H Safe Hi NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS OCEANOGRAPHIC INVESTIGATION OF THE EAST GREENLAND POLAR FRONT IN AUTUMN by William F. Perdue March 1982 Thesis Advisor: R. G. Paquette Approved for public release; distribution unlimited. T204 531 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (Wham Data Bntarad) REPORT DOCUMENTATION PAGE T reportnumbER 2. OOVT ACCESSION NO 4. TITLE (and Subtllta) Oceanographic Investigation of the East Greenland Polar Front in Autumn 7. AuTNonr«> William F. Perdue » *t*romu\MQ ORGANIZATION NAME AMO AOORESS Naval Postgraduate School Monterey, California 93940 II CONTROLLING OFFICE NAME ANO AOORESS Naval Posrgraduate School Monterey, California 93940 14 MONITORING AGENCY NAME * AOORCSBffJ dltlarant Irrnm Controlling Otltcm) READ INSTRUCTIONS BEFORE CQMPLETTNC FORM 1 RECIPIENT^ CATALOG Nu Mflf a 5. TYPE OF REDOUT a p CRlOO COVEBCO Master's Thesis M*rrh 1QP.9 • ■ PERFORMING OPG «»0»T NUMBER •• CONTRACT OP SKANT nomSCR(i) MR01541A09 PE 452-82 MR01542A09 PE 452-82 10. PROGRAM ELEMENT. phojECT task AREA * WORK UNIT NUMBERS Element: 62759N Work: 540-MH31 Project: ZF59-555 Task: ZF59-555-694 12 REPORT OATE March 1982 IS. NUMBER OF PAGES 80 IS. SECURITY CLASS, lot IKI, rapori) Unclassified ISa. OECLASSIFI CATION/ DOWN GRADING SCHEDULE IS. DISTRIBUTION STATEMENT (ol ml* 'apart) Approved for public release; distribution unlimited 17 DISTRIBUTION STATEMENT (ol tma omaltmcl mntarad In Block 30, II dltlarant tram Haport) IS. SUPPLEMENTARY NOTES Funding for this cruise and part of the analysis was provided by the Arctic Submarine Laboratory of Naval Ocean Systems Center, San Diego, California under Project Orders Nos. MR01541A09 and MR01542A09 PE 452-82, >9. KEY WOROS (Contlnum on raroraa tlda II naeaaamty *na Idmntlty ay Mac* nuPMf) Marginal Sea- Ice Zone Thermal Fine structure Greenland Sea East Greenland Polar Front Polar Front Ice Oceanography East Greenland Current Fram Strait 20. ABSTRACT (Canllnup an ravoram aid* II nacoaamrr mtd Idmntltr *T mlmek tmat) Dense data sampling, both horizontally and vertically, have provided new insight into the time/space variability of the East Greenland Polar Front during late autumn. A core of warm Atlantic intermediate Water (AIW) is frequently found pressed against the eastern edge of the front which is warmer than previously described and is often fragmented and full of finestructure. There is also finestructure present in the Polar Water in the form of lenses of anomalous water, generally warm in a cold matrix, DD FORM 1 JAN 7 J 1473 COlTiON OF I NOV «• IS OBSOLETE S/N 0 102-0 14- 6601 i UNCLASSIFIED SECURITY CLASSIFICATION OF TMIS PAOE (Whan Data tntarad) UNCLASSIFIED ftcuwty CL.*WC*TiOM Q» ▼ *«»* mmrw+m> 20. (cont.). which are formed by the turbulent entrainment of AIW at the front. There is a pronounced movement of AIW under the front which results in a warming of the waters found on the Greenland Shelf. This warm water has as its source AIW which has penetrated the lower portion of the front either some distance north of Fram Strait or along a part of the East Greenland Current or both. There is evidence that eddies or other mechanisms are involved in this process. DD Form 1473 1 Jan 73 S/N 0102-0X4-6601 UNCLASSIFIED Approved for public release; distribution unlimited Oceanographic Investigation of the East Greenland Polar Front in Autumn by William F. Perdue Lieutenant, United States Navy 3. A., University of Texas, 197a Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN METEOROLOGY AND OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL March 1982 LIBRARY ^ADUATE SCHOOL l£Y, CALIF. 93&40 ABSTRACT Dense data sampling, both horizontally and vertically, have provided new insight into the time/space variability of the East Greenland Polar Front during late autumn. A core of warm Atlantic Intermediate Water (AIW) is frequently found pressed against the eastward edge of the front which is warmer than previously described and is often fragmented and full of f inestructure. There is also f inestructure present in the Polar Water in the form of lenses of anoma- lous water, generally warm in a cold matrix, which are formed by the turbulent entrainment of AIW at the front. There is a pronounced movement of AIW under the front which results in a warming of the waters found on the Greenland Shelf. This warm water has as its source AIW which has penetrated the lower portion of the front either some dis- tance north of Fram Strait or along a part of the East Greenland Current or both. There is evidence that eddies or other mechanisms are involved in this process. TABLE OF CONTENTS I. INTRODUCTION 10 II. GENERAL OCEANOGRAPHY 13 A. BATHYMETRY 13 B. CIRCULATION 15 C. WATER MASSES 17 1. Polar Water (PW) 17 2. Atlantic Intermediate Water (AIW) 18 D. EAST GREENLAND POLAR FRONT 19 III. RESULTS 24 A. NORTHERN TEMPERATURE-SALINITY TRANSECTS .... 28 1. Transect 4 28 2. Transect 5 32 B. SOUTHERN TEMPERATURE-SALINITY TRANSECTS .... 35 1 . Transect 1 35 2. Transect 2 37 C. CENTRAL TEMPERATURE-SALINITY TRANSECTS .... 39 1. Transect 3 39 2. Transects 7 through 9 42 D. TRANSECT 6 46 IV. DISCUSSION 48 V. SUMMARY 59 APPENDIX A. INSTRUMENTATION AND DATA ACQUISITION .... 60 APPENDIX B. CTD OPERATIONS UNDER FREEZING CONDITIONS . . 64 APPENDIX C. CHARTS OF ARCTIC SOUTHERN ICE LIMIT .... 66 LIST OF REFERENCES 71 INITIAL DISTRIBUTION LIST 73 LIST OF FIGURES Figure 1. Bathymetry of the Greenland Sea 14 Figure 2. Surface circulation in the Greenland Sea. . . 16 Figure 3. Distribution of oceanographic stations. ... 