Belousov et al, 1973) showed that wind waves were dominant over swell during the March 7/8 flight. Since the wind was blowing nearly perpendicular to the ice edge, the 155 meter track was obtained for a fetch which decreased continuously from about 250 km to 0 km. This changing fetch yielded changes in the wave structure and the white water in a measurable way. Therefore, we can use the polarization properties of the emis- sion from the sea to separate the dependence on white water from the dependence on waves. In Table 6.4, we give the sensitivities of TBsea to observed white water. The sensitivities were determined by a least squares analysis of the corrected T|ea for each wavelength and polarization as a function of the total white water cover- age observed photographically. The nadir and vertical polarization sensitivities follow a similar wavelength dependence to the wind speed sensitivities. In this case, the data show the properties of the sea-air boundary layer without the confusion of a large change in wind speed. The total white water values from Table 6.3 have been plotted in Figure 6.8. Note the essentially linear relationship between fetch and percentage white water 173 1352 at least up to 250 km (00;'0-i::'). Similarly, some of the TEsea measurements are also plotted in Figures 6.8 and 6.9. Although the visible white water percentage changed by about 40. r, only 3?c being due to actively breaking waves, the largest decrease in TBsea is about 5°K. That is about half of the wind and foam effects remained at the zero fetch limit even though the visible white water had nearly disappeared (except at 21 cm). This suggests that aircraft photographic meas- urements of the visible white water cannot determine the total contribution to TBS" in a fetch limited case. Some of the white water contributing to Tgea may not be visible photographically. Alternatively, the decrease in white water may be balanced by an increase in the short wave contribution. During the 155 meter pass, the surface winds (U20 ) rose from 22.6 to 24.7 m/s as the aircraft approached the ice. If we ignore fetch, rising wind speed would contribute an increase of about 2°K for horizontal polarization over the period of the decreasing white water observations. Since the white water cover- age changed by about 40%, this wind speed change would appear as a white water sensitivity of -0.05°K/percent. If we also ignore the very small roughness effect predicted for vertical polarization (VVu and Fung, 1972), the combination of the vertical polarization measurements and the wind speed rise predict a horizontal polarization sensitivity of about 0.05°K/percent. This is as observed except for 0.81 cm. We speculate that the short waves, which are important for the wave slope influence on TBsea , should be fully developed almost immediately. If so, the data indicate a decrease in at least part of the amplitude spectrum of the short gravity and capillary waves with increasing fetch. The decrease seems to be in response to the variation of the wind speed with fetch. This is consistent with 174 1353 the results of Hasselman et al (1973), who attributed the observed reduction of high frequency wave energy with increasing fetch to non-linear interactions with the longer growing waves. 6.5 DISCUSSION From analysis of the Convair-990 observations, we find: 1. The variation of TBsea with wind speed (U155) is linear between 11 m/s and 27 m/s under fully developed conditions. Below the critical wind speed for the formation of white water, the data suggest a variation with a much smaller slope. 