AN ATLAS OF SECCHI DISC TRANSPARENCY MEASUREMENTS AND FOREL-ULE COLOR CODES FOR THE OCEANS OF THE WORLD By Margaret Anne Frederick DUDLEY KNOX LIBRARY NAVAL 7 0STGRADUATE SCHOOL MONTEREY. CALIFORNIA 93943 ^ ■ K . United SI tes Pc rsiou-' 3 . ~r-'- .-- b V=^ V»^ is L J~ . ±j !::2; . 1 AN ATLAS OF SECCHI DISC TRANSPARENCY MEASUREMENTS AND FOREL-ULE COLOR CODES FOR THE OCEANS OF THE WORLD t>y Margaret Anne Frederick September 1970 TkU dociumnt hcu bum a]ip.>wve.d Ion. pubtlc. 'it- ttcL&e. and 4&£e; JUj> dl&&u,b- ill ............................■'■'0 INITIAL DISTRIBUTION LIST 180 FORM DD 1473 . . ................. 187 LIST OF TABLES TABLE I. Vertical Extinction Coefficients and Their Reciprocals Computed from Secchi Disc Depths 169 II. For3l-Ule Color Scale, Proportions of Component Chemical Solutions and Color Shades 170 IIIo Monthly Minimum and Maximum Transparency and Color Code Values for the Sea of Japan 171 LIST OF FIGURES FIGURE 1A Secchi Disc Transparency Observations Between 100 E and 90 W Longitude . . . . .... 64 IB Secchi Disc Transparency Observations Between 100 /J and 100 E Longitude . . , „ . 65 2A Forel-Ule Color Code Observations Between 100 5 and 90 V.7 Longitude 66 2B Forel-Ule Color Code Observations Between 100 J and 100 E Longitude 67 3-4 Transparency and Color Code Contours for the Bering Sea , 68-69 5-6 Transparency and Color Code Contours for the Sea of Okhotsk . 70-71 7-19 Transparency Contours for the Sea of Japan . . . „ . . 72-84 20-32 Color Code Contours for the Sea o:3 Japan „ 85-97 33-45 Mean Transparency Deviations for the Sea of Japan . . . 9S-110 46-58 Mean Color Code Deviations for the Sea of Japan .... 111-122 59-60 Transparency and Color Code Contours for the Yellow and East China Seas 124-12! 61-62 Transparency and Color Code Contours for tlic Gulf of Tonkin 126-127 63-64 Transparency and Color Code Contours for the South China Sea and the Gulf of Thailand . „ . . » . o 128-129 65 Transparency Contours for the Gulf of Alaska 130 66A Transparency Contours for the North Facific Ocean Between 110 E and 170 W Longitude 131 66B Transparency Contours for the North Pacific Ocean Between 170 E and 100 W Longitude .132 67A Color Code Contours for the North Pacific Ocean Between 100 E and 170 W Longitude . „ » . 133 67B Color Code Contours for the North Pacific Ocean Between 170 E and 100 W Longitude 134 7 68 Transparency Contours for the Eastern South Pacific Ocean . . . 135 69 Color Code Contours for the North Atlantic Ocean . . . 136 70-71 Transparency and Color Code Contours for the Caribbean Sea , 137-138 72 Transparency Contours for the East Siberian> Chukchi and Beaufort Seas 139 73-74 Transparency Contours for the Barents and the Kara Seas 140-141 75 Transparency Contours for the Blsck Sea . 142 76-77 Transparency Contours for the Western and Eastern Basins of the Mediterranean Sea . 143-144 78-79 Color Code Contours for the Western and Eastern Basins of the Mediterranean Sea 145-146 80-81 Transparency and Color Code Contours for the Summer Monsoon Season for the Indian Ocean 147-148 82-83 Transparency and Color Code Contours for the Winter Monsoon Season for the Indian Ocean 149-130 84-85 Transparency and Color Code Contours for the Southern Ocean 151-152 86 Transparency Contours for the Ross Sea . 153 87-91 Scatter Diagrams of Secchi Depths vs. Forel-Ule Color Codes * 154-158 ACKNOWLEDGEMENTS I would like to express my appreciation to my thesis advisor, Assistant Professor Robert S. Andrews, Department of Oceanography, and to Department Oceanographer Stevens P. Tucker, under whose direct supervision the data analyses were initiated when he was an assistant professor (1968-70). Mr. Tucker's enthusiasm for this project and his assistance, particularly in providing reference material, greatly aidec in the completion of the project I am also indebted to Mr. Henry Oduai of the National Oceanographic Data Center for providing the data tape. The assistance of the Postgraduate School library staff and Mr. Alan Baldridge of Hopkins Marine Station in locating and making available reference material is greatly appreciated. I would also like to thank Miss Sharon D. Raney of the computer facility for her assistance in adapting the data tape for use on the Postgraduate School computer. Lastly, I would like to thank Mr. Robert Owen for his composite transparency charts and Dr. Robert R. Dickson for his kind permission to include his transparency chart for the North Atlantic Ocean in this work. 10 I. INTRODUCTION A. GENERAL Although sea water has an optical character as well as biological and chemical characters the properties which constitute its optical character have not been examined as extensively as other oceanographic parameters. Nevertheless a knowledge of optical conditions in the sea has a number cf applications, suggesting that detailed investigations are desirable. Fcr example, photosynthetic activity in the ocsan is a function of light in- tensity, and studies of the effect of light intensity on photosynthetic rates of plarkton are necessary in investigations of primary productivity. Also, the ecological niches occupied by biological organisms involve mary factors, including light levels, the wavelength, and the polarisation oi the ambient light, field. It has been noted by Uda (44) that transparency measurements are often useful in corroborating the productivity indicated by the relative values of the dissolved oxygen content found in the. upper layers of the ocean. The transparency of sea water is also related to the abundance of plankton present in the surface layers of the sea and can provide at least a quali- tative measure of the geographical distribution of planktonic life. The color of sea water can sometimes be used as a measure of the abundance of planktonic organisms. Jerlov (22) and others have suggested that optical data may be used in various ways to obtain useful information about oceanographic conditions since the optical properties of the water are dependent on the physical, chemical, and dynamical conditions of the sea, and the distribution of opti- cal parameters may be useful in the characterization of water masses. 11 Although optical measurements are by no means numerous on a world wide basis, a compilation of available data is a useful starting point in the examina- tion of the optical "structure" of the world's oceans. On a global basis, the optical properties of sea water that have been examined and measured most extensively are transparency and color, as deter- mined by use of the Secchi disc and the Forel-Ule color scale, or some modification of these. It is recognized that both determinations are at their best only semi-quantitative. Nevertheless, despite their short- comings as precise quantitative descriptions of optical conditions, such measurements represent the only available indication of the optical, character of the sea in many areas. The Naval Oceanographic Office (MOO), formerly the United States Nevy Hydrographic Office (H.O.), has published many oceanographic atlases pre- senting oceanographic environmental information. These atlases have sum- marized available knowledge of many ocean properties in several principal ocean areas of the world. Among the most familiar properties that have been charted and analyzed are sea surface temperature, salinity, density, sound velocity, ice distribution, tides and currents, marine geology, sea and swell, and wind. Some H. 0. atlases have considered also the distri- butions of marine biological species, both plant and animal, as well as biological phenomena such as bioluminescence and the deep scattering la\ere These atlas charts have been prepared on an annual and seasonal basis, and, where a sufficiently high number of observations were available, monthly analyses were prepared. Other atlases, prepared by individuals and insti- tutions other than N00, have shown the distribution of some of the above: properties (1, 27). 12 Only one of these recent; N00 atlases I as included any of the optical properties of the ocean (46) . Properties which indicate the optical char- acter of a water mass include transparency, the beam attenuation coefficient, Forel color, and the vertical extinction coefficient (diffuse attenuation coefficient) . Some transparency and color contours were included in three other atlases published by H.O. in 1951 for Western Pacific coastal regions, including the waters off Indochina, Korea, and Japan (47-49). These con- tours were prepared from only a few measurements and have not been up- dated. It is believed that there exists no current atlas of Forel color data or transparency measurements as deternined by Secchi disc. B. PURPOSE The purpose of this investigation is :o examine the global distribu- tion of Secchi disc (transparency) measurements and color measurements vhich have been collected and reported to the United States National Oceanogrg phic Data Center (NODC, which has also been designated World Data Center A). The transparency values reported to NODC presumably were obtained with a whi te In this paper the terms transparency, visibility, Forel color, beam attenuation coefficient, vertical extinction coefficient, and diffuse at- tenuation coefficient have the following definitions: a. Transparency, sometimes called visibility, as measured by a Secchi disc is the average of the depths at which the disc disappears and reappears. b. Forel color is water color described by comparison with the Forel color scale or some modified scale such as the Forel-Ule Scale. c. Beam attenuation coefficient is the measure of the attenua- tion of a collimated light beam through a fixed path length. d. Vertical extinction coefficient, also called diffuse attenua- tion coefficient, is a measure of the exponential attenuation of down- welling radiation in the sea. 13 Secchi disc and the water colors were measured according to the code based on the Forel-Ule scale. These measurements have been reported along with the surface environmental information on the physical and chemical data forms for oceanographic stations. The dat&. tape provided by NODC contained records having transparency measurements or Forel-Ule color codes or both. On these records there were 67,257 transparency measurements and 23,482 color codes, representing NODC's holdings to June 1969. Figures LA, IB, 2A, and 2B give the distribution by Marsden square of the Secchi disc measurements and color codes. The number in the upper half of each square indicates the number of the Marsden square; the number in the lover naif indicates the number of observations in that Marsden square. The observations were reported by many countries as well as by different vessels and institutions of specific countries. It is seen from the distribution charts that observations .ire most numerous in the oceanic and coastal regions off Japan and China. These observations represent nearly 59 percent of the available transparency measurements and 69.5 per* cent of the available color determinations recorded in NODC's files. In general, the best area coverage was in the Northwest Pacific Ocean between the 180th meridian and the Asian coast. Significantly fewer mea- surements were on record for the Northeast Pacific Ocean between the 180th meridian and the western coast of the North American continent. Data for the South Pacific Ocean were almost non-existent, except for three Marscien squares immediately adjacent to the coasts of Ecuador and Peru in South America. NODC coverage in the Atlantic Ocean was sparse but has been used by Dickson (10), along with additional unpublished data and data on file outside NODC, to construct a chart showing the major transparency features for that area, his chart is presented in Appendix A. Data coverage in the 14 Indian Ocean was also limited; however, a chart showing the transparency and color trend for both monsoon seasons was constructed. Data for the Southern Ocean were most numerous in the vicinity of the Ross Sea and the Weddell Sea. The number of data points was still insufficient to give more than a genera] trend. This was also true for the Arctic Ocean. Data for the European Mediterranean, the American Mediterranean, and the Black Sea were again not numerous enough to indicate more than general trends. C. BACKGROUND ON THE SECCHI DISC The Secchi disc has been widely used to measure water transparency. Named for Professor Secchi, who first described its properties and use, the Secchi disc has never really been standardized with respect to its physical properties. However, considerable research has been devoted to the investigation of its utility as a practical instrument for the measure- ment of submarine daylight. Collier (8), in his translation of some re- marks on sea water transparency raode by Secchi and Commander Cialdi on the cruise during which the first Secchi disc experiments were performed, lists the experimental considerations of Secchi. These included the in- fluences of the size and color of the disc, shade from direct sunlight, height of observer above the water, altitude of the sun and clearness of the sky. The experiments in the Mediterranean were designed to determine the visibility of discs of different sizes and materials as influenced by the factors above. It was found that the depth of visibility increased with whiteness of the disc and with the altitude of the sun. Tyler (42) described the theory and use of the Secchi disc and demon- strated that the sum of the beam and diffuse attenuation coefficients could be calculated using a Secchi disc reading. He stated that only an average value of the coefficients could be found, and these only in the upper 70 m 15 of the ocean, lie listed some operational criteria which should be followed while taking measurements if the readings are to yield useful inf ormatio/i . Holmes (19), in a paper reporting field observations designed to help answer some of the questions and problems proposed by Tyler, used a Seccii disc in turbid coastal waters and determined a statistically significant relationship between the Secchi depth and team transmittance for the green region of the spectrum. He also examined t.he effect of different diameter discs in the turbid waters and found no significant variation in the depths at which the various discs disappeared front view. The use of a viewer placed below the surface of the water did not increase the depth of dis- appearance. He determined values of the beam and diffuse attenuation co- efficients from Secchi depths