25 Figure 4. Distribution of salinity-temperature transects 26 Figure 5. Distribution of salinity-temperature transects in the central area 27 Figure 6. Temperature-Salinity Transect 4 29 Figure 7. Temperature-Salinity Transect 5 33 Figure 8. Temperature-Salinity Transect 1 36 Figure 9. Temperature-Salinity Transect 2 3Q Figure 10. Temperature-Salinity Transect 3 40 Figure 11. Temperature-Salinity Transect 7 43 Figure 12. Temperature-Salinity Transect 8 44 Figure 13. Temperature-Salinity Transect 9 45 Figure 14. Temperature-Salinity Transect 6 47 Figure 15. Distribution of oceanographic stations of the icebreaker SDISTO in September 1964 and 1965. 50 Figure 16. Transect A 52 Figure 17. Transect B - Temperature (°C) 54 Figure 18. Transect 3 - Salinity (o/oo) 55 Figure 19. Transect B - Sigma-t (kg-m-3) 56 Figure 20. Southern Ice Limit Chart Legend 66 Figure 21. Figure 22. Figure 23. Figure 24. Southern ice limit - 6 and 13 October. Southern ice limit - 20 and 27 October Southern ice limit - 3 and 10 November Southern ice limit - 17 November 67 66 69 70 ACKNOWLEDGEMENT Funding for this cruise and part of the analysis was provided by the Arctic Submarine Laboratory of Naval Ocean Systems Center, San Diego, California under Project Orders Nos. MR015U1A09 and MR01542A09 PE 452-82. The author wishes to express sincere gratitude to Dr. R. G. Paguette and Dr. R. H. Eourke for their patience, support and guidence throughout the research and preparation of this thesis. Special thanks are also in order to Mike McDermet who provided helpful suggestions and support in the comple- tion of drawings and figures. Lastly, without the special support and patience of my wife, Sonja, both during my absence from home during the cruise and during the long hours of preparation, this thesis would not have been possi- ble. I. INTRODUCTION This thesis describes and analyzes some of the results of an oceanographic cruise to the marginal ice zone of the northwestern Greenland Sea in October to November of 1981 in which the author participated. The primary objectives were to: • Observe the characteristics and variability of the front along the eastern boundary of the East Greenland Current. • Search for mesoscale eddies in the frontal area. • Investigate the recirculation of Atlantic Water into the East Greenland Current. Aagaard and Coachman (1968a) list investigations in the area of interest for all seasons up to 1965 amidst a thor- ough review of the literature on the East Greenland Current. Op to the present, only three previous oceanographic cruises have occurred in the months of September to December. The first two (data were available from National Oceanographic Data Center archives) are the cruises of the icebreaker EDISTO in 1964 and 1965 which sampled with reversing bottles and used station spacings of approximately 353cm along a line. Both of these cruises took place in August and 10 September. The stations which occurred in September are indicated in Figure 15. The third cruise, by the USCGC WESTWIND in September to October of 1979, was reported by Newton and Piper (1981). The data in the latter cruise were taken by a conductivity-temperature- depth recorder (CTD) and used station spacings of about 151cm along a line. Additional information is available from the drift of the ice island Arlis II in 1964 to 1965 (Tripp and Kusunoki, 1967) ; also from several excursions of the British submarine SOVEREIGN under the ice carrying a recording sound velocimeter (Wadhams, Gill and Linden, 1979) . The present cruise was carried out with station spacings generally less than 10km in the region of the front. The Neil Brown CTD was programmed to sample about three times per meter. Thus it was possible to demonstrate the struc- ture of the waters in considerable detail, showing complex and extensive finestructure and features interpretable as eddies or meanders. There are a number of samplings of the same sections at different times, thus demonstrating the variability with time. The results presented in this thesis are based on the analysis of temperature and salinity fields. The analysis 11 of density, dynamic heights and temperature-salinity curves are left for later work. 12 II. GENERAL OCEANOGRAPHY A. BATHYMETRY Th9 bathymetry of the Greenland Sea (Figure 1) is marked by several major physiographic features. The 600km wide and 2600m deep Greenland-Spitsbergen passage, known as Fram Strait, forms the principal route for water exchange between the Arctic Ocean and the rest of the world ocean. A broad continental shelf extends southward along the east coast of Greenland with the shelf break at approximately the 400m isobath. In the region of Belgica Bank, the shelf reaches its widest extent of approximately 300km and' then narrows rapidly to less than 100km at about 75°N. The shelf is marked by several depressions and a system of banks less than 200m in depth. The largest depression, Belgica Dyb, has a depth in excess of 400m. A system of prominent ridges serves to define the limits of the Greenland Sea and divide it into two major basins. Extending from Greenland eastward to Jan Mayen at about 71°N, the Jan Mayen Fracture Zone forms a sill of the order of 1500m in depth and marks the southern extent of the 13 ^ 20°W 82°N _ 15 15°E 82°N Figure 1. Bathymetry of the Greenland Sea. Adapted from the chart of Perry, Fleming, Cherkis, Feden am Vogt (1980). Bottom contours are in 100«s of meters. 