2. The nadir angle dependence of Tp ea at 1.55 cm shows that the strength of the wind speed effect increases as the nadir angle increases. 3. The low wind speed observations show no dependence on fetch, while the high wind speed observations show that TBsea varies through the Change in white water coverage and wave structure with fetch. 4. The frequency dependence of the wind speed sensitivities and of the white water sensitivities is consistent with a model in which the sea-air boundary layer is a dielectric layer about 1.5 mm thick. Very limited observations have suggested that white caps have a different emissivity from streaks (Nordberg et al, 1971; Ross et al, 1970). Observa- tions of simulated foam (Williams, 1971) and calculations of the emissivity of a foam layer as a function of depth (Droppleman, 1970) support this suggestion. The Convair-990 microwave data do not allow us to directly separate the white caps from the streaks in an unambiguous way, however. Since the white cap coverage was only about 5% over the bulk of the 7/8 March observations, even a unit emissivity for the white caps would not account 175 1354 for the effect observed at wavelengths shorter than 6 cm. The important part of the white water for ite short wavelength microwave observations must be the thin streaks. In many cases, the streaks are so thin as to escape photographic detection. Thus, the following model (see Figure 6.10) emerges: the interface be- tween the sea.and the air is a dielectric layer with thick spots (several cm), thin spots (about 1.5 mm) and voids. The thick spots correspond to the white caps and the thin spots correspond to the streaks. The total area covered by the thick and thin spots increases as the wind speeds increases; the total area of the thin spots in much greater than the thick spots. In addition to the change of the areal coverage of the white water components with wind speed, the small scale roughness of the sea increases at least up to 23 rn/s for fully developed seas. The small scale roughness spectrum, however, appears to be fetch de- pendent, decreasing with increasing fetch. ACKNOWLEDGMENT We acknowledge with thanks the careful and patient work of E. V. Petersen and the crew of the CV-990 from the NASA/Ames Airborne Science Office. The loss of some of the crew on April 12, 1973 in a crash of that aircraft is deeply regretted. 176 1355 BIBLIOGRAPHY Belousov, P., Zhilko, E. O., Zagorodnikov, H. H., Kornienko, V. L, Loshchidov, V. S. and Chel'shev, K. B., 1973, in Results of the Soviet -American Experi- ment, A. I. Voyeykov Main Geophysical Observatory, Leningrad, USSR. Cardone, V. J., 1969, Rep. TR69-1, Geophys. Sci. Lab. N.Y.U. Droppleman, J. D., 1970, J.G.R., 75, 696. Hasselman, K.; Barnett, T. P., Bouws, E., Carlson, H., Cartwright, D. E., Enke, ^J. A., Grenapp, H., Hasselman, D. E., Kruseman, P., Meerbnrg, A., Miiller , P., Olbers, D. J., Richter, K., Sell, W., and Walden, H., 1973, Enganzungsheft zur Deutschen Hydrographischen Zeitschrift, Reih A Nr 12, Deutsches Hydr ogr aphis ches Institut, Hamburg, BDR. Hollinger, J. P., 1970, J.G.R., 75, 5209. Hollinger, J. P., 1971, I.E.E.E. Trans. Geosci. Elect., GE-9, 169. Lane, J. and Saxton, J., 1952, Proc. Rcy. Soc, A213, 531. Munk, W. H., 1947, Journ. Marine Res., 6, 203. Nordberg, W., Conavvay, J. and Thaddeus, P., 1969, Q.J.R. Meteor. Soc, 95, 403. Nordberg, W., Conaway, J., Ross, D. B., and Wilheit, T. T., 1971, J. Atmos. Sci., 23, 429. Ross, D. B., Cardone, V. J., and Conaway, J. W., Jr., 1970, I.E.E.E. Trans. Geosci. Elect., GE-8, 326. 