and from the Duntley-Preisendorf er equation of contrast reduction and found these values to have moderately large stand- ard errors. He commented that these errors might be acceptable in some studies. Further, biologists have established some useful relations between Secchi disc depths and the vertical extinction or diffuse attenuation co- efficient for downweliing irradiance. This coefficient is the sum of the coefficients of the absorption and scattering properties of a water mast. The determination of the extinction coefficient by Secchi disc measure- ment is useful in spite of the imprecise nature of the instrument. Poole and Atkins (31) have shown from data gathered in the English Channel that extinction coefficients for visible rays can be approximated by the equa- tion: v - hi ( -\ K = —• (m ) , s where K is the vertical extinction coefficient, and Z is the depth in s 16 meters at which the Secchi disc disappears from view. This relation has been found useful in the investigation of the ecology of fishes as re- ported by Murphy (29) and in the investigation of the primary organic pro- ductivity of the oceans by Ryther and Yentsch (36) among others. Holmes (19) suggested that the constant 1.7 in the Poole and Atkins equation be replaced by a value 1.44 for determining the extinction coefficient in turbid water. Graham (17), in his investigation in the Central and Eastern North Pacific Ocean, found excellent agreement between disc observations and extinction coefficients. His estimate of the extinction coefficient in- volved the Forel-Ule color scale index and the reciprocal of the Secchi disc depth and was corroborated by use of a submarine photometer. The photo- meter measured illumination intensities which were then used in the. equation I(z) = I(o) e'KZ , where I(o) and I(z) are the illumination intensities at the surface and at depth z respectively; K is the vertical extinction coefficient; and z is the depth in meters. Although Graham found good comparison between the ex- tinction coefficients determined by the different methods, he observed that extrapolation of the relationship between Secchi disc observations and ex- tinction coefficients should be done cautiously when comparing one oceanic environment to another. Emery (14) investigated the transparency of the waters off Southern California and showed that the Secchi disc readings taken there were closely Extinction coefficients and reciprocal vertical extinction coefficients computed from this relation are given in Table I. For example, the vertical extinction coefficient, K, for a Secchi depth, Zs , of 45 m is 0.038 m"*. The reciprocal of K for this Secchi depth is 26.5 m. 17 related to the concentrs^'on of organic debris. He found low transparency readings in nearshore regions and attributed them to the presence of sus- pended inorganic sediment derived as erosion products. Upwelling in the general area was evidenced by reduced transparency measurements. Postrna (32) investigated the relation between suspended material and the visibility of a Secchi disc in the coastal and inland waters of the Netherlands. He derived an empirical relation between the amounts and particle size of the suspended materials ard Secchi depth, i.e. i=0.34 S - D d 3 where D is the Secchi depth in cm; V is the volume of the particles in era ; and d is the diameter of the particles in cm. His investigations considered the effects en visibility of organic and inorganic particulate matter as well as the suspension of matter under tidal and non-tidal influences. Light attenuation in the North Sea and Dutch Wadden Sea in relation to Secchi disc visibility and suspended matter was examined by Otto (30) , who gave relationships between Secchi disc depths and both the vertical extinc- tion coefficient and the beam attenuation coef f icient . His paper summarized the relations between the vertical extinction coefficient and Secchi depth determined by different authors. He also presented the relationships be- tween Secchi depth and mean beam attenuation coefficient which were deter- mined at different times in different areas. An investigation of Secchi disc and color observations in the North Atlantic Ocean in 1964-1965 was made by Visser (52). He calculated the influence of wave-action on the visibility of the Secchi disc and found an empirical relation between the disc observation and the Forel color scale. This relation was given as: 100 - 0.26 Y + 1.9 , S 18 where S is the mean Secclii depth in meters, obtained from two discs of dia- meter one meter and one foot, and Y is the percent yellow, according to the Forel scale, of the sea water. Visser observed that this empirical relation was valid only for the ocean area of study. He determined that the clearest (most transparent) water has the lowest yellow content. Secchi deoths and Forcl-Ule color codes were plotted in Figures 87 through 91 in an attempt to examine a possible relation between disc observa tions and color codes. The observations plotted exhibited so much vari- ability that no simple empirical relation could be determined. Certainly the data do not suggest the single-valued relation which is implied by Visser1 s equation. For comparison, Visser's empirical relation is plotted on Figure 90, which presents Secchi depths and Forel-Ule color codes for the Washington-Oregon coastal region. Manheim and Meade (28) examined suspended matter in the surface waters off the /Atlantic continental margin from New England to Florida. They evaluated a relation between concentrations of suspended matter and the transparency and color of the water using the relation kd^ D = w where D is Secchi disc visibility; d is the mean diameter of particles; J) is the density of particles; w is weight of suspended matter; and k is a constant. They plotted suspended matter in milligrams per liter against Secchi depth in meters and found a strong, linear relation. A poorer relation between Forel color and weight concentration of parti- culates was found. The authors observed, however, that transitions in color of the water, when viewed from the air, are particularly striking and offer a potential method for estimating the suspended matter in sur- face waters over large areas if proper calibration techniques are used. 19 D. BACKGROUND ON THE COLOR OF THE SEA A description of the color of sea water has both subjective and objective aspects. The chromatic sensitivity and visual acuity of the observer's eye contribute to the subjective; aspect. From the objective viewpoint, Kalle (?.4) concluded that the blue color of sea water is due to scattering of light by water molecules or by minute suspended particles, small with respect to the wavelength of light. The blue color of the water is thus due to Rayleigh scattering, somewhat com- parable to the blue color of the sky. He also suggested that the presence of yellow substance (Gelbstoff) in combination with the blue water is re- sponsible for the scale of green colors observed along coastal regions as well as in the open sea. Shoulejkin (39) investigated the transmission of light through sea water and concluded that the color of the sea depends on four factors: selective absorption of light by water, scattering of light: by tiny sus- pended particles such as small bubbles of air or other gas, selective re- flections of light by other particles such as fine dust or plankton, and an admixture of the reflected light of the sky. He also derived from the Fresnel reflection formulae a. relation between the intensity of the color and the inclination of waves moving over the surface of the sea. He as- serted that the sea seems much more intensely colored from the lee side than from the weather side, where the surfaces of the waves are more steeply inclined. Tyler (41) examined the color of the ocean within the framework of modern colorimetry. He specified the geometry of lighting and the mea- surement of spectral flux; and he considered the spectral distribution of light in Pacific coastal water and in a fresh water pond into which plank- ton and yellow substance had been added. Measurements of the radiance 20 were compared and plotted on a chromatici'-y diagram. Tyler concluded that major factors in the ocean color are the pigments and chlorophyll contaired in the plankton. A summary of recent color research was given by Jerlov (21) who sum- marized various investigations of the factors which influence the color of the sea. He presented an extensive review of various theories which have been advanced to explain both the colcr and the changes in color of the ocean. E. FOREL-ULE COLOR SCALE The colo:: of the sea varies from a deep blue through an intense green to brown or brown-red. Prior to the development .of the Forel scale, water color was described qualitatively in terms of color shades ranging from dark blue to bluish green. Forel (16) recognized that such a description lacks precision and is dependent on the physiological characteristics of the observer. He devised a numerical scale made up of mixtures of two chemical solutions, ammoniacal blue copper sulfate and yellow potassium chromate, in varying proportions. The resulting series of solutions had colors ranging from blue to yellow-green. The vials of solution were num- bered, using the Roman numerals I to XI, and formed a .scale of hues at regular intervals between the blue and yellow-green endpoints. The scale was not adequate, however, for coastal waters, which may appear brown or brown-red as well. Ule (45) developed a scheme to provide a capability for measuring the brownish color of Baltic Sea waters. His scale similarly resulted from the combination of two chemical solutions, brown and green in color, in different amounts. The brown solution con- sisted of one-half gram of cobalt sulfate in strongly ammoniacal water 21 combined with distilled water to make a 100 ml solution. The green solu- tion was made by combining 65 parts of a potassium chromate solution with 35 parts of the copper sulfate solution. The resulting series was numbered from XI to XXI, where the number XI of the Ule scale was identical to the number XI of the Forel scale. Table IT. gives the conversion from scale number to proportion of each component solution. The combination of the two scales, the Forel-Ule scale, thus has a continuous sequence of number codes with which to report the estimation of sea water color in the deep oceanic regions and the transitions in color that occur as the depth diminishes into she How coastal regions. Other modifications to the Forel scale have been developed, and a review and description cf these modifications is giver, by Sower (40). The color of i ea water normally is determined with the Secchi disc at a depth of one meter providing the background against which a comparison is made between the sea water and the Forel-Ule scale. An atteif.pt is made to match the color of the sea water against: the Secchi disc with the color of one of the solution vials. The vials must be shielded from open sunlight while the determination is being made. When this is accomplished, the vial index is used to identify the proportions of the two colored water solu- tions. The number of the viol that blends most closely with the water color against the background of the disc is then recorded on the station data form. F, PREVIOUS INVESTIGATIONS On a global basis, optical measurements of the sea water were made as part of the investigation program of the Swedish Deep-Sea Expedition, which covered major ocean areas with the exception of the polar regions. How- ever, measurements were made using a beam transmittance meter, not a 22 Secchi disc, and were used by Jerlov (20) optically to classify water masses. The number of stations in each major ocean was quite small, and the tram - mittance survey is little more than a description of localized optical condi- tions. Dietrich (11) commented in a qualitative manner on the regional color and transparency characteristics of sea water. His comments on color and transparency were based largely on a consideration of the biological in- fluences of each region. Secchi d::.sc and color observations have been made in specific areas by many independent investigators. For example, the transparency of the waters of the Western Pacific Ocean and Indian Ocean were presented in a series of reports by Russell and Clarke (7, 34, and 35). Schott (38) constructed color contour? of the Atlantic Ocean and th? Mediterranean Sea. He expressed the color of the sea water in terms of che percent yellow fiolutijn according to the Forel scale. Secchi disc transparency measurements were made alon0 the coastal regions and in oceanic regions of the Northwestern Atlantic Ocean by Bumpus and Clarke (6) among others. Their report also included measurements taken by other investigators in regions north of 50 N Latitude. The authors used the Poole and Atkins (31) empirical relation to determine the extinc- tion coefficient and expressed the transparency contours in the area of study in terms of calculated extinction coefficients. In 1951 the U. S. Navy Hydrographic Office published three atlases on the marine geography, including water color and transparency contours, of the water? of the Sea of Japan, Korea, and Indochina (47-49). The Hydrographic Office also prepared a transparency chart of the North Atlantic Ocean based on all available transparency observations available up to December 1950 (51). The observations used were either 23 Secchi disc depths or hydrophotometer readings which were converted to equivalent Secchi depths. Isolines on the chart indicate the maximum transparency of the water reported throughout the year, and no seasonal changes are shown. Visser (personal communication) indicated that he has compiled many visibility measurements in the North Sea area but has not yet submitted his charts for publication. The number of his observations is considered to be far in excess of those available from KODC, and, for this reason, no contours of the KODC data were constructed !or that region. Arsen'yev and Voytov (2) charted the transparency of the Bering Sea water (Appendix B) and made a comparison between relative transparency snd plankton biomass. They determined sn inverse relationship between the two characteristics. In their paper it is reported that charts of water trans- parency and color for almost all of the marginal seas of the Soviet Union have been prepared. As previously mentioned, Dickson (10) has constructed a chart