14 Greenland Sea. From Jan Mayen, a portion of the Mid- Atlantic Ridge known as the Mohn Ridge extends northeastward toward Spitsbergen. This ridge forms the logical oceano- graphic boundary between the eastern limit of the Greenland Sea and the Norwegian Sea -co the south and east. The third important ridge lies northwest/southeast between Greenland and the Mohn Ridge from about 77°N, 5°W to 74°N, 5°E and separates the two basins of the Greenland Sea. The southern basin is the larger and deeper of the two, with depths of approximately 3800m. The northern basin is about 3200m in depth. B. CIRCULATION The surface circulation in the Greenland Sea is shown in Figure 2. The circulation is derived from a map given by Aagaard and Coachman (1968a). Added have been possible routes for the recirculation westward into the East Green- land Current of approximately 30 x 10* m3s-* of the water from the West Spitsbergen Current mentioned by the same authors. Also added is the western branch of the Norwegian- Atlantic Current along the Iceland-Jan Mayen Ridge inferred by Carmack and Aagaard (1973) . 15 20°W 82°N _ 15 Figure 2. Surface circulation in the Greenland Sea. 16 C. WATER MASSES Three water masses have been recognized historically within the East Greenland Current north of the Denmark Strait and in the Greenland Sea. Aagaard and Coachman (1968a) identified these as the Polar Water flowing out of the Arctic Ocean, the Atlantic Intermediate Water found in the eastern limits of the current, and the Deep Water which represents the majority of the water found in the Greenland Sea. More recently, Swift and Aagaard (1981) expanded and modified the water mass terminology of the Greenland and Iceland Seas. In the area cf the present study, their clas- sification unnecessarily complicates the descriptions and the older nomenclature has been preferred here. Only Polar Water and Atlantic Intermediate Water are discussed below as Deep Water is generally associated with depths in excess of 800m and was seldom sampled during this cruise. 1. Polar Water (PW) Polar Water is primarily confined to the continental margin of the Greenland coast and extends from the surface to a depth of approximately 150m. Originating in the Arctic 17 Ocean, PW flows out through the Greenland-Spitsbergen pas- sage as part of the East Greenland Current. PW is charac- terized by low temperatures and low salinities. The temperatures vary from near freezing at the surface to 0°C at the bottom of the layer while the salinities form a strong halocline with values of 30.0 o/oo or less near the surface and a maximum value of 34.5 o/oo (Aagaard and Coachman, 1968a) . 2. Atlantic Intermediate Water {AIW) Atlantic Intermediate Water is a relatively warm, saline water water mass which is found east of the front. As defined by Aagaard and Coachman (1968a), the temperature of AIW is always greater that 0°C, with a temperature maxi- mum normally present lying between 200 and 400m. The salin- ity of AIW has been defined as characteristically greater than 34.88 o/oo by the same authors. On the western side of the front, there is a warm water mass with properties similar to AIW. The temperatures are greater than 0°C. However, the salinities of 34.5 o/oo to 34.9 o/oo appear to have somehow been diluted from the properties given above for AIW. Therefore, this water rep- resents AIW which has mixed with cooler, usually less saline 18 water such as PW. It is possible that this mixing has taken place in or north of Fram Strait or it may have occurred along the front. D. EAST GREENLAND POLAE FEONT Past studies have frequently referred to the front formed by the East Greenland Current as the Polar Front. Another front, also termed the Polar Front, exists along the eastern boundary of the Greenland Sea overlying the Mohn Eidge and another to the south and east of Spitsbergen, In order to distinguish between these fronts and to provide a more descriptive name, the terminology introduced by Wad- hams, Gill, and Linden (1979) will be adopted and the more westerly of these fronts will be refered to as the East Greenland Polar Front. The East Greenland Polar Front marks the eastern edge of the East Greenland Current, separating the cold, relatively fresh polar water flowing southward out of the Arctic Ocean from the wa|rm, saline waters of Atlantic origin to the east. The front forms a boundary in which the isotherms, isoha- lines and isopycnals slope westward with depth to depths cf about 200m or more. Aagaard and Coachman (1968b) arbitrar- ily chose the 0°C isotherm and 34.5 o/oo isohaline at 50m 19 depth to mark the eastern limit of the front near the sur- face. In the descriptions below, the surface position cf the front has been found by following the closely packed isotherms and isohalines as they approach the surface and extrapolating, if necessary. Where frontal slopes are given numerical values, it is the slopes of isotherms which are singled out. There has been considerable variability in reports of the slope of the front. Aagaard and Coachman (1968b) reported a slope downward to the west exceeding Im-km-1 over 120km or more at latitude 75°N. Based upon submarine cross- ings of the front between depths of 85 and 122m and at lati- tude 80°-30»N, wadhams et al. (1979) calculated a slightly smaller slope of the order of 1 in 1200. Values reported by Newton and Piper (1981) show a much steeper slope of 3.3m-km-1 in the region of Belgica Dyb. Such variations in slcpe is not unexpected and can be due to differences in either position or time, as will be seen later. Values for the slope of the front from the present cruise varied from 1.5m-km-i to 20m-km-*. A