177 1356 Rc-3; D. E. and Cardo::e, V., 1974, J.G.R., 79, 444. Stogryn, A., 1967, I.E.E.E. Trans. Ant. Prop., AP-15, 273. Williams, G., Jr., 1971, I.E.E.E. Trans. Geosci. Elect., GE-9, 24. Wu, S. T. and Fung, A. K., 1972, J.G.R., Tl_, 5917. 178 1357 Table 6.1 Microwave Radiometers Used in Sea State Study Wavelength Frequency Polarization Nadir Angle Sensitivity 21.0 cm 1.42 Nadir 0° 2.5°K (1 second) 6.0 cm 4.99 Vertical 38° 2.0°K (1 second) 6.0 cm 4.99 Horizontal 38° 10.0°K (1 second) 2.8 cm 10.69 Vertical 38° 3.0°K (1 second) 2.8 cm 10.69 Horizontal 38° 3.0°K (1 second) 1.55 cm 19.35 Horizontal scanner 2.0°K (47 ms) 0.95 cm 31.4 Nadir 0° 0.3°K (1 second) 0.81 cm 37.0 Vertical 38° 2.4°K (1 second) 0.81 cm 37.0 Horizontal 38° 2.4°K (1 second) 0.81 cm 37.0 Zenith 115° 0.9°K (1 second) 179 1358 Table 6.2 .Measured Slooes of Wind Soeed vs. Brightness Temoerature Curves Wavelength (cm) Polarization Slope °K meter per second 21.0 6.0 6.0 2.S 2.8 1.55 1.55 1.55 1.55 0.95 0.81 0.81 Nadir V-38° H-38° V-38° H-38° Nadir H-12° H-24° H-38° Nadir V-38° H-38° 0.205 ± 0.051 0.450 ± 0.056 0.989 ± 0.095 0.659 ± 0.172 1.180 ± 0.042 0.860 ± 0.103 0.931 ± 0.126 0.999 ± 0.075 1.016 ± 0.097 0.739 ± 0.095 0.535 ± 0.087 1.257 ± 0.293 180 1359 Table 6.3 Comparison of Observed and Predicted Temperature Dependence AT, AT Wavelength (cm) Polarization AT s AT s Observed Predicted N 0.3 ± 0.4 -0.05 V-3S° 0.8 ± 0.6 +0.5 H-38' 3.8 ± 3.7 +0.3 V-33° 0.8 ± 0.7 +0.4 H-38° 1.4 ± 1.5 +0.2 N 0.5 ± 0.7 +0.02 N -0.6 ± 0.4 -0.02 V-38° -2.4 ± 1.7 -0.3 H-38° -1.2 ± 0.8 -0.3 21.0 6.0 6.0 2.8 2.8 1.55 0.95 0.81 0.81 181 1360 Table 6.4 White Water Analysis 7/8 March Low Pass Time (GMT) White Caps <%) White Caps and Streaks (%) 20 m Wind Speed (m/s) Time (GMT) White Caps <%) White Caps and Streaks (%) 20 m Wind Speed (m/s) 0000:00 2.9 35.2 22.6 0020:00 12.1 24.6 0001:00 1.4 25.8 0021:00 8.0 20.1 0002:00 4.6 35.0 0022:00 2.0 12.4 0003:00 6.2 37.0 0023:00 6.0 21.6 23.7 0004:00 6.0 42.2 22.6 0024:00 3.4 22.7 0005:00 2.5 40.4 0025:00 2.3 25.2 0006:00 2.5 37.5 0026:00 1.4 11.4 24.2 0007:00 1.7 36.7 0027:00 2.5 14.3 24.2 0008:00 2.0 30.9 22.6 0028:00 2.1 11.5 0009:00 2.6 44.6 0029:00 1.9 15.0 0010:00 8.2 36.3 22.6 0030:00 2.3 10.5 0011:00 4.3 39.7 0031:00 3.1 7.7 0012:00 1.6 40.5 0032:00 1.8 5.4 24.2 0013:00 3.7 37.7 22.6 0033:00 1.85 6.4 0014:00 1.3 28.5 0034:00 1.9 12.2 0015:00 7.3 25.5 0035:00 2.6 3.7 0016:00 5.2 31.7 0036:00 3.9 8.1 0017:00 0.5 26.0 22/6 0037:00 3.0 4.4 24.2 0018:00 1.2 22.5 0038:00 1.0 1.0 0019:00 2.1 27.0 0039:00 1.9 1.8 0040:00 2.2 7.6 24.7 0041:00 1.5 2.9 0041:30 3.0 13.8 0043:00 6.2 15.5 24.7 0047:00 2.0 2.0 0048:00 4.5 5.1 0049:00 5.0 4.1 182 1361 Table 6.5 Variation of TBsea with White Water Coverage Wavelength (cm) ATb °K A White Water \ percent 21.0 -0.068 ± 0.100 6.0 V-38° +0.102 ± 0.090 6.0H-3S' +0.047±0.030 2.8V-380 +0.135 ± 0.080 2.8H-380 +0.082 ± 0.070 1.55 +0.081 ± 0.050 0.95 +0.063 ± 0.050 0.81V -.38° +0.102 + 0.060 0.81 H-38* +0.116 + 0.060 183 1362 en Q < o 00 21 00 F - u E a LO LO LO • LO E CJ I — I 0\l • ^f LO * IrlCb vo- o oo o CM o o N c o in T3 Rl a o o CI -a o 1 o LO o «3* o 00 o CM o o o 3HhlVU3dlAI3i SS3N1H0IU9 Q3103ayO0 to CD U 3, 184 1363 190 ISO 170 160 ~ 150 cr cr UJ CL o CD 140 130 120 9 HO UJ cr cr O o 100 90 80 70 60 (^^W^) (2) (6) (3) (6) '(4) (6) ^< -(4) — -M4) (2)' •(2) 0.81 cm V 6.0 cm V .(4)/ 0.81 cm H .(4) 6.0 cm H ■(3) 10 20 30 WIND SPEED AT 155 METERS (m/s) Figure6.2. 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