of the mean ocean transparency of the Atlantic Ocean between 15 S and 60 N Latitudes. His chart (Appendix A) probably represents the most comprehensive and recent report of Secchi disc observations for this area. G. TREATMENT OF DATA In order to handle the quantity of data involved, individual observa- tions were averaged in one-degree sub-squares within a Marsden square. A computer program was written to read the data, construct the one-degree sub-square grid, and sum and average all of the observations in a Marsden square. The averaged datum was rounded off to the next highest integer value if the fractional part was 0.5 or greater. These averaged values were plotted in the center of the one-degree square. This was done in all areas where the data density was very high. In other areas, where the 24 density of points was small, the data were plotted at the reported location of their measurement. Because the number of observations was insufficient to permit consideration on a month ly or seasonal basis, except for the Sea of Japan and the Indian Ocean, the data are presented as a mean distribu- tion. On each transparency and color chart tne data points are indicated ty a dot. On sorie charts, notably the Northeast Pacific Ocean transparency chart and the winter monsoon transparency chart for the Indian Ocean, data patches were contoured in a manner which might appear to be inconsistent with normal contouring procedures. Departures from normal procedures were made for areas where isolated observations were reported at some distance from other data. It was desired to show the relative value of the data groupings relative to the other data on the chart. Some contour lines were also terminated where no data were present to permit further extension. In the discussions of the various charts the descriptions of surface circulation were based on The Encyclopedia of Oceanography (15), except where specifically noted, and in the discussion of each color chart, the qualitative terms used to describe water colors (e.g. "deep-blue", "bluish-green") correspond to the color shades given in Table II. These color descriptions corresponding to the Forel numbers are those given in the Oceanographic Atlas of_ the Polar Seas (46) . 25 1 'L • DISCUSSION OF CONTOURS A. BERING SEA Data observations for the Bering Sea were contributed by Canada, Japan, Russia, and the United States. They were obtained mainly during the months of May to September in the period 1932 to 1966; of these, most were reported during the period 1957 to 1966. Figures 3 and 4 give the transparency and color for the Bering S< Minimum and maximum values of transparency were 6 and 29 m, respectively Color codes ranged from 2 to 9. Surface flew into the Bering Sea occurs mainly at Longitude 170 E, where the Alaskan Stream merges with the Western Subarctic Gyre with the forma- tion of a cyclonic eddy in the western section of the Sea. Another cyclonic eddy exists over the deep basin, and cyclonic and anticyclonic eddies are also formed in the eastern part of the sea. Currents over the continental shelf off the Alaskan coast are mainly tidal currents, except adjacent to the coastline, where river runoff flows northward and is discharged into the Chukchi Sea through the Bering Strait. Major river runoff comes from the Kuskokwim, Yukon, and Anadyr Rivers* The maximum plankton biomass occurs during the spring in surface waters over the continental shelf, followed by a reduction during the summer. A second bloom occurs during the fall. Zenkevitch (54) reports that the fall peok is less than that for the spring by an order of magnitude. As previously mentioned, Arsen'yev and Voytov (2) constructed charts to show the relative transparency and color of the Bering Sea during the sum- mer and winter seasons. Their charts are given for reference in Appendix B. Their summer chart shows a region of low transparency, less than 10 m, 26 extending from Longitude 180 to the eastern continental border. Two small areas with transparency greater than 10 in are shown within this region for the southeastern section of the Sea. A larger area, also within that region, whose transparency ranges from 10 to 15 m or greater, is shown for the rsgion just south of the Bering Strait. Transparency values for the western side of the Sea are greater than 10 ra, except for two coastal areas, where they are less than 10 n. A southern area has transparency values reported to be 15 m or greater. Figure 3 shows a region of low transparency, 10 m or less, along the coast of Alaska and along the coast of the western section of the Sea. The main body of the Sea has transparency in the range of 10 to 15 m. Several regions having higher transparency readings^ 15 m and greater, exist in the deeper porticnr. of the Sea as well as over the shallow shelf region. The color chart for summer, constructed by Arseu'yev and Voytov (Ap- pendix B) , shows considerably more variability than that shown in Figure 4. Their distribution indicates that the water over the shelf region is more discolored than that in the open basin. Figure 4, however shows no marked difference between the water color of the two regions. The Russian authors identified their color scale only as a "standard color scale," but did not specify it as the Forel-Ulc scale. Arsen'yev and Voytov stated that the data used for their charts were collected mainly during the years 1950 to 1956. Their Secchi data were less numerous, however, than those used to construct Figure 3, collected mainly during 1957 to 1966. Their color contours are based upon about twice the number of observations used in Figure 4. 27 B. SEA OF OKHOTSK Data for the Sea of Okhotsk are largely of Japanese origin and were obtained during the perr'.od 1935 to 1966. A few observations were reported by Russia and the United States. The majority of the observations were made between the years 1935 and 1942. Figures 5 and 6 give the transparency and water color for this region. Transparency values ranged between 3 and 25 m, and color codes ranged from 3 to 8. The bulk of the water in the Sea of Okhotsk is of Pacific origin and enters the Sea through the various straits between the Kurile Islands. Surface waters circulate in a cyclonic gyre which occupies the entire Sea . In addition, three stationary, anticyclonic eddies exist in the area of the southern basin. Numerous rivers empty into the Sea. ."•lost of the river discharge comes from the Amur River west of the northern part of Sakhalin Island, but many rivers from ^he surrounding Russian territory empty into the north-western and northern sections of the Sea. Rivers from the Kamchatka Peninsula, the Kurile Islands, Sakhalin, and Hokkaido also discharge into the Sea. The Sea of Okhotsk, according to Zenkevitch (54), has a high index of productivity with the highest concentration of plankton in the surface layers. A spring maximum concentration occurs throughout the whole body of water, but the autumn maximum occurs only in the southern portion of the Sea. The plankton population is distributed in varying proportions throughout the Sea. Transparency values would be expected to vary with the fluctuation, both seasonal and regional, in plankton population. The transparency contours, Figure 5, show a region of low trans- parency, 10 m or less, around the periphery of the sea. Several patches 28 of low transparency also exist in the vicinity of the Kurile Islands. This area is very rich in species of sea weeds and has an abundance of micro- organisms in the water (54) . These factors may contribure to the low transparency values found there. Although the northern region is characterized by a luxuriant planktcn growth, transparency values were not exceptionally low. A patch of rela- tively high transparency is shown to the north of Sakhalin Island. This may be attributed to the fact that these transparency measurements were taken mainly during the summer months when ;he plankton population is at a minimum. The low values near the coast are in regions where rivers dis- charge sediment-laden waters into the Sea. The color contours, Figure 6, show thai; the main body of the Sea is blue -green, with the regions near the coast becoming increasingly green. Three isolated small patches of greenish-blue water are shown at various positions in the Sea. An isolated patch of green water is also shown in the southern part of the Sea. C. SEA OF JAPAN Japanese hydrographical data for the inland Sea of Japan far exceed additional data reported by South Korea and Russia. The observations were made during all months of the year between 1927 and 1964. A large portion of the data was obtained during the period 1933 to 1941, and the remainder was gathered from 1953 to 1964. Since the number of observations for this region is quite large, the data were charted on a monthly basis, and additional charts showing mean transparency and water color as an average for all months were constructed using all the available KODC data for the Sea. Figures 7 through 19 show the overall mean transparency and the distribu- tion for each month, while Figures 20 through 32 show mean water color 29 during the same periods. The minimum and maximum transparency for the over- all average were 8 and 23 m respectively, and the range of color codes was from 2 to 6. Table III gives the range of transparency and water color codes for each monthly chart. In addition the average deviations from tha means of the observations for the one-degree squares within the area of the Sea were computed and are presented as the charts shown in Figures 33 through 58. These deviations were computed to illustrate what relative uncertaini- ties in data values might be expected elsewhere, when the number of observa- tions becomes sufficiently large. The deviations also can be used to indicate the relative confidence with which the contours can be viewed. The deep waters of the Sea of Japan are isolated from the trenches of the Pacific Ocean and adjacent seas. The main inflow into the Sea cones from the Korea Strait, through which the Tsushima Current enters and flows northward along the western coast of Honshu and Hokkaido. South of 47 N the Liman Current floisrs southward along the Siberian coast and completes the general counterclockwise circulation in the Sea of Japan. According to Zenkevitch (54) , the phytoplankton of the Sea have two periods of maximum bloom, one in the spring (March-April) and the other in autumn (September-October). He further states that the plankton popu- lation changes considerably, both qualitatively and quantitatively, with depth and with season. Cold-water plankton prevail in upper layers during the winter, but the plankton population changes sharply in summer. This population also has definite biogeographical zones within the Sea, the maxi- mum development being for the open sea. The variations in transparency to be expected throughout the Sea due to fluctuations in plankton population as well as other causes are shown in 30 Figures 7 through 19. April and May are shown to be the months of least transparency. The greatest transparency occurs during autumn and winter, although the fall season is not unproductive with respect to plankton growth. Greatest transparency generally occurs in the central sector of the Sea, and patches of water of relatively high transparency, greater than 25 m, appear in various places throughout the area. Figures 2 through 32 give the color contours for the Sea of Japan and generally show the Sea to be greenish-blue in color in the central section and bluish-green in nearshore regions. Little correlation is seen between the color and transparency contours. The most variable color contours are those for April and Kay, which is a period of marked diatom growth. The bloom of Septamber and October, however, is not sharply indicated in either the transparency or color charts. Both transparency and water color contours were presented in the Marine Geography (49) prepared by the U. S. Hydrographic Office in 1951 using data that was available up to 1941. The contours for the. Marine Geography we::e constructed to show seasonal variations in both properties. Figures 7 through 32 probably contain many of the same data as well as additional, more recent, observations. The general trend of both sets of contours is the same, although the marked seasonal changes suggested in the Geography 's con- tours are not seen in Figures 7 through 32. Uda (43) also discussed the transparency and color of the Sea of Japan and described the color as bluer (less than 3 on the Forel scale) in the warmer (eastern) sector than in the colder (western) sector and particularly green in the northern half of the Sea. He reported the transparency to be more than 25 m in the Tsushima Current area and less than 10 m in the colder sector. His descriptions of color and transparency are so general that com- parisons with Figures 7 through 32 are not really meaningful. 