significant feature which has been associated with the East Greenland Polar Front is the existence of subsurface 20 cores of relatively cold water east of the front. Aagaard and Coachman (1968b) discussed three such cold patches found near the front at about 75°N, 78°N and 79°N between 30m and 75m in depth. The temperatures were less than 0°C and salinities were between 34.0 o/oo and 34.6 o/oo. They did not demonstrate that the apparent density anomaly persisted in spite of the corresponding salinity changes. Several explanations for the possible causes of such features were suggested by the same authors. These included detached eddies, quasi-stationary meanders and variations in the intensity of the Greenland Sea circulation. Newton and Piper (1981) found another cold core near 79°N only a few miles from one of the cores discussed by Aagaard and Coachman (1968b). It is interesting that simi- lar eddy-like structures have been reported in the same gen- eral area in the past. Gladfelter (1964) found one by temperature and salinity measurements; Vinje (1978) found one using buoy drifts and satellite imagery. Vinje (1978) also indicated that this eddy might be a semi-permanent, bottom steered eddy due to the presence of a circular depression (Molloy Deep) centered at 79°15,N, 3°E. This deep is about 2000m deeper than the surrounding bottom 21 topography and about 60km in diameter. Wadhams et al. (1979) suggested that it is not clear whether all the eddies found in this area are really the same eddy, or whether the front in this region is simply a fertile generator of eddies. Another phenomenon which may contribute to the formation of the cold core structures may be associated with the local variability in the position of the East Greenland Polar Front. Aagaard and Coachman (1968b) noted several examples of apparent lateral movement occurring within relatively short time periods. One case cited a movement of the order of 100km within a few days. Although they did not clarify the mechanism, they suggested that such a movement could leave behind cold patches of water to the east of the front or contribute to the formation of eddies. Warm eddies also have been inferred in and west of the frontal zone by Wadhams et al. (1979). They interpreted f luctuatuions in sound velocity profiles found during tran- sects through the front by a submarine at depths of 67 and 85m as warm regions. One final phenomenon which may have some importance in relation to the Bast Greenland Polar Front is the indication 22 of temporal variation in intensity of the flow of Polar Water (Aagaard and Coachman, 1968b) . In previous data, pul- sations in ice drift velocity of one to two week period have been noted, probably reflecting similar pulsations in the water flow. From current measurements taken during the drift of the ice island Arlis II in the East Greenland Cur- rent in 1965, there are indications that relatively large variations in the flow may cccur over time periods as short as a day (Tripp and Kusunoki, 1 967) . Pulsations in either the ice or the water velocity might be expected to cause variations in the nature of the front. 23 III. RESULTS The position of the front, both its near-surface and most deeply submerged manifestations, and the varying pos- ticns of the ice edge are shown in relation to the station array in Figure 3. The ice edge shown in the figure is not synoptic, having been constructed from observations of the position of the ice taken at the time of each ice margin crossing and from helocopter observations near 75°N. Addi- tional information concerning ice conditions at the time of the cruise is provided by weekly southern ice limit charts produced by the Naval Polar Oceanographic Center (NPOC) (Appendix C) . The location of the front depicted in Figure 3 was determined from nine temperature and salinity transects con- structed from data acquired during the cruise. The transects are numbered in chronological order and indicated in Figure 4 and Figure 5 by the solid lines connecting stations. The nature of the frontal region varies in complexity according to geographic area. A relatively simple structure 24 82 N Figure 3. Distribution of oceanographic stations. The position of the ice edge is shown as veil as the deep (broken line) and shallow (solid line) lanifestatons of the front. 25 82 N Figure 4. Distribution of salinity-temperature transects. Locations of transects are indicated by the solid lines connecting stations. The central portion of the study area (indicated by the box) is expanded in Pigure 5. 26 76*15 N Figure 5. Distribution of salinity-temperature transects in the central area. Locations of transects are indicated by the solid lines connecting stations. 27 is seen in the northern transects, becoming somewhat more complex in the southern transects and very complex in the center of the study area. For this reason, the transects will be presented in that order. Transect 6 represents a short transect in which only a small portion of the front was crossed. Because of this and several unusual features noted in the region, this transect will be presented separately. A. NORTHERN TEMPERATURE-SALINITY TRANSECTS The northern temperature-salinity transects were obtained near 78°N. These are Transects 4 and 5 of Fig- ure 4 . 1 . Transect 4 Transect 4 (Figure 6) was constructed from data acquired from stations 50 through 62 while inbound onto the Greenland continental shelf. The stations were occupied over a 39 hour period and are therefore thought to be rea- sonably synoptic. XBT profiles 90, 91 and 95 were added to the transect in the region of the front in order to provide a more complete picture of the frontal structure near the surface. 28 Q> M <0 3 .n OS T3 1) £3 -C TJ •M *— >^ -Q » T30 0) o> -P rt oi U 3 •H O T3-H £3 P H c/1 U (3 • 01 01 a o> W £3 0>-H j3^ P O £3 oi a> H^ 0 M ..a 3- 0> •PJ3 u-p (D 01 >» £3.Q 0 U 0} H a> £3 >rH pH •H rtl £3-C •H O r-» 01 «J'H VI 1 »• a> o) M a> . 3 £3 01 *j-na idHO U f-l 0)T3«a o^h 3HEh (V OCQ E-t 01M u fe 29 The East Greenland Polar Front appears as an intense temperature front coincident with a strong salinity front lying between Stations 50 and 53. The isopieths of tempera- ture and salinity slope steeply downward (4. 8m- Jem-1) from near the surface to about 200m depth then turn sharply toward the bottom of the continental slope. The 27.6 kg-m~3 siqma-t surface, approximately in the middle of the sharpest horizontal gradient., slopes slightly less steeply and levels off at about 160m depth. This general characteristic of the isopycnals as compared to isotherms holds also in the other frontal transects described below. The lower portion of the front is close to the shelf break. This relationship is seen in other transects of the present cruise as well as in the historical data. To the east of the front below 100m lies a large region of water which meets the definition of Atlantic Intermediate Water. A well defined core within the AIW with maximum temperature >3.0°C is present between 100 and 500m depth and between Stations 50 to 53. This core and associ- ated water may represent a portion of the return flow of Atlantic waters discussed by Coachman and Aagaard (1974) and will be seen in other transects from the present cruise. 30 West of the front, a wedge shaped layer of Polar Water can be identified. Extending from the surface to approximately 180ra, a strong halocline is evident with salinities increasing from <31.0 o/oo at the surface to about 34.5 o/oo in the region of the 0°C isotherm. Temperatures vary from 0°C at the bottom of the layer to values near freezing (<-1.7°C) near the surface. Numerous parcels of anomalously warm or ccld water form temperature inversions and finestructure in the lower part of the PW. Below the 0°C isotherm, temperatures rise slightly to ♦0.5°C at the bottom. These temperatures coupled with salinities of 34.6 o/oo to >34.8 o/oo, indicate diluted AIW. The nature of the front near the surface can be related to some degree to the advance or retreat of the ice margin. In this transect, the ice edge lies between XBT profiles 90 and 91, about 151cm seaward of the shallow por- tion of the front. The isopleths of temperature and salin- ity appear to have been stretched eastward, creating a gentler slope in the front near the surface. This could be caused by an advance of the ice edge eastward with conse- quent cooling of near-surface water. That such an extension of the ice edge did occur may be seen from ice-limit charts 31 produced by the Naval Polar Oceanographic Center (Figures 21 and 22, Appendix C) . An advance in the ice margin of about 35km in the two week period from 13 to 27 Octccer 1981 occurred near 78°N. 2. Transect 5 Data acquired from stations occupied in the transect lying just north of Transect 4 were used to construct Tran- sect 5 (Figure 7) . Although the stations were occupied over a period of 5 days, the stations in the region of the front were occupied over a 15 hour period and may be regarded as synoptic. Stations 74 through 78 represent the region of the front about 10.5 days later than that seen in Tran- sect 4. Again the front appears as an intense and steep temperature-salinity front with isopleths sloping downward toward the shelf at about 3.8m-km-1. The ice edge in this transect was located between Stations 77 and 78, coincident with the shallow portion of the front. The slope of the front near the surface becomes gentler and displays the same eastward stretching of the isopleths seen in the previous transect. The ice margin in this case had advanced another 35km from 27 October to 10 November. 32 0} (d M J3 -P O tfl -M y 0) 01 - » M •HH •H H a (d-H en i to y id M 3>d ■p a) id +> u id 0) u QT3 CV C 0) M 5 (*i«t*ui)Hid3a 33 A notable contrast between this and the previously discussed representation of the front is in the warm core in the AIW east of the front. In 10.5 days, the structure of the core altered considerably. Instead of being a single well-defined core, the AIW is distributed among several cores or parcels extending from about 50m in depth to 500ra or more. The maximum temperature anywhere in the region of the AIW is near 2.5°C, 0.5°C cooler than in the earlier transect and the maximum salinity is slightly higher, 35.03 o/oo versus 34.96 o/oo. This probably is a region of turbulent mixing, a condition which seems to be common along the front. Perhaps included in the same turbulent process is the parcel of warm water near Station 73 and 200m depth, to the west of the front. This suggests a tendency for AIW to mix across the front in large parcels at depths of about 200m. Similar behaviors will be seen in more southerly transects. The PW in this transect is similar in properties and thickness to that in Transect 4. The diluted AIW found below the 0°C isotherm also is similar except for the warm parcel at Station 73 mentioned above. 34 B. SOUTHERN TEMPERATORE-S ALINITY TRANSECTS The southern temperature-salinity transects represent transects of the front obtained, in the region of Belgica Dyb. These are Transects 1 and 2 of Figure 4. 