31 D. YELLOW SEA AND EAST CHINA SEA Data for the Yellov; Sea and the East China Sea were contributed by Japan, Russia, and South Korea, but the majority of the measurements v/er?. taken by Japan. Observations of transparercy and color were collected during all months of the year, and the collection period spanned the years 1932 to 1967, but most of the observations were obtained during the years 1932 to 1940. Figures 59 and 60 indicate the transparency and color contours for these waters. In the Yellow Sea, including the Gulf of Pohai, the trans- parency measurements had minimum and maximum values of 2 and 15' m, respec- tively. The color codes ranged from 2 to 7 . Transparency in the East- China Sea ranged from 2 to 26 m, and the color cedes ranged from 1 to 7. The seasonal Asiatic monsoons influence the surface circulation of this region. The principal current, the Kuroshio, enters the East China Sea from the Pacific Ocean between Taiwan and Yazama Island and extends north- ward along the continental slope. A portion of the Kuroshio extends west- ward into the Yellow Sea. In the western part of the East China Sea water from the Yellow Sea passes along the mainland of China, gradually deviating eastward. The cyclonic gyre that exists in the East China Sea is formed from these main currents. River runoff into the Yellow Sea and the East China Sea comes from several major rivers, including the Yellow River and the Yangtze River, as well as several smaller rivers along the Chinese coast. The mean trans- parency of the Yellow Sea is lowest, 2 m, at the mouth of the Yellow River. Transparency increases toward the middle basin of the Yellow Sea, while the color codes indicate light-green water for the regions of runoff and bluish- green water toward the same basin. Similarly, runoff from the Yangtze River 32 into the East China Sea was evidenced by low transparency values and color codes indicative of highly discolored waters. Kharchenko (25) reported that there ate several areas of upwelling in the East China Sea. The largest and most stationary one is an area of up- welling over die continental slope on the western side of the Sea. Three other areas of upwelling are associated with the divergence of the Kuroshio and in the eddies of cyclonic circulation. Deep water with a relatively high content of biogenous material is brought to the surface at this time. This feature of the East China Sea hydrography occurs mainly during the spring and summer seasons. The combination of river runoff and upwelling on the western side of the East China Sea would seem to account for the reduced values of transparency observed in that region,, The waters of the eastern region of the Sea, away from the influence of these two factors, are significantly more transparent, and the color codes of the eastern region indicate relatively blue water. Contours of water color and transparency for a portion of this region were given in H, 0. Publication No. 752 (47). This atlas, Marine Geography of Korean Waters, was published in 1951 and is based on unpublished Japanese data on file at the Kydrographic Office which was collected during the years 1931 to 1944. The atlas contours were constructed to show seasonal varia- tions of the two properties. It is believed that much of the data used in their preparation was used in the construction of Figures 59 and 60. The general trend of these contours is not dissimilar to the trend shown in the atlas figures. The atlas contours show seasonal structure, whereas Figures 59 and 60 are mean transparency and color charts for all seasons over many years. Figure 59 and the atlas contours show that the main body of the Yellow 33 Sea has transparency values of 10 to 15 m with considerably smaller values near the coas';. The region of least transparent water appears in the coastal area, particularly near the mouths of the t^o major rivers which discharge into the Yellow Sea. The color contours of the atlas and Figure 60 show the water of the Yellow Sea to be quite variable, with the regions of great- est variability occurring at the mouths of the Yellow and Yangtze Rivers. E. GULF OF TONKIN Data for the Gulf of Tonkin are mostly Russian observations, with a truch lesser number contributed by the United States and Japan. Most of the data were taken between April and October during the years 1935 to 1965, with the majority of observations reported during the period 1961 to 1965. Figures 61 and 62 give the contours of transparency measurements and color codes. The transparency data range from 4 to 30 m, and the range of color codes was from 2 to 9. The Gulf of Tonkin is fairly shallow, with the deepest part in the center having a depth of only 70 m. The Gulf is subject to the Asiatic monsoon wind system which influences the seasonal surface circulation pattern. The most transparent area of the Gulf is to the west of Hainan Island. Farther south, in the channel between Hainan and the coast of North Vietnam, the waters become more transparent. The waters of least transparency appear along the mainland shelf. There is a zone of mud, characteristic of the Red River Delta, which contributes to the low transparency found in that region. Contours of transparency and water color for the Gulf of Tonkin are given in H. 0. Publication No. 745 (48). This atlas, Marine Geography of Indochi.nese Water, shows only a single chart for the season July through December. The general trend of these color and transparency contours is 34 not greatly dissimilar to the trend shown in Figures 61 and 62. The atlas indicated that the Gulf vater was less transparent than suggested by Fig- ure 61. The m.iximum Secchi depth range reported in the atlas is 15 to 20 m, whereas the dsia utilized in Figure 61 show a maximum range of 20 to 25 m in* the same central area of the Gulf. The atlas color contours indicate that the Gulf water varies from blue- green at the southern extreme to a mixture of yellow-green and green-yellow near the Red River delta and yellowish-green in the western and northwestern coastal regions. Along the northeastern ami eastern coasts the water color vaiies from green to yellowish-g'reen. Figure 62 shows that the central basin is greenish-blue in color and changes to a bluish-green toward the coast. The coastal water was coded to indicate that the water is primarily green with a region of greenish-yellow water near the Red River delta. F. SOUTH CHINA SKA AND GULF OF THAILAND Japan's data observations in this region are extremely numerous. Other countries which have made data contributions include Russia, the Republic of China, the Republic of Germany, Thailand, the United Kingdom, and the United States. Data have been collected during all months of the year for the period 1907 to 1967, but the majority of observations were made during the years 1930 to 1941, Figures 63 and 64 give the transparency and color contours for this region. In the South China Sea the transparency measurements have minimum and maximum values of 4 and 42 m respectively. The range of color codes is 1 to 7 . In the Gulf of Thailand, the transparency observations have a mini- mum value of 4 m and a maximum value of 28 m, and the color codes range from 3 to 7. 35 This region is subject to the seasonal monsoons that characterize the climate of Southeast Asia. As a result, the surface circulation is sub- ject to seasonal variations which alter the direction of water flow through the area. The main interchange of surface water is through the Bashi Chan- nel, north of Luzon, and Karimata Strait, southwest of Borneo. Weak counter- currents exist at the eastern side of the Sea during both rncmsoon seasons. Upwelling occurs off the coast of central South Vietnam in midsummer. The major river runoff into the. waters of the South China Sea comes from the Mekong River. The runoff is at a maximum during the summer mon- soon season. Low transparency values were observed in this region, while higher values were found in the main basin of the Sea. Reduced values were found along the mainland shelf and in the waters over the Sunda Shelf. The color code distribution indicates that bluer water is found in the main basin of the Sea, and greenish-blue water is found near the coast and over the shallow Sunda Shelf region. The Gulf of Thailand is a shallow arm of the South China Sea with a mean depth of 45.5 m. Four large rivers empty into the head of the Gulf, as do many smaller ones along both shores. Heavy precipitation and runoff dilute the surface waters considerably. Seasonal variation in the surface circulation occurs with the seasonal monsoons. The combined effects of variable winds, tidal currents, freshwater runoff, and excessive precipita- tion produce localized areas of divergence and convergence. Organic produc- tivity in the Gulf is greater than that of the eastern side of the South China Sea due to vertical mixing and upwelling (15). The transparency of the Gulf water is less than that of the main basin of the South China Sea. The color of the Gulf water is nearly that of the coastal water of the Sea 36 except for an area at the head of the Gulf, where the color code index indicates considerable discoloration which night be attributed to the riv^r runoff. Contours of water color and transparency for the South China Sea and the Gulf of Thailand were given in H. 0. Publication No. 754 (48). This atlas, Marine Geography of Indochineso referenced unpublished Japan- ese data on file at the Hydrcgraphic Office which was obtained during the period 1931 tc 1944 as well as oceanographic data collected by the Nether- lands Meteorological Institute. These contours indicate seasonal variations in the two properties. Figures 63 and 64 probably contain some of the same data as well as additional, more recent data. Very little correlation seems to exist between the atlas contours and Figures 63 and 64. Both sett: of contours show the least transparent water of this regicn to be near the mouth of the Mekong River. 'Che atlas shows the extent of this region of low transparency to fluctuate with season. Figure 63 shows only the mean transparency over an extended period of time. The atlas indicates that the Gulf of Thailand is more transparent than suggested by the data used in Figure 63. The main body of the Gulf is shown in Figure 63 to be less than 20 m except for a small isolated region in the southern area. The atlas contours show a large expanse of water having transparency of 20 m or greater. Both the atlas contours and Figure 63 show that the transparency in the South China Sea varies between values which are less than 10 m at the coast and 30 m or greater in the open sea basin. The color of the main body of the Gulf of Thailand is shown in the atlas and in Figure 64 to be bluish-green. The main body of the South 37 China Sea is shown to be blue in the open sea and greenish-blue near the coast. The Mekong River is shown to have highly variable water in the atlas. Figure. 64 does not show this variability due to a lack of data for that area. G. GULF OF ALASKA Canada and the United States have reported the largest number of obser- vations for the Gulf of Alaska, but additional data have been contributed by Japan and Russia. Observations were taken during all months of the year during the years 1949 to 1968, with the majority of the data obtained during the period 1956 to 1966. Figure 65 gives the transparency contours for the area. Minimum and maximum values of transparency are 5 and 30 m respectively. No colo; observations were available for the Gulf. Subartic 'waters which flow into the Gulf of Alaska circulate around the irregular coastline in a vell-def ined cyclonic gyre. The coast of the Galf is indented and fringed with islands. Majcr river runoff into the Gulf coaies from the Copper, Susitna, and Matanuska Rivers. The lack of data in the region of their discharge prevented the effect of river runoff on transparency of the Gulf water to be shown. Uda (44), in his discussion of the oceanography of the Subartic Pacific Ocean, showed four charts of transparency constructed from Secchi dice mea- surements which included the Gulf of Alaska for the summers of 1955 through 1958. His contours show a marked random variation in transparency and ex- hibit the same general features as Figure 65 , constructed from much more recent data and not plotted by season. A direct comparison between the charts is not feasible. In general there are patches in the open Gulf water where transparency is 20 ra or greate-. The coastal waters shown in 38 Figure 65 as well as in Uda's charts generally have transparencies of less than 10 m. Uda attributes the patchiness of the . summer transparency profiles to variations in plankton population throughout the region. H. NORTH PACIFIC OCEAN Excluding the marginal seas of the North Pacific Ocean, charts shoving mean transparency and water color were prepared for this area between tie latitudes 10 S to 55 N. The data utilised in these charts were obtained during the period 1907 to 1967 by the following countries: Canada, China, Germany, Japan, Russia, and the United States. Most of these observa- tions were made during the last 30 years and are Japanese hydrographica! data. Figures 66 and 67 give the mean transparency and water color charts for this region. Transparency ranges fron 2 to 60 m and color codes range from 1 to 13. Transparency was plotted at 5-m contour intervals until it reached a value of 30 m. The region enclosed by the 30-m contour contained data which were quite variable and a 35-m contour lo.vel was not practical unless some of the data were ignored. To avoid this, the 35-m level was not drawn; and slashed and dotted areas were drawn to indicate ranges of data greater than 30 m. The dotted regions indicate a range of 40 to 50 m, and the slashed area denotes a range of 50 to 60 m. On the color chart, the isolated patches of single observations which differed from the sur- rounding area by one unit, either above or below the color code of the adjoining area, were not drawn. Surface currents in the Pacific are driven by the trade winds and the westerlies, and the surface flow is predominantly westward at low latitudes and eastward at high latitudes. At the continental borders, the zonal flows are diverted to form both north and south flowing currents at the 39 eastern and western boundaries, establishing cyclonic and anticyclonic gyres within the oceanic region. As shown in Figure 66, the transparency contours, particularly in the western area, exhibit the productivity characteristics of the Pacific water masses. The region of greatest transparency is located in the lower lati- tudes where, due to the strong stratification of the water, depletion of nutrients in the photic zone occurs. The tropical plankton population is reduced below that of the subpolar regions. In 1954, Bogorov (4) reported productivity in the boreal regions to be 20 times that of the tropical regions. This is also the region of bluest water, as seen in Figure- 66. The Kuroshio is notably less fertile than the Oyashio, and this distinction is seen on both the transparency and water color charts. The Kuroshio Cur- rent region is shown to have a transparency range of about 20 to 30 m and is deep blue t;o greenish-blue in color; the Oyashio has a transparency range of about 12 to 10 m and is bluish-green in color. These transparency rarges agree quite closely with those reported by Aruga and Monsi (3), who investi- gated the productivity in the region of the two currents in I960 and 1961 . On the northeastern side of the Ocean, the coastal regions near the Columbia River are extremely discolored and have water of low transparency. Offshore the transparency increases to values comparable to those recorded at the same latitude on the western side of the Ocean. I. EASTERN SOUTH PACIFIC OCEAN Although transparency measurements in the South Pacific Ocean as a whole are rather limited, over 1000 observations were reported from the oceanic region adjoining the coasts of Ecuador and Peru. A chart