1 . Transect 1 Transect 1 (Figure 8) represents the most southerly transect of the East Greenland Polar Front during the cruise. The stations were occupied over a 62 hour period while inbound on the shelf in the region of Belgica Dyb. The temperature front in this transect is the most intense seen during the cruise. The isotherms slope very steeply down from the surface to about 150m with a slope of about 20m-km-1. In this case, the isohalines slope much less steeply. The bottom portion of the front appears to overlie the region of the shelf break as in previous transects. Again one sees the Atlantic Intermediate Water bro- ken up into secondary cores or parcels. The tendency of the AIW to penetrate the lower portion of the front is more pro- nounced than in Transect 5. A large parcel of warm, undi- luted AIW is found at Station 11 and 200m depth near the base of the front. Additionally, warm, undiluted AIW can be seen along the surface of the shelf and a particularly warm, 35 o M M id ■pv U VI a> (Q G • flJvO Ul H 0) M >»fl -P D> •Ht-» C£m •H ^ a (0«H en 1 w (1) (0 M ST3 ■M d> (0-M M «J (V u CUH a a H'H (sj«t*uitHid3a u 36 essentially unaltered parcel is visible as far as in Station 20. This represents a well-defined intrusion of the AIW across or below the front. This penetration of AIW landward is more pronounced than in Transect 4 possibly because of the flow of water into Belgica Dyb proposed by Newton and Piper (1981) . 2. Transect 2 Cross section 2 (Figure 9) was constructed from data obtained while headed eastward from Belgica Dyb. Again the data are considered to be approximately synoptic, having been acquired over a 24 hour period. This transect provides a representation of the East Greenland Polar Front eight days after that of Transect 1. The front remains clearly defined. It is less intense than in Transect 1 and less steep, with a slope of approximately 8.5m-km-1, as compared to the slope of 20m-km-1 eight days previously. The bottom of the front extends to about 200m depth, approximately 50m deeper than Transect 1. Additionally, the lower portion of the front overlies the upper continental slope as before. There is some evidence of the flattening of the front near the sur- face which has been associated with the advance of the ice 37 STO NO. 47 31 32 100 200 - 300 400 500 ■343%. 34.9%. M 40 50 DISTANCED m) Figure 9. Tenperatu re- Salinity Transect 2. Isotherms and isohalines are indicated as in Figure 6. Station 47 was an XBT drop. 38 margin in previous discussions. However, the ice edge is found near Station 30 in this case, which is behind the sur- face manifestation of the front. A possible explanation for this may be an advance in the ice margin which subsequently retreats and leaves a layer of PW to the east. From the ice charts in Appendix C, it appears that such an event may have occurred. From 13 to 20 October, the ice edge in the region of Transect No. 2 (near 76°-3Q,N) grew about 10km eastward. The chart of 27 October shows the ice margin to have returned westward to the position of 13 October. C. CENTRAL TEMPERATURE-SALINITY TRANSECTS Transects 3 and 7-9 represent transects through the central part of the study area (Figure 5) and provide an interesting view of the variability of the front over small scales of time and space. 1 . Transect 3 The transect represented by Transect 3 (Figure 10) was completed relatively early in the cruise on 26 October during a 14 hour period. Its western end is about 35km sea- ward of the shelf break, which prevents seeing the way in which the front approaches the shelf. Station spacings were somewhat larger than in the other transects (15-20km) and some of the fine detail seen elsewhere may have been missed. 39 349%. 34.9%. 30 40 50 OISTANCE(km) Figure 10. Temperature- Salinity Transect 3. Isotherms and isohalines are indicated as in Figure 6. 40 There is a relatively sharp slope in the isopleths of about 5 . 2 m — k m— *• between Stations 37 and 38. The near- surface portion of the front stretches eastward, similar to what has been seen in other transects. The ice edge was located near Station 39 and had advanced about 25km ever a period from 20 to 27 October. As seen from earlier discus- sion, this advance may be responsible for the apparent spreading of the front to the east. Additionally, the front flattens out abruptly at 100m depth and extends westward from station 37. This may be a breaching of the lower por- tion of the front as occurred in Figures 8 and 9. However, the unusually shallow depth at which this occurs and the general downward trend of the deeper isotherms near Sta- tion 36 suggest that a deeper manifestation of the front may have existed further to the west. Just east of the front, but considerably shallower than before, the characteristic warm core of AIW is seen with the maximum temperature now reduced to about 2°C. Below the front, temperatures remain above 0°C, also corre- sponding to AIW, except for a small region below 400m between Stations 38 to 40 which is, by definition, Greenland Sea Deep Water. Salinities in the western part of the 41 transect are slightly lower than the values defined for AIM. However, one large area in the eastern part with salinities greater than 34.9 o/oo and a smaller area at Station 36 gualify as AIW. 2. Transects 7 through 9 Transects 7, 8 and 9 (Figures 11, 12 and 13) repre- sent three transects of the East Greenland Polar Front accomplished over a period of less than four days from 11-15 November. It is particularly interesting to note the close proximity of Cross Transects 7 and 9 (Figure 5). Stations 99 and 107, and Stations 94 and 113 should be superimposed in comparing the two transects. The slope of the front in all three transects is relatively gentle with values ranging from 1.5m-km~l to 2.3m-km~l. Again, one sees the eastward spreading of the near surface portion of the front which appears to be asso- ciated with the 40km advance of the ice margin in this region from 26 October to 15 November (Figure 3) . The deep end of the front is not present in any of the three transects. Perhaps the most striking differences noted in Tran- sects 7 through 9 is in the variability of the Atlantic 42 STA NO. 0 100 - 200 - 300 400 500 \ 3* H 10 20 30 ♦O 50 DISTANCE (KM) 70 80 90 Figure 11. Temperature-Salinity Transect 7. Isotherms and isohalines are indicated as in Figure 6. 43 20 30 DISTANCE (km) Figure 12. Tenperature-Salinity Transect 8. Isotherms and isonalines are indicated as in Figure 6. 44 STA. NO. 0 113 119 120 100 - 200 300 400 500 33.0%. 33.5%. 34 0%. 34.5%. 34.7%. 348%. 34.9%. 39.0%. W 10 20 DISTANCE (Urn I Figure 13. Tenperature-Salinity Transect 9. Isotherms and isohalines are indicated as in Figure 6. 45 Intermediate Water. In Transect 7, the warm AIW east cf the frcnt contains much f inestructure suggesting turbulent mix- ing of an intensity not previously seen. In contrast, Tran- sect 9, only 3.5 days later than Transect 7, has a well defined core of warm AIW, scarely fragmented at all. Like- wise, Transect 8f displaced only a short distance southward, shows little fragmentation in the AIW. D. TRANSECT 6 Transect 6 (Figure 14) represents the most northerly transect accomplished during the cruise. Due to the rela- tively short distance covered by this transect, the crossing of the East Greenland Polar Front was not completed. Evi- dently, the transect is near the eastern (surface) end cf the front and a thin layer of Polar Water extends eastward beyond Station 79, probably as a result of an 80km advance in the ice margin from 3 to 10 November. AIM is present in nearly all the volume beneath the PW. There is also an intervening thin layer of diluted AIW. AIW extends to 500m depth and more. Particularly notable is the prominent dome in the isotherms at Station 81 suggesting a submerged cold- core eddy. 46 STA NO. 0 100 - 200 - 300 - 400 " SOO <33.%. W 20 30 DISTANCE < km) 50 Figure 14. Tea perat tire-Salinity Transect 6. Isotherms and isohalines are indicated as in Figure 6. 47 IV. DISCUSSION We have seen the northern portion of the East Greenland Polar Front as a sharp, steep boundary between warm, saline Atlantic Intermediate Water on the east and cold, more dilute Polar Water underlain by a cooled layer of slightly diluted AIW on the west. The front consistently lies over the upper continental slope. Selatively warm AIW is close against the front in the depth range 200 to 400m. This warm water appears to be concentrated here in one core or a num- ber of smaller filaments or parcels. However, there may be a continuity of the warm parts of this water with similar water to the east. The high temperatures and high salinities found in the AIW adjacent to the front are indicative of a relatively direct connection with the Atlantic waters in the West Spitsbergen Current. There can be little doubt that this water is part of the recirculating water from the West Spitsbergen Current mentioned by Coachman and Aagaard (1974). It would be interesting to know if the warm AIW observed during this cruise has come more or less directly 48 from the east or if it was injected at a more northerly point and flowed southward along the front. In two tran- sects (Figures 6 and 8) , there seems to be no well-defined continuity of the warmest AIM to the east. In other tran- sects, the lack of continuity is not demonstrated, particu- larly if one conceives of the water arriving in the form of parcels or filaments which give the appearance of discontin- uity. However, in all transects of the present cruise, AIM of intermediate temperature obviously continues eastward, to what distance it cannot be determined. Thus, the question of the more or less direct flow of warm AIM from the east cannot be answered with the present data. Some insight into conditions farther to the east than the limits of the present survey may be had from the EDISTO data. The positons of two sets of temperature, salinity and density transects are indicated by the solid lines connect- ing stations in Figure 15. In Transect A (Figures 16) temperatures of greater than 3°C are seen at the surface, but they are too dilute for AIM. Below approximately 90m, temperatures up to above 1.5°C have salinities high enough to be called AIM. The AIM with this degree of warmth is located against the front, 49 82 N Figure 15. Distribution of oceanographic stations of the icebreaker EDISTO in September 1964 and 1965. Locations of transects are indicated by the solid lines connecting stations. 