was constructed for this region between 10 N and 40 S Latitude and between 70 W and 115 W Longi tude. 40 Most of the observations for this area were reported by Peru, but additional data were contributed by Ecuador, Japan, Russia, and the United States. T'-ese observations were obtained during all months of the year between 1953 and 1967, but most of the data were recorded during the period 1963 to 1967. No Forel-Ule color codes were reported for the areg . Figure 63 gives the transparency contours for this area. Transpar- ency ranged from 3 to 38 m. The transparency distribution seems to be in good agreement with the surface circulation present in the area. Between latitudes of approximately 45 S, off the ccast of Chile, and 4 S? off northern Peru, the prevailing surface currents flow northward o^raliel to the coast nearshore, with increasing westward motion farther offshore. At about 4 S, the current merges with the South Equatorial Current, leaves the coast and flows west. The equatorward- flowing Peru (Humboldt) Current directly contributes to the abundance of marine life characteristic of the area. Upwelling or:f the coastal boundaries seems to occur during the whole year, but it is greater during the southern winter, since the x^ind intensity is greatest then. Upwelling brings to the surface a rich supply of nutrient elements and thus continually supports a high standing crop of phytoplanktcn and high rates of organic production. Coastal concentrations of organic material contribute to the cause for the low values of transparency shown in those areas on Figure 68. Transparency values increased offshore away from the coastal influences. J. NORTH ATLANTIC OCEAN Because of the recent work of Dickson (10), who compiled a chart showing the mean transparency of the Atlantic Ocean between latitudes of 41 15 S to 60 N (Appendix A), only the water color data reported for the Atlantic Ocean were used. These observations were contributed largely by Russia and the United States. A fev,T color reports were submitted by Brazil, the Congo, Venezuela, Nigeria, and the Netherlands. These data were obtain- ed between 1960 and 1968, with the majority of observations made during the period 1963 to 1968. Figure 69 gives the distribution of mean water color between latitudes 10 S and 50 N. Color codes ranged from 1 to 18. As previously mentioned, Schott (38) cons true ted a color chart of the Atlantic Ocean based on the Forel scale. His chart shows a color distri- bution of dee^' blue in the Sargasso Sea to green or yellow-green water in equatorial regions, in nearshore areas, and in higher latitudes. Figure 69 utilizes much more recent data and shows a color distribution ranging from deep blue to yellowish-brown water. The main body of the Atlantic in the mid-latitude region is shown to be blue in color with several patches of deep blue water. The data in the Sargasso Sea does not seem to indicate the deep blue reported by Schott. However, the number of observations in that area is far too small to make an accurate determination. Higher latitude regions are bluish-green to greenish-blue in color, and green water is shown south of Nova Scotia and in St. George's Chan- nel near Ireland. Coastal waters off North America and Europe and North- west Africa (above 5 N Latitude) are bluish-green and greenish-blue in color. The coastal waters off South America and Africa, south of 5 N Latitude, are markedly more discolored. The Niger and Congo Rivers empty into the Atlantic from Northwest Africa and make the African coastal water considerably more discolored than that off South America which is influenced by discharge from the Amazon and Orinoco Rivers. The oceanic region receiv- ing the Niger and Congo River discharges is at the junction of the South 42 Equatorial Current and the Equatorial Counter Current. A small anticyclonic gyre is established in the Gulf of Guinea. Highly variable color condi- tions are shown in this region. K. CARIBBEAN SEA The United States and Venezuela contributed most of the data for this sea. Three measurements taken by tv.ro Russian vessels were also reported for the area north of Venezuela. The data >-?ere collected during all months of the year during the period 1953 to 1967, with most of the observations; obtained during the years 1963 to 1967. Figures 70 and 71 gives the contours of transparency and color for the region. Figure 70 shows average minimum and maximum Secchi depths of 10 and 35 m, respectively. The average minimum and maximum color codes are shown in Figure 71 to be 2 and 9, respectively. The circulation in this area is from ei.st to west in the upper 1500 m. The source of water entering the area is the wind-driven Guiana Current. Most of the water is forced through the central section of the Lesser Antilleaia Island chain, principally in the passages north and south of St. Lucia Island. Major river runoff enters the Caribbean Sea from the Magdalena River in the northern part of Colombia. Secchi disc measurements were made in the Caribbean Sea by Curl (9) , during his investigation of primary productivity in the northern coastal waters of South America during October and November 1958. His investiga- tion covered the entire southern coastline from Trinidad to the Gulf of Darien. The Secchi disc data were used to establish the euphotic zone depth. Results of his investigation related transparency to primary produc- tion in the water in the vicinity of the Magdalena River. The lowest 43 transparency and production rates occurred at the mouth of the river. Greatest light penetration occurred in the eastern portion of the Gulf of Venezuela. Figure 70 shows that the area of greatest transparency and hluest water in the Caribbean Sea is along the axis of the Caribbean Current. Lower values of transparency appear along tie coastal regions. Upwelling exists along che eastern side of the Gulf of Venezuela, where low trans- parency would be expected. Another region of upwelling exists in the Gulf of Cariaco, which is also a region of relatively high biolog\-;al producti- vity. Transparency values in the region of the Gulf of Coriaco were low in comparison with water transparency away from the Gulf. However, these values were obtained at different times of the year and may indicate the low trans- parency usually associated with coastal regions as well as the influences of upwelling. No transparency measurements were obtained in the region of the Gulf of Venezuela. Several isolated patches of highly transparent water, 30 m or greater, are shown in the northern part of the Sea. The distribution of sea water color, Figure 71, shows that the coastal waters are bluish-green at the southwestern side of the Sea and greenish-blue at the southeastern side. A region of highly discolored water is shown northeast of the Gulf of Cariaco. Color codes of 7 to 9 were reported, indicating that the water is green to greenish-yellow. These measurements were taken in September, and the discoloration may be due to a high plankton concentration at that time. A region of green to light-green water is shown near the mouth of the Magdalena River, west of the Gulf of Venezuela. Curl (9) reported that the surface waters of this river flow eastward and the extent of this area of green water seems to be in agreement with the direction of that flow. A region of green water is 44 influenced by the inflow of surface water through the various channels between the island arc forming the eastern boundary to. the Sea. L, EAST SIBERIAN SEA, CHUKCHI SEA, AND BEAUFORT SEA Data for this region were contributed largely by the United States, but a lesser r were also reported by Pussia. The data were collected during the months of July, August, and September and were reported for the years 1933 to 1966. Host of the observations were obtained during the period 1957 to 1966. Figure 72 gives the transparency contours for this region. A mini- mum value of 2 m was reported near the coast of Siberia, while a maximum value of 35 m was reported for the open ocean north of Alaska. No color observations were reported for this area, r.or were transparency observa- tions reported north of 75 N Latitude. A small part of the eastern portion of the East Siberian Sea is shown on Figure 72. A region of low transparency, 10 m or less, exists along the coast of this shallow sea. Surface waters flow eastward along the coast into the Bering Strait. There are several rivers along the coast which discharge into the Sea, and the sediment-laden waters contribute to the low transparency values. The transparency of the .deeper waters has a maximum value of 16 m. The Chukchi Sea is the connection between the Arctic and Pacific Oceans Surface waters from the Pacific are carried into the Sea, and the current flows northward along the Alaskan coast. Part of the current is deflected to the west, while the remainder continues to flow along the Alaskan coast. A cyclonic flow pattern is established across the Sea; this pattern is best developed during the summer months. The water coming into the Sea has been affected by the discharge from the Yukon River south of the Bering Strait. 45 This effect is seen in the low transparency, less than 10 m, of the shallow water of the Strait. The circulation pattern of the Beaufort Sea is dominated by a well- defined anticyclonic gyre. Along the coast the currents depend on the local winds and are highly variable. Major river runoff into the Beaufo*t Sea is contributed by the Colville, MacKenzie, and Anderson Rivers as well as several smaller streams. A region of low transparency extends seaward along the Alaskan coast. Kearshore, the shelf has many gravel islands whose relief features are continually being modified by the action of strong offshore currents. The erosion products from this process and the sediment deposited by rivers provide a partial explanation for the reduced trans- parency found along the coast. The maximum value reported for the Beaufort Sea was 18 m in the water west of Banks Island. Transparency and water color distributions are shown in the Oceanogcaphic Atlas of the Polar Seas (46). These contours were constructed by the Kydro- graphic Office using all available data up to 1957. Figure 72 contains more recent data. The general trend of the atlas transparency contours and Fig- ure 72 is the same, except for the eastern section of the Beaufort Sea near Banks Island. The atlas contours indicate that the average transparency of the open water in that locality is 10 m or less. Figure 72 shows the trans- parency to be between 10 and 20 m. Particularly good agreement is shown in the Bering Strait area and in the southern part of the Chukchi Sea. Trans- parency measurements in the East Siberian Sea indicate that the average transparency of the open water is between 10 and 20 m. The values in the coastal region agree with the atlas. The atlas contours did not extend into the open v/ater area due to a lack of data at that time. 46 M. BARENTS SEA AND KARA SEA Data for this area were contributed mainly by Russia, with a lesser number of observations reported by Germany., Norway, and the United States. The observations were obtained during the months May to September during the period 1926 to 1967. Approximately two- thirds of the data were recorded prior to 1958. Figures 73 and 74 show transparency and water color for this region. In the Barents Sea transparency values ranged from a minimum of 7 m to a maximum of 39 m. Color codes ranged from 4 to 11. Transparency values for the Kara Sea had a minimum and maximum value of 3 and 24 m, respectively. The range of color codes was from 5 to 12. A branch of the Gulf Stream flows into the Barents Sea and circulates in a cyclonic gyre around the main body of the Sea. Arctic water also enters the Sec from the north, and numerous eddies exist in the central basin. The Barents Sea is characterized by the presence of the polar front at the boundary between the cold Arctic and warm Atlantic waters. Major river runoff into the Sea comes from the Perchora and Mezen Rivers, which empty into the southeastern portion of the Sea. At the polar front, vertical mixing occurs which brings to the surface a vast accumulation of nutrients which support a vast production of plank- ton. The Barents Sea is noted for its luxurious blooms of phytoplankton and a general abundance of organic life. The maximum development of both phytoplankton and zooplankton is during the summer months. Zenkevitch (54) reports a qualitative as well as quantitative variation in plankton composi- tion throughout the Barents Sea on a seasonal and annual basis. Because of this, the transparency of the Sea varies seasonally. 47 The Oceanographic Atlas of the Polar S_eas (46) presents contours of the average range of transparency and water color for the Barents and the Kara Seas. The data used for those contours were taken prior to 1957. The data used in Figures 73 and 74 were collected up to 1967. Approximately one-third of the transparency observations shown in the above figures are more recent t'lan the latest data shown in the atlas. All of the color codes in Figure 74 were reported since I960. Fipure 73 shows a region of relatively high transparency, 30 m or greater, due west of Novaya Zemyla. The central basin of the Sea surrounds this region with an area of water whose transparency is between 20 and 30 m. A .consider- able expanse is shown as well where the transparency is less than 20 m. This is in sharp contrast with the atlas which indicates that the entire central basin has a transparency range of 20 to 30 m. The water color distribution (Figure 74) presents a marked difference from the atlas contours, which indicate that most of the entire basin of the Barents Sea has an average color range of from 2 to 3 on the Forel scale, The data used in Figure 74 indicates an average range of from 5 to 6. The latter range corresponds to colors from green to light-green in contrast to the blue to greenish-blue suggested by the atlas. The Kara Sea is a shallow sea lying entirely over the continental shelf. A marked cyclonic gyre dominates the circulation pattern of the surface waters. A considerable amount of fresh water enters the Sea from the 0b and Yenisei Rivers in the southern portion of the Sea. Sand and silty- sand deposits are accumulated at the mouths of these rivers, and an abun- dance of fresh water flora are present there. The river discharge sets up a northward current, which diverges to the northeast, west,and southwest. Figures 73 and 74 show the effect of this river discharge. Very low trans- parency values were obtained in this region, and the Forel-Ule color codes indicate markedly discolored waters. 48 The deepest section of the Sea is located at the site of the Novaya Zemyla Trough, This region is relatively poor in marine life and has a low index of productivity. The highest transparency readings for the Sea were obtained in that area. As in the case of the Barents Sea, seasonal and regional fluctuations occur in the plankton population of the Kara Sea. Variations in trans- parency values occur concomitant with these fluctuations. Transparency and water color for the Kara Sea are shown in Figures 73 and 74 and have the same general trend p.s the figures shown in the atlas, although the atlas shows a much larger area of relatively highly transparent water in the central basin which extends farther north than indicated in the present work. Figure 73 shows the region of greatest transparency to be limited to the area over the deepest section of the Sea, while Figure 74 shows a pattern of more discolored water than that suggested by the atlas. N. BLACK SEA All of the data for the Black Sea is of Russian origin. Observations of transparency were made during all months of the year during the years 1923 to 1958. Most of the data were taken between 1923 and 1925. No reports of color measurements were given with the transparency data. Figure 75 shows the transparency distribution for the Black Sea. Minimum and maximum mean values were 4 and 25 m respectively. A cyclonic surface circulation pattern exists along the shores of the Black Sea. Two cyclonic gyres exist in the eastern and western parts of the Sea. River runoff into the western portion of the Sea comes mainly from the Danube, Dniester, and Dniepper Rivers of eastern Europe. Transparency values in this area were low in comparison with the values in the central basin. 49 Redfield, et al. (33), reports that nutrients in the Black Sea have accumulated to an extreme degree and are brought to the surface by verti- cal mixing. The water column is very stable, preventing the discharge of these nutrient-rich waters out of the sea basin, and thus supports a high organic productivity. As a result the floral and faunal populations of the Black Sea are greater than those of the Mediterranean. Zenkevitch (54) reports that portions of the Black Sea have both a temporary and permanent plankton population , and that marked changes, both seasonal and annual, are observed in the composition and quantity of plank- ton. Transparency measurements- would then be expected to vary as the popu- lation fluctuates. The maximum value of transparency coincides with the area of maximum depth of the Sea. The amount of plankton in the northwestern part of the Sea is reported by Zenkevitch to be always greater than that present in the open sea. This area also receives abundant river discharge. A combina- tion of these two factors, abundant river discharge and high productivity, contributes to the low transparency for the shallow northwestern part of the Black Sea. Zenkevitch reports, too, that the transparency of the open sea usually varies from 18 to 21 in and decreases near the coast. He stated that the maximum value observed in the Black Sea was 30 m. This corresponds to the maximum value reported in the data utilized in Figure 75. 0. MEDITERRANEAN SEA Russian, Yugoslavia , and the United States have collected the data reported for this region. The most numerous contributions were made by Russia and Yugoslavia. These observations were obtained during all months of the year in a period spanning the years 1925 to I960. Most of the data were taken during the period 1948 to 1958. 50 For charting purposes, the Mediterranean Sea was divided at 16 E Longitude. Figures 76 and 77 give the transparency contours fur I western and eastern regions respectively , and Figures 78 and 79 give the color code contours. In the western basin transparency values had a mini- mum value of 17 and a maximum value of 47 n, and the range of color codes; was from 2 to 4. In the eastern basin transparency measurements ran frcri 9 to 51 tn, while color codes ranged from 2 to 4. Surface water from the North Atlantic enters the Mediterranean through the Strait of Gibralter and follows the coast of North Africa. The waters spread out over the sea surface and generally flow in a cyclonic pattern The major river runoff into the western basin of the Mediterranean comes mainly from the Rhone River at the northwest part of the basin. The River empties into the northern Adriatic Sea. The Nile River provides the main river discharge into the southeastern part of the eastern basin. Numerous small rivers along the African and European coasts discharge into the Mediter ranean . Nutrient concentrations are very small in this Sea, and the productiv- ity is low. This lack of nutrients is in sharp contrast with the Black Sea, where nutrients tend to accumulate. The transparency observations taken in the Mediterranean Sea show that the two basins tend to be fairly transparent at their centers, while lower values occur along the continental coasts. The Mediterranean Sea is considerably more transparent than the neighboring Black Sea. The greatest transparency, 51 m, reported for the Mediterranean Sea is nearly twice that of the maximum value, 30 m, observed in the Black Sea. No obser- vations were taken in the immediate vicinity of the points of discharge of the major rivers, so the effect of river effluent on transparency is not seen. Nearly all of the color codes reported for the eastern basin shov/ the water to be nearly blue. The water of the Adriatic. Sea is greenish-blue in comparison to the blue water of the eastern basin. The .water of the western basin is blue in the central part of the basin, but that near the coast of Sicily is more greenish-blue, like Adriatic water. P. INDIAN OCEAN Data observations in the Indian Ocean were obtained largely by Japan. These were supplemented by data reported by India, Portugal, Russia, South Africa, and the United States. Measurements were taken during all months of the year between 1930 and 1966, but the majority were reported for the period 1963 to 1966. To the north of 10 S Latitude the surface currents vary greatly in conjunC' tion with the seasonal alteration in wind direction. The area then is charac- terized by a winter monsoon during which the winds blow offshore from the northeast and northwest and a summer monsoon during which the winds blow on- shore fro:;i the opposite direction. Tr; y and water color charts were constructed for both monsoon seasons, although the observations for the winter regime are far more numerous than those for the summer season. The winter monsoon encompasses the period November to April, and the summer monsoon pre- vails during Hay to September. These monsoon seasonal limits are those used by Dietrich (11) . Figures 82 and 83 present the transparency and color contours for the winter season , and Figures 80 and 81 give the two distributions for the summer regime. During the winter monsoon transparency varies between a minimum of 6 m in the Persian Gulf and a maximum of 46 m at several loca- tions in the open sea. Color codes ranged mainly from 1 to 4, although an isolated report of 13 was given off the tip of Somali. Transparency values After having c ted our charts we received Voytov's paper (55) in which he presents his own chart for this season. The charts are in essential agreement. 52 during the summer season had a minimum of 4 m in the Bay of Bengal and a maximum of 45 m, which was reported for the Mozambique Channel and to the west of Sumatia. The range of color codes was from 1 to 10. As Figure E 0 indicates, most of the transparency data taxen during the summer monsoon were collected in three general areas: the northeast section of the Indian Ocean including the Bay of Bengal; the Red Sea and the Gulf of Aden; and the Mozambique Channel. Color determinations were made almost exclusively in the northeast section. Upwelling between the inland of Java and Australia occurs during the; southwest monsoon, and the area 'is reported to be highly productive by Bogorov and Bass (5). However, the transparency data do not show the effect of plankton production to any great extent. Values along the Java and northwest Australian coasts indicate water of relatively high trans- parency, generally greater than 20 m. A small patch of reduced transparency is shown off northwest Australia, but the transparency is also shown to be increasing toward the coast. Wyrtki (53) investigated summer season upwelling in this region and stated that the low transparency indicated a high concentration os sus- pended matter. He reported the transparency in terms of the vertical ex- tinction coefficient and showed that the distribution of the extinction coefficient resembled closely that: of the plankton biomass. Using the Poole and Atkins (31) empirical equation relating the vertical extinction coefficient to Secchi depth (Table I), Secchi depths were computed from Wyrtki' s coef f icients c A range of 8.5 to 11.3 m was computed from extinc- tion coefficients which ranged from 0.15 to 0.20 m or greater » These values are about one-half of the transparency values shown in Figure 80 which were obtained during the same months, although not necessarily during 53 the same yean;, as Wyrtki's data. Color determinations made in this region show the water to be deep blue to blue in most of the area. Northwest of Australia the water was greenish-blue to bluish-green. Neither water co':.or nor transparency measurements in this area show the effect of high concen- trations of plankton biomass. There exists in the Red Sea a narrow trough in the central sector which is bordered by broad reef-studded shelves. This deep seaway has an inflow from the Gulf of Aden throughout much of the year. No rivers flow into the Red oea and little water enters from the Suez Canal. Primary production in the Red Sea is generally low, although occasionally there are blooms of the algae from which the Red Sea supposedly derives its name, producing regions of discolored water of presumably low transparency. Figure 80 shows the transparency in the central basin of the Sea to be rela« tively high indicating the absence of river discharge and standing plank;on crop. Reduced values, approximately 15 m, were reported over the shallow sill at the southern extreme of the Red Sea. The Somali coast is also characterized by strong coastal upwelling during thf summer monsoon season (38) . Low transparency values and dis- colored water would be expected to be present in the area. Figures 80 and 81 indicate that neither transparency nor color show the effect of up- welling in the rcr/.lon. Both properties have values approximately equal to those reported in the upwelling region northwest of Australia. The Mozambique Channel is described by Ryther, et al. (36), as being of intermediate productivity. A transparency range of 30 to 40 m is shown in Figure 80 for this region. These values are, somewhat unexpectedly, within the range reported for the highly productive regions in the north- western part of the Sea. 54 A much more complete distribution of transparency and water color is presented for the winter monsoon season in Figures 82 and 83. Transparency shows marked variations throughout the Indian Ocean area. In areas where comparison was possible little difference is apparent between the two seasons in either transparency or water color. During the winter monsoon season the main body of the Indian Ocean, as shown in Figure 82, generally lias transparency between 20 and 30 m. Not unexpectedly, along some coastal regions, notably in the Arabian Sea, Gulf of Aden, and in the water off Somali, transparency is less than 20 m. Marked fluctuations in productivity were noted by .Ryther, et al. , (36) , for the western section of the Indian Ocean, but the regions of very high pro- ductivity are rot clearly indicated by the transparency data. Not uracil change in transparency is noted between the eastern and western sections of the Ocean. The wirter color contours, Figure 83, show little change from that for the summer season. Water color is mainly blue with patch.es of deep blue and greenish-blue water occuring within the oceanic region. Q. SOUTHERN GO Data observations for the Southern Ocean were contributed by six countries Argentina, Germany, Japan, Russia, the United Kingdom, and the United States. Observations were obtained during 11 months of the year, but most were made during December through February. The collection period spanned the years 1912 to 1968, with the majority of data reported during the period 1958 to 1968. Secchi disc measurements in the Southern Ocean were made largely in the Ross Sea and the Weddell Sea. There were also reported observations in the open seas of the Indian Ocean sector from 170 E to 10 E Longitude. Some 55 data were taken in the seas west of the Antarctic Peninsula between 60 W and 100 W Longitude. Nearly all of the data we::e reported in the seas south of 60 S Latitude , Figure 84 indicates the distribution of Secchi disc mea- surements. A transparency minimum of 3 m and a maximum of 41 m were re- ported. The surface circulation pattern in the Southern Ocean is influenced by the East Wind Drift which prevails around the periphery of the Antarctic continent. ; is separated from the West Wind Drift on the north by the Antarctic Divergence Zone which is an area of general upwelling. The con- figuration of the continent and the bottom topography influence the forma- tion of eddies and countercurrents which deflect the surface flow across the divergence zone into the West Wind Drift. The water flow is from east to west across the Ross Sea and along the border of the continent from Victoria Land to Queen Maud Land. A well-defined clockwise gyre is pre- sent within the Weddell Sea. Another clockwise gyre is formed on the west side of the Antarctic Peninsula and the surface flow is deflected north. The West Wind Drift influences surface flow cast and northeast around the continent. The circulation has influenced the high fertility associated with the waters of the Southern Ocean. The euphotic layer is very stable, and high concentrations of phytoplankton are found in these waters. Phytoplankton concentrations were shewn by Hart (18) to be at a maximum during the Ant- arctic summer. The geographic variation in transparency corresponds to the geographic variation in productivity. The Weddell Sea exhibits regional variations in productivity according to El-Sayed and Mandelli (13), with the northern region more productive than either the eastern or southern areas. The eastern part is lower in 56 productivity than either northern or soutl rn parts. Transparency oj: the eastern water would thus be expected to be greater than that of the other region;:, while the transparency of the northern region would be les s. This regional trend in transparency is indicated by the data presented in Figure 84. The coastal cater west of the Antarctic Peninsula are reported by El- Sayed (12) to be highly productive, and a region of low transparency at the tip of the Peninsula was found corresponding to the areas of high produc- tivity. Regional variations in transparency in the Ross Sea and the Indian Ocean sector of Antarctica were not compared with regional variations in productivity because the productivity measurements in these areas seem to be limited to the investigation of plankton productivity under the sea ice. In general, regions of low transparency wera found at the border of I continent, and higher transparency values were found farther away from the coast. Figure 86 shows the transparency distribution for the Ross Se . There were only 15 reports of Forel-Ule color codes throughout this area. Figure 85 indicates the position and value of these measurements. Three values at one location, south of the tip of Argentina, were averaged; hence 13 values appear on the chart. The color codes range in value from a minimum of 3 to a maximum of 13. The minimum and maximum values appeared in the Weddell Sea where most of the observations were made. The distri- bution of reported values in the Weddell Sea was random, and, due to the paucity of color data, no distinct color pattern is apparent. 