50 typically like the corresponding waters in 1981. Although this data is from September, the maximum temperatures are lower than 1981. The lower temperature in this year may be due to year-to-year variation. The transect extends only as far eastward as Transects 1 and 2 and therefore, does not provide much insight into conditions to the east. The maxi- mum temperatures lie along isopycnals 27.9-28.0, which rise rapidly toward the east. This suggests a continuity with water farther to the east near or at the surface. Transect B (Figures 17-19) extends approximately 60km farther eastward than Transect 6. Temperatures in the .AIW are similar to the values seen in the present data. In con- trast to Transect A, the warmth in the AIW (salinity > 34.88 o/oo) does not appear to extend to the surface, but is held deeper than about 100m by a superficial layer of decreased density. The parcel of water warmer than 2.5°C on the right near 100m depth is approximately on the 35.0 o/oo isohaline. Temperatures decrease with depth to 500m but all of the deeper water to the east of the 275km mark may be classified as AIW. This extension of warm AIW to the east suggests that there is a continuous supply of this water from that direction. The previously mentioned parcel of 51 a < 2 g 55 !W)Hid3Q a •H O O o > z -I < (MlHidBQ •H •H G •H <0 en o M V id M a* a 0) a U (Ml Hld3Q 52 water >2.5°C in the eastern portion of the transect suggests that the warmest AIW may arrive as parcels or filaments carried in the westward flow. Other warm parcels may have been missed by the large station spacings, approximately 60km. In the present data, the finestructure visible in the Polar Water layer west of the front is less pronounced than in the AIW. Wadhams, Gill, and Linden (1979) also observed that the amplitudes of the fluctuations in sound velocity transects were greater on the warm side of the front in the AIW. The majority of the finestructure in the PW is made up of warm-in-cold parcels of the order of 15m in thickness and 10km in diameter. These may be seen in Figures 6, 8 and 9 lying bove approximately 130m depth. The fact that they are mostly warm-in-cold suggests that the parcels are propagat- ing from the warm frontal zone. Since this is a region of high velocity shear, it is likely that these parcels have at some point been torn out cf the frontal zone by shear-in- duced turbulence. This same mechanism may account for some of the fragmentation seen in the AIW near the front. Large concentrated parcels of AIW are found upon the shelf and propagating shoreward beneath the front 53 a Hi CC D < OC LU a 2 at o M •M <0 M 0) a* a z -J < CO o o \ o •p •H a •H *H it» CO -p O CD CO a, <• o»»»4»i In caacantrotiaat '•«• ittaa ••• i«ik. ICf-ftEt Na ••• ic» Ic» •• law* .«».« (.taaa»t t. «.) Mf b. »r...m IP TH1CKN«S (API) 010 '■»»*»*•• bci* *vi*-v«ai ana i»c»n«-T«« •<•• G»««raily 2 • 3.J * thick. FY A«v a» ait fern r««» ica typ«t (30 ca> • 2 • ihick). TNO Tavaa ica (10 - 10 cat thick). N N*a •■• ••*•».. H f ••* '**• '•• ■** »",«* '•»■• •"* r«a*m <•»• alaag lha tc««« 121 Thaatattca* Ihtcknacc at thi» laaaaa'i j.«»ik (cat. »a>*« an (taatiaa, 4»v aaT» (afaaaataa1 (at tirtt day ai ••<> aania •« licit ivccaadiaa chart) lea aa»aaa«T »»M»aU» at lotatUca aaaatvatl. ■ ». / "^*- • / ^"^ Ip^u/ ' / x<5Tr"~'-jL / '~i^\\\jvli Ih»9b*^ M 0) ^3 O -P CJ O r* a o r>4 ■r-» a •H a> o •H (3 M o 3 T3 (3 (0 en I a 0) U •H a u 0) -3 •P o CO 0) u 3 a* 69 Figure 21. Southern ice liait - 17 November 70 LIST OF REFERENCES Aagaard, K. , Wind-driven transports in the Greenland and Norwegian seas, Deep Sea Res. ,17, 281-291,1970. Aagaard, K. , and L.K. Coachman, The East Greenland Current north of the Denmark Strait, I, Arctic. 21 13) , 18 1-200, 1968a. Aagaard, K. , and L.K. Coachman, The East Greenland Current north of the Denmark Strait, II, Arctic, 21 (4) . 267-290, 1968b. Bourke, R.H., and R.G. Paquette, Winter conditions in the Bering Sea, Tech. Rep. NPS 68-81-004, Dept. of Oceanography, Naval Postgraduate School, Monterey, Calif., 1981. Carmack, E. , and K. Aagaard, On the deep water of the Greenland Sea, Deep Sea Res., 20, 687-715, 1973. Coachman, L.K., and K. Aagaard, Physical oceanography of arctic and subarctic seas, in Marine Geology and Oceanography of the Arctic Seas"! chap. 1 , pp. 1-/2 , Springer, New York, 1974. Gladfelter, W.H., Oceanography of the Greenland Sea, (JSS ATKA JAGB-3) survey, summer 1962, Informal manuscript report 0-64-63, U.S. Naval Oceanographic Office, Washington D.C. , 154pp., 1964. Newton, J.L. , and L.E. Piper, Oceanographic data from northwest Greenland Sea: Arctic Easr 1979 survey of the USCGC WESTWIND, Rep. SAI- 202-8 1-003-LJ, Science Applications, Inc., La Jolla, Calif., 1981. Perry, R.K., H. S. Fleming, N.Z. Cherkis, R.H. Feden, and P.R. Vogt, Bathymetry of the Norwegian-Greenland and West Barrents seas, U.S. Naval Research Laboratory - Acoustics Division, Environmental Sciences Group, Williams and Hein Map Corporation, Washington D.C, 1980. Swift, J.H.f and K. Aagaard, Seasonal transitions and water mass formation in the Iceland and Greenland seas, Deep Sea Res., 28A(10) , 1107-1129, 1981. Tripp, R.B., and K. Kusunoki, Physical, chemical, and current data from Arlis II: Eastern Arctic Ocean. Greenland Sea, and Denmark Strait area. February 1964-May 1965, University of Washington Dept. of Oceanography, Tech. Rep. No. 185, 1967. Vinje, T. , On the use of data bouys in sea ice studies, paper presented at WMO Workshop on Remote Sensing of Sea Ice. World Meteorol. Organ., Washington D.C, Oct. 16-20, 1978. 71 Wadhams, P. , The ice cover in the Greenland and Norwegian seas. Reviews of Geophysics and Space Physics, 19 13) . 345-593, iyy i . Wadhams, P., A. E. Gill, and P.F. 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Perdue, USN Naval Eastern Oceanographic Naval Air Station Norfolk, Virginia 23511 Center 80 Thesis 1 QQ1 /, fl o P3346 Perdue "*U 3 c-1 Oceanographic inves- tigation of the east Greenland polar front ant in autumn. res- it 2S0CT83 aa i *».•■* )U 5 OCT 9? £lP£ff l 5 OCT 9? 0045] Thesis J SSI ^0 P3346 Perdue c.l Oceanographic inves- tigation of the east Greenland polar front in autumn. Mm