57 III. REIAT I v BETWEEN SECCIII DEPTHS AND FOREL-ULE COLOR CODES In an attempt to examine a possible relationship between transparency and water color for the data presented, five graphs of Secchi disc depths. vs. Forel-Ule color codes were plotted for five ocean regions. These regions were plotted showing the data from either a single Marsden square or as a combination of two or more Marsden squares. An area in each of the Atlantic, West Pacific, and Indian Oceans was chosen £.s being representative of open ocean areas. An area adjoining the hinj Oregon coast was selected as representing a coastal region, and another coastal region, the Gulf of Tonkin, was selected to examine color and clarity in a shallow semi-enclosed area. The selection of the Marsden squares depended on the number of transparency and color observations available in each region to give a reasonable represent- ation of their distribution. The results of plotting the tv;o parameters are given as the scatter diagrams, Figures 87 through 91. It was believed that water which is highly transparent would have a low Forel-Ule scale number, since the higher transparency generally indicates the absence of suspended materials. That is, water color is due to selective absorption by the water molecules themselves and the upward light emanation from multiple scattering by these molecules. According to Jerlov (21), this latter factor is responsible for the brilliant blue color of the ocean. He further states that in turbid waters the selective absorption by parti- cles and yellow substance, sometimes called Gelbstoff, shifts to the longer portion of the spectrum, and a change in color is observed. Turbid waters generally have low transparency, and yellow substance decreases the blueness of the water, which would then be described by a larger scale code number relative to the scale code describing water without yellow substance. Thus an inverse relationship between transparency and water color was expected. 58 Joseph (23) made a comparison betw n I r« i sparency and a modified Forel color scale for two different bodies of water and showed the two propertirr. to be inversely related. His graphs also suggest, for the data points con- sidered, that the relation between transparency and water color is single- valued; that is, for each color scale value only one value of transparency exists. However, it should be noted that in the paper referred to only five pairs of values were plotted for one area and seven pairs for the other. Jerlov (2'J) stated that the character of the upward-travelling light is intimately connected with the color of the sea, but he gave no specific quantitative reference to a transparency value and color scale number. Graham (17) referenced Jerlov's remarks in his paper and further stated that information provided by the Sccchi disc and Forel-Ule color is not indepen- dent. He used both measurements in regression formulae to estimate extinc- tion coefficients. As shown in Figures 87 through 91, no such relationship appears to be verified by the data in any of the regions which were considered. Isolated instances of high transparency accompanied by a low color code, as well as water of low transparency with high color code, are certainly seen; however, the relationship between color codes and transparency generally is highly variable. It is seen in nearly all these figures, particularly at the low end of the color scale, that waters whose transparencies differ by as much as 20 m have been described by the same color code. At the higher end of the color scale a similar situation exists; however, the range between trans- parencies described by the same color code is somewhat smaller. This is seen most clearly in Figure 90. This lack of positive correlation between Secchi disc depth and Forel-Ule color code suggests the independent nature of these two parameters. 59 IV o CONCLUSIC Transparency and color of ocean regions, are generally quite variable, Little correlation seems to exist between the transparency and water color contou Transparency generally is low in nearshore regions and increases seaward. Transparency in regions of river runoff some tiroes reached the low value o." 4 m. 7'iie highest transparency reading was 60 m in the tropicol western North Pacific Ocean. Water of low transparency generally is more discolored than water which is more transparent, although waters whose transparencies differed by as ciuch as 20 m often were described by the same color code. Regions characterized by regional trends in plankton production general- ly had regional trends in transparency corresponding to the areas of con- centration of plankton. However, in the Indian Ocean regional trends in plankton production did not have corresponding trends in transparency mea- surements. Areas where productivity has been shown to be high had trans- parency values of the same magnitude of those found in relatively unproduc- tive areas. Upwelling, which occurs along the Peru and Ecuador coast during most of the year, was evidenced by low mean transparency readings along the whole coast. Seasonal upwelling in other regions was not spec! f ically identified by low transparency readings. Except in the Indian Ocean where the conditions were noted as above, the charts for the other regions were not constructed on a seasonal basis, and fluctuations in transparency readings due to upwelling could not be determined. 60 Fluctuations in transparency or color cue to variable factors associated with the Secchi disc or Forel-Ule color scale could not be determined in this study. 61 V. SI "IONS FOR FURTHER ; ICH In those areas where data are lacking, investigations should be made to collect transparency and color information so that complete area coverage charts could be presented. Data collection in areas already investigated should be continued so that seasonal and annual variations could be determined. The temperature, salinity, oxygen, chlorophyll, and particulate data obtained with the transparency and color data used in this study should bz analyzed to determine what correlation exists between transparency and color and each of those parameters. Since corre between transparency and color measurements and t*ie geographical distributions and concentrations of plankton have been suggested, these investigations should be continued to determine if quantitative rela- tionships can jc derived. Studies relating Secchi disc me; ents to other ocean parameters such as the vertical extinction coefficient should be continued to check further the empirical relationships that have been formulated. The Secchi disc and Forel-Ule color scale, as well as procedures for their use, should be standardized, so that fluctuations in the data due to variable factors associated with the disc, color scale, and field techniques could be eliminated. Variable factors influencing data taken with the Secchi disc, such as the altitude of the sun, wire angle, and meteorological factors should be further investigated to determine quantitatively their effects on trans- parency. 62 Verification of the transparency and water color charts by s of more accurate techniques of data measurement is highly desirable. This might be achieved through the application of satellite photography, which was utilised by Lepley (26) to observe water clarity in coastal regions. 63 100° 110" 120° 120° i 160° 170° IftO" 170c 160° 150° 140° 130° X. 100° 9i 100° 110° 120° 130° 140° 1S0° 160" 170° 1^0° 170° 1fe0° 150° 140° 130° 120° 110° 100° 9 Figure 1A. Sccchi Disc Observations between 100 E and 90 W Longitude 64 00° 90° 80° 70° 6P° 5,0° 40° 30 )0° 90° C-0° 70° 60° 50° 40° 30" 20 10 10° 20° 30° fltf 50° 60° 70° 80° 90° 100 Figure IB. Secchi Disc Observations between 100 W and 100 E Longitude 65 100°" lb° 120° 1.^0° 1>0° 150° 1^0° 170° 100° 170° 160° 160" 1^0" ijso" ifrO° 110° 100° 9 Figure 2A. Forel Color Code Observations between 100 E and 90 W Longitude 66 )V9P° 6,0" 70" 6,0° 5,0° 40" 3 0J 2,0° 1,0 10" 2 0° 3 0 40° 50° 60° 70" 80° 90° 1001 6o° 90° 80° 70° 60° 5 0° 40" 30° 20° 10" 0° 10° 20° 30" 40° 50° 60° 70° 80° 90° 100° Figure 28 . Forel Color Codes b< 100 W and 100 E Longitude 67 -O- >•■ r- O oa C • . o o ',-■ c- ,-'-' oi o © o ^^ o o c; .& o 0 134 Figure 63. Eastern South Pacific Ocean Transparency 135 Figure 69. North Atlantic Ocean Color Codes 136 V cu >-< CU w c <: u H CO c: C! -o i-( C3 CJ o CD u (Jit ■H 137 w G> •a o u u o 1-1 o u CO 0) w c en > XI ■H O t-i i CO 0 O u i-< r» o 0 l-l o 3 w CO •.-I u< 138 >> o c ai to -a c: ca CO »■' OJ « CO u to 140 0 w. 3 \ <9 i I %i4 ^ w -< 4J C) CO OJ u n M •H 145 146 o f v — o o o_ o o o in o u a o u to c CO J-i H C C w CO 0) CO a o o M d o M o CO 0) C! O ft (>J •■-I 0 o CO Q) U 3 00 •H 147 i? o o o- o 00 o in -a o u u o .-I o d o 03 GJ c o o w d o J- 1 CJ E w d o o f> o o d to •H o T5 in d M • O. r-t *»■ CD CJ fj 3 o M) n •H Pn 148 >, o CM t; C •"" CJ t-l csi cx o w *~ ■ u H o C O 0 •" w cl J2 -S "2 5j C •■H CO C O SrC -t-» f-< .. o >> i> .a £> * & o t— ( S s .; fci> CO g to S -< w v-~ o — < o o c c o o ^. S-i rt rj P- ft w w x a a ci M 1 1 3 •— > 0 CN 4-J v^ C 0 > o o U u ^ o o r- ■: > 0 CJ T3 c T> nl d TO > cy :-. !>i u » c d 01 -l D, < W G F- cfl o u t-i H m rt ,Q bo 1 in 0 c 4-> rJ f-l S< rt -*-» ft *-< ^i 01 O .' rl 0) f? CO * 1) > o o 5 .s >> rt o eo fM u o 1- a « 4-» rr ^ cl ^ ft 162 APPENDIX C The following four charts were prepared by Robert Owen of the U. S, Bureau of Commercial Fisheries, La Jolla, California (CALCOFI) . These charts are composite contours of data obtained during 1969 from CALCOFI cruises 6901, 5902, 6904-6912. 163 120' 115° 110° 40° 35° 30° 25" Secchi disc composite for January, February, March 1969. 20° 20° J- A. 1 L 120 110° 16-' -f— — r 120 WY 110° 40° 35° 30° 25" 40° Secchi disc composite for April, May, June 1969. 20° 20° ' ' 125° J L 120° .1 _J I L 115° 110° 165 166 ,25. 120* ■ ■ r ' "■ i i ' V T 1 1 1 ' ' \ CAPE "MtNOOClKiO tie.* no* — *y> 20* - 167 APfCNDIX D Trans icy of I South At! :'Q tic 168 w W < V) s: •u ex Q o w •H v o o w G o 13 0) 4J 3 CX O co i— < « U o U a •h •H 4J G C CJ •H U •H 4-1 IW CJ o o c o •H 4J O c •H 4-1 X to o •r-l 4J >•< CD > a. '.■: o ■ ■ <■• , C : CO >-< 0) jj ctv cr> ct\ ~--f m cs in GO CO LO <»" CO CN CN :H O O O O O O m i-O N M H CA CO N vO LO r-i NN CO cj ""i r-i r^ cn! co rH CM CM CO CO LO U ■ <3 • •M crv co r-~ o in vj- cm a G CN CO CO >«o II CN CO ■r o LO rH r> rH CN CN co c :,< O LO !--» v-O LO CO r- rH N N CO-JOO rH rH CN CO CO cr* r^- m CM 00 II II ^ CM •>: r 1G9 TABLE II Forel-Ule Color Scale, Proportions of Component Chemical Solutions and Color Shades pd w Q O O O Q O w g is W < u CO 3- s (J w >-< SOLUTION w (PARTS) o 53 W O COLOR 01 I 0 100 D p Blue 02 II 2 98 Blue 03 III 5 95 Greenish-Blue 04 IV 9 91 - Bluish-Green 05 V 14 86 Green 06 VI 20 80 Light -Green 07 VII 27 73 Yellowish -Green 08 VIII 35 65 Yellow-Grec n 09 IX 44 56 Green-Yellow 10 X 54 46 Greenish-Yellow 11 XI 65 35 Yellow 11 XI 0 100 12 XII 2 98 13 XIII 5 95 14 XIV 9 91 15 XV 14 86 16 XVI 20 80 17 XVII 27 73 18 XVIII 35 65 19 XIX 44 56 20 XX 54 46 21 XXI 65 35 170 TABLE III SEA OF JAPAN - MONTHLY MINIMA and MAXIMA MONTH January February March April May June July August September October November Dae ember Mil TRANS PA (METERS) MA" TRANSPARENCY (: BTERS) MINIMUM FOREL-ULE CODE 9 20 3 7 33 2 7 29 3 8 17 3 3 19 2 8 22 2 10 27 2 10 30 1 11 31 2 9 30 2 8 30 3 9 22 3 MAXIMUM FOREL-ULE CODE 6 5 5 6 6 6 4 5 6 5 5 5 171 c c c c c r c c c c c c c r C c c c c c c c c c c c c c c c PRrr ■ • M ■ LJTES 1 >E VALUE OF TH NTS A' ; ?L00 CODES RcPn;>TEf) IN A - i U ' I [ON of the! is also COMPUTi THE THE [ N THIS I i 3VIDEDBYTHE R« THE OAT A ^ A S "-SSIVE MARSDEN SQUARES ON MAGNET- DATA USFD : I RFC OR DEO IC TAPEo FOLLOWING SECTIONS REFER TO MARSOEN -S< ] 00) |,DEVF(100), , : » ^DEVF< ] I iS(100), LOO) ,WCC (1001 1 1 ••• (?) tSL ( 1 : DATA CAT A CAT A CAT A DATA DATA 0 / I t ] ,201 / >/iC D/t WCC/1 *0/i / ;. VF/100 V F / 1 0 '" ■ 0 / SL/5Co >t 51 D/ffSDMSS/1 ,0/ 0»53oOff5AoOff55oO»56oO»57oO T! LLi ' G SFCTII UTES ' GRID OF SUR-S H ,SI IS THP S "> V nP THF 1 I LS AI THE SOUTH AND NORTH LA? ITU ' *CH SUB-SOI THj Tt t F Ujn I W : AST A ST LONG) I UDE BOUNDAf LV^H IS THE LEFT LONGITUDE BOUNDARY 01 THE MARSDEN SOU'""",. 998 999 ,99 8 ) I T « - "3 1 • , ^2X, 9) " X 1=1,10 L(l ) S ( I ) + 3 )=LWB+I ) = L W ( I ) + 1 RSDEN SUB-SOUARE BOUNDARIES* ,/ ) WRIT E< ' FORMAT?' • ,32X,«LS" ,8X,«LN«,3Xff'LE ',/) no -K L S ( I ) = S Li\( I ) = L 1.(1 LE( I 1 K CO Cr^T INU? DO 1001 I=llff20 LS ( I ) = SL(2) LN( I )=l S( I )+l LW( I )=LW(I-10) LE( T ) = LW( I ) + l N U E DO I -21 i L S { I ) = S L ( 3 ) LN< I ) = LS( I )+l M I )--iVA 1-20) I r( I )=LW( I )+l ■ 1=21,40 L S ( I ) = S !. ( 4 ) L N ( I ) = L S ( I ) » 1 I J( I ) = LW(I-30) L E ( I ) = L W ( 172 1004 100 I I 1C 0 8 1C r Q c c r C c c c c c c c c c c c 1011 I • DO 1=41, L S ( I ) = S L i LN(I) = LSU)U ( I -40) i E I ) = L W ( I ) + 1 CC f I DO ICO1; I=51i L S ( I ) = S L ( 6 ) t I ) = L S ( I ) + 1 I m+i I ] u DO 1006 1=61, L S ( I) = S L { 7 ) LN( I MLS (I Ml I. '• ( I ML W< 1 ■ 1 I ] 1 -i ■( I )+l 7 1 , L S ( 1 I s L N ( i ) - L S M Ml LW( I MLW< 1-70) L ( I ML' (I Ml ! DO H 1=81, L S ( 1 I = S L ( 9 ) (I > + 1 I ( I )+l i - (; l , L S ( ' M S L ( 1 0 ) ■( I Ml L E ( I M L W { I M 1 I - ! , 1 LI) FORMAT ( 1H,25X, ( 10 i 1 14 60 70 ' , 1 S ( I , F 7 31 M( I ) ,LP( I ) ,LW( I ) 1 I THE FOLLOWING SECTH S THE DATA :'!ES '1 in APPLK .-SQUARE I Al L MEASURE- MENTS I P FOR ALL SUB-SQUAR! HTHIN Til GIVEN | UARE, f ND 4 Tl E RFW INO STATEMENT RE An [1 IS 01 DATA RFC OR OS, IN SURFS THAT WHEN THE FRCM THE BEGINNING PE I S THr LIST M S I NC I I I F ( N I F ( m !! ' G j 1 ! (4,11, S 1 H S Tl NU THE C at •; . SoF So : 0 ] 0 (4,1 5) AT ( =2 5) MS,NC SOI ' SOU ' NU ST DIGIT OF 1 ' UJ1SE NUMBER* ALL CRUISE. RS BEGINNING WITH i ■ AND HAT a WAS NO! CQNSID! , 13,53 X, II, 8X) ) I TO 3 d P. ( 2 ) 1 GO TO 25 AP(1 ) ) ] TO 14 '■■ XO,XI t YD,YM,YT 1, WCtTP I 2,12, II, 13, 12, II, 26X, 12,12, 35X) XP, X'\ XTS YD, YM, YTM DEGREES ITES,ANC TENTHS OF M] • L AT I TV :I~ SP CT I\ ■ IS THE F! 11 IS CCHI CISC DEPTH I I RSo 173 c r r. c c c c c c c c c c c c c c c c c c c c c c c c c c c 20 21 £ / IF( ( ir-( ( A I Ai on r IF( { ( J ) ) ( IF (7 • I I! (W WHFf = FL = F L 0 INU S( J S( J Co F c.( J S( J EQ.O) r { x { y j = 1. , i GT„ ( AL c ) = S )=Ni ) = ' ; >=N •>{YT" ) ) YTM=> n i+i D) + { FLOAT ( X D + ( FLOAT (XTM) Oo 1 ) ) / ( D)+( FLOAT (\ : ■ )*0«1 ) )/6 ■ ( J ) ) , ANOo ( Ai " ! I . LF ( J ) loANCo ( ALAT0GT0| > AT, I (Jl)l GO TO 21 G 0 TO ? 2 1 1 ♦ F C G A T ( T P ) SSIJI+1 GO TQ 10 SS( J H I ( WC ) S S ( J > + 1 !,IN E/ N ; i s e [S : SS IS IARE: NUMBER OF \NSPARENCY OBSERVATKP TOTAL VAi : EL COl OR CO THi NUMBER OF F . : I ( I) • f | i iNSo GO rn ] o .OF I Ot LOWING ECTIOI : ' IPUTES THF AVERi "! s ■ ' SUR! ; " ' ;. ACH --\> ■ i S iD « ! : I ■ . tfAU CF TR ISPAR- VELY IN EACH SU SOMA' ?5 4 6 4 7 48 49 51 50 WRI WR] SUB (; i !■• no I f ( sno IF( WCC l I CON Ti ( I f> 0 ( I ) ( I) TE( MAT T !" N 6,45 ( M • 6,46 ( ) Hi 5,47 ( 1H, 1=1 SS( I = SDM S S ( I I ,51 ( • 0 ■ UE I ) I ) MAR (1 1 S ♦ ,14,//) ,3 j Q S{ , * M X , ( X, v I I I ■• i ) / itN im X,!-2, M ■ ,4X, »T! » \ ^'jr.Y' , 2X, s AVI COLOR ', 2X, 1 s » , RFL I I OR* ) 4^ • , / , 1 1 1 ■; 3 X , ■ 1 ! C Y • , 3 X i 'OH 4? ro ( i > G "i I i MSS( I ) SS( I ) rS00( I ) 8X,I5,12X,F4 II IS" 1,10 x ( I ) WCC( I ) 3 1X,F49 1. ) ] 00 I J 1 1 14 THE FOLLOWING SECTION COMMUTES THE AVERAGE DEVIATION OF THE : NTS ' EACH GNE-DEGi SUB-SQUARE OF THE f I IARE, THE VARIABLE NAMES D<= VT ,0F VF , ADEVT , AOEVF HAVE THE FOLLOW ING orr no j IONS : DEVT IS TO D VIATION FROM THE ?-":A0 op THE I K D I V I r:iJ ALT R AN S P t i V E A S 1 1 T S «, DEVF IS TH I \T ION ■ ■ :• « THE -FAN 0* 1 HE INDIVI DUAL ' : S , ADEVT IS T\\r-_ WERAGE V LUE [ TOr TRANSI CY DEVIATIONS IN EACH MARSDEN S! UAREo ADf-VF IS ' WERAGE V ' I COl ( R CODE DEVIATIONS IN EACH SUB-SQUARi . REWIND 4 RCAD(4, His ENO=200) MSiNC I15X, X, I1,8X) IPC 1 0 8 ) I F ( 0 o M A R ( 2 )) 2 00 114 I F ( A P < 1 ) ) ' 30 CKSPACI ^ )(4, it 5) > ', XTM,YD, YM,Y1 ,TP 174 115 ^0 3 2 1 1 2 5 200 2 r: r- 2 C 7 ? r 9 210 225 IF( ( ir-{ ( Is I ■. [F( ( (J ) 5 I [ F ( T i ) E V T I F ( . DCVF GO T WRIT I F " v ■ W RTT FfW tA, 0R« , ■ D ' : I ' ( M I F ( M : S V ] ' ; AT( = FL =FL 0 J = l % ( ( J)=DE I 2 t I 2 , ! 0 ! . •> + ( > + ( . I I ( J ALAToL I I , I 3 , I ? , I 3 • T ? , I 2 , - c X ) • (XTMoEQoOn M ., ( V )) YT-^YT' *)+( FLOAT () ■ . . I )/< FLOAT ( YM) + ( FLOAT (YTM ) )0 1 ) )/( Do ( ALAToGl .LS ) VT I 0 ] ( E(6, AT < E< 6 AT( • 1' ,20 1H, ,20 AT( } LUE 2Xt ' AV X, ' , »D 1 = S ( I T ( I ) = 0 S ( I F( I )=D F ( < . I ) , A T ( « C * , 1 1 X , F IU NO 4 •M I ) 6) 4 2 X 7) 1 0 X , • M , ^ 2 . AT K 1 , ) ( 1 ) I . E F( I ) It I ) , 1 2 X , I •V. 1 ) lloANDol *L0N ., LT ..LF { J) ) ToL'M J ))) 2\ TO i ?r> ABS (S0D( J) -FLOAT (TP) ) T'j 3 ABS(WCC( J) -FLO AT ( WO ) R ( 1 ) RE1 , 14, //| I' ,4X,«" PARENCY* ,2X,'/! iGE« >r:« , IX, ' ■■■ ; ' ?X, 'FOREL' f 3X, 'COL ,1 X, 'VALUE' , 2X, ' V ~ ' \GE « ,1X, • V * /, E' ,2X, 'OBSERVATIONS' t3X,»1 . CY' <^X, 'OBSERVA : IS' , :;X,»fT; 1£JL§JLJ3 Lf ic. Woods Hole Oceano- phic In hed t eport) , IS : 8. Cialdi, A. and Secchi, P. A., "On the Transparency of the Sea," Translation by Professor Albert Collier, Limnology and Oceanography, 13, 391-394, 1968. 9. Curl, H. Jr., "Primary Production Measurements in the North Coastal Waters of South America," Deep Sea Research, 2(2), 183-189, I960. 10. Dickson, R. R„, On the Relationship between Ocean Transparency and the Depth of Sonic Scattering Layers in the I? tlantic, paper presented to the International Council for Exploration of the Sea, CM. 1969/0:7 Hydrographic Committee, 1969. 11. Dietrich, G., General Oceanography, p. 475-549, Interscience Publishers, New York, 1963. 12. El-Sayed, S. Z., "On the Productivity of the Southwest Atlantic Ocean and the Waters West of the Antarctic Peninsula," Biology of the Ant- artic Sea III, ed, by G. A, Llano and W. L. Schmitt, Antarctic Research Series, 1_1, 15-47, Horn-Shafer Company, Baltimore, 1967. 13. El-Sayed, S. Z., and Mandelli, E. F., "Primary Production and Standing Crop of Phytoplankton in the Weddell Sea and Drake Passage," Biology of the Antarctic Sea II, ede by G. A. Llano, Antarctic Research Series, 5_, 87-106, Garamond/Pridemark Press Inc., Baltimore, 1965. 176 14. Emery, K. 0., "Transparency of Water off Southern California," Transactions of the American Geophysical Union, 35(2) , 217-220, 1954. 15. Fairbridge, R. W., editor, The Encyclopedia of Oc.ear !vy_, v. 1, Reinhold Publishing Corporate -\, New York, 1021 p., 1966. 16. Forel, F. A., "Couleur de l'Eau," Abstract from La Leman (Vol. II), Lausanne, 462-487, 1895, (Translation by Jean Dutto, George Washington University, Washington, D. C.) 17. Graham, J. J., "Secchi Disc Observations and Extinction Coefficients in the Central and Eastern North Pacific Ocean," Limnology and Oceano- graphy, 11(2), 184-190, 1966. 18. Hart, T. J., "Notes on the Relation between Transparency and Planktrm Content of the Surface Water ol the Southern Ocean," Deep Sea Research, 9, 109-114, 1962. 19 « Holmes, R, W„, "The Secchi' Disc in Turbid Coastal Waters, ", preprint of article accepted for publication in Limnology and Oceanography. 20. Jerlov, N, G. , "Optical Studies of Ocean Waters," Reports of tl Swedish Deep-Sea Expedition 1947-1948, ed. by H. Potters son, Vol. Ill, 1-61, Elanders Boktrycki itiebolag, Sweden, 1951. 21. Jerlov, N, G. , "Factors Influencing the Colour of the Oceans," Studies on Oceanography, cd. by Y. Kozo, 260-264, University of Washington Press, 22. Jerlov, N, G., Optical Oceanography, Elsevier, Amsterdam, London, New York, 194 p., 1968. 23. Joseph J., "Meeresoptik," Landol t-Borns tcin Zahlenwerte end Func tionen Aus Physik, Chemie, Austronomi e ? Geophysik uni1^ lechnik, ed. by A. Eueken, Vol. Ill, 441-459, Springer-Verlag, Berlin, Gottingen, Heidelberg, 1952. 24. Kalle, K. „ "Zum Problem der Meereswasserfarbe, " Ann.d.Hydrogr. und Mar. Meteor., 66, 1-13, 1938. 25. Kharchenko, A. M. , "Currents and Water Masses in the East China Sea," Oceanology, 8(1), 28-36, 1968. 26. Lepley, L. K. "Coastal Water Clarity from Space Photographs," Photo- gramme trie Engineering, 34(7), 667-674, 1968. 27. Markerov, J. V., editor, Atj ^IfLt'^^i-JL^AL1!^ Water in the Pacific jDcean, Publishing House of the Academy. of Sciences of the USSR, Moscow, 119 p., 1963. 28. Manheim, F. T. and Meade, R. H., "Suspended Matter in Surface Waters of the Atlantic Continental Margin from Cape Code to the Florida Keys," Science, 167(3917), 371-376, 1970. 177 29. Murphy, G. I., "Effect of Water ( y on Albacore Catches," Limnology and Oceanography, 4(1), 86-93, 19 5 30. Otto, L. , "Light Attenuation in the North Sea and the Dutch Wadden Sea," Netherlands Journal of Sea Research, 3(1), 28-51, 1966. 31. Poole, H. H. and Atkins, W. R. G., "Photoelectric Measurement of Submarine Illumination throughout the Year," Journal of the Marine Biological Association of the United Kingdom, 16, 297-324, 1929. 32. Postma, II. , "Suspended Matter and Secchi Disc Visibility in Coastal. Waters," Netherlands Journal of Sea Research, .1(3), 359-390, 1961. 33. Redfield, A. C, Ketchum, B. H. and Richards, F. A., "The Influence of Organ '.cms on the Composition of ater," The Sea, ed. by Ma N« Hill, 2, 26-7/, Interscience Publishers, New York, 19b3. 34. Russell, H. D„ and Clarke, G. L., The Transparency o t Indi; Waters and Adjacent Area, Woods Hole Oceanog tic Institution Report 2, " 1944." 35. Russell, H. D. and Clarke, G. L. , Transparency of Ic c, Nor! and Central Ami m 'Jest In Territory and nv,'i;jii Island fcers, tiole Oceanographic Institution h4. 36. Ryther, J. H. and Yentsch C. S., "The Estimation of Phy top lank ton Production in the Ocean from Chlorophyll and Light Data," Limnology and Oceanography, 2(3), 281-286, 1957. 37. Ryther, J. H., Hall, J. R., Pease, A, K. , Bakum, A. and Jones, M. M. , "Primary Organic Production in Relation to the Chemistry and Hydro- graphy of the Western Indian Ocean," Limnology and Oceanography, 1J_(3) , 371-380, 1966. 38. Schott, G., Geographic des Atl.?ntischen Oceans, Verlag von C. Boysen, Hamburg, 3rd edition, 1942. 39. Shoulejkln, W. , "On the Color of the Sea," Physical- Review, 22(1) , 85-100, 1923. 40. Sower, L. A., The Forel Scale and its Modifications, U. S„ Navy Hydrographic Office Informal Oceanographic Manuscripts No. 35-60, Unpublished Manuscript, I960. 41. Tyler, J. E., "Colour of the Sea," Nature. 202(4939), 1262-1264, 1964. 42. Tyler, J. E., "The Secchi Disc," Limnology and Oceanography, 13(1), 1-6, 19"8. 43. Uda, M. , "Hydrographic a 1 Studies based on Simultaneous Oceanographi- cal Surveys Made in the Japan Sea," Records of Oceanographies! Works of Japan, 6, 19-107, 1934. 44. Uda, M. , "Oceanography of the Subarctic Pacific Ocean," Journal of the Fisheries Research Board of Canada, 20(1), 119-179, 1963. 45. Ule, W. , "Determination of Water Color in the Sea," Petermanns Mitteilu •■us Justus Perthus Geographischer Anstalt, v. 38, 70-71, Gotha, 1392. 46. U. S. Navy Hydrographic Office Publication No. 705, Oceanographic Atlas of the Polar Seas, Part II, Arctic, 1958. 47. U. So Navy Hydrographic Office Publication No. 752, Kn rinei G e ogra phy of Kor -tors, 8-9, 1951. 48. U. Sc Navy Hydrographic Office Publication No. 754, Marine G phy of Indochinese Waters, p. 36, 1951. 49. U. S. Navy Hydrographic Office Publication No. 757, Marine Geography of the S-a of Japan, 48-50, 1951. 50. U. S. Navy Hydrographic Office Study No. 27, Transparency of th< off Japan, 1943 . 51. U. S. I Hydrographic Office Chart H. 0. Misc 15222, Transparency Chart of the North / 1 c Ocean . 52. Visser, M. P., "Secchi Disc and Sea Colour Observations in the North Atlantic Ocean during the Navado III Cruise, 1964-1965, Aboard H. Neth, M0So 'Snellius1 (Royal Netherlands Navy)," Netherlands Journal of Sea Research, 2(4) » 553-563, 1967. 53. Wyrtki, K. , "The Upwelling in the Region Between Java and Australia during the South-East Monsoon," Australia Journal of Freshwater Research, 13(3), 217-225, 1962. 54. Zenkevitch, L. , B io I ogy of the S e ; • s of th e U „ S . S_, R . , Translated by S. Botcharskaya, Interscience Publishers, New York, 955 p., 1963. 55. Voytov, V. I., and M. G. Dement'yeva> Peer, no logy (Acad. Sci. USSR) 10(1), 35-37, 1970. (English trans.). 179 INITIAL DISTRIBUTION LIST No. Copies 1. Defense I station Center 2 Cameron Station Alexandria, Virginia 22314 2. Library, Code 0212 2 Naval Postgraduate School Monterey, California 93940 3. Department of Oceanography 3 Naval Postgraduate School Monterey > California 93940 4. 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GROUP 3 REPORT TITLE An Atlas of Secchi Disc Transparency Measurements and Forel-Ule Color Codes for the Oceans of the World 5 AuTHORlS) ( First name, middle initial, last name) Margaret Anne Frederick 6 REPORT DATE September 1970 la. TOTAL NO. OF PAGES 177 7b. NO. OF RETS 54 ea. CONTRACT OR GRANT NO. b. PROJECT NO »». ORIGINATOR'S REPORT NUMOER(S) »6. OTHER REPORT NOISI (Any other numbers that mny be assigned this r-fjort) 10 DISTRIBUTION STATEMENT This document has been approved for public release and sale; its distribution ii unlimited . li. supplementary notes 12. SPONSORING MILITARY ACTIVITY Naval Postgraduate School Monterey , California 93940 I. ABSTRACT An investigation was made of the global distribution of Secchi disc water transparency measurements and Forel-Ule water color codes which were on file at the National Oceanographic Data Center prior to June 1969. Charts were constructed for 17 major areas of the world's oceans to show the horizontal dis- tributions of transparency rnd/or color. Data generally were' presented as mean distributions. Charts were prepared showing the overall mean transparency and Forel-Ule color distribution for all of the data considered, except for the Si of Japan, for which monthly mean charts were constructed. Plots of transparency measurements against the corresponding color codes were also drawn for five selected areas. Transparency showed marked variations in each area considered. Generally it is greater in the central basins and decreases in coastal regions. Reduced transparency readings and discolored waters were noted for areas affected by river runoff, for areas of high organic productivity, and where standin plankton crops were found. Seasonal variations in transparency and color were not noted except for the Sea of Japan and the Indian Ocean (winter and summer). No simple relation between transparency and color was apparent. * \AT\ (PAGE 1) iHOHnM^nnaiimnHHHmiMmAMnaMBMB Ls» i*J> I NOV 65 I ~* i' I *J S/N 01 01 -807-661 1 187 Security Classification £-31403 TED Security Classification KEY WO R DS nsparency Sea Water Transparency Sea Water Color Forel Color 1-Ule Color Secchi Disc Transparency Distribution Forel-Ule Color Distribution Secchi Depths an Transparency Ocean Color Atlas of Ocerj) Transparen Atlss of Ocean Color Transparency and Color of the World's Ocean Hydrological Optics Optical Properties of Sea Water LINK A ROLE W T UU I NOV 65 i *", S/N 01 01 - I ( BACK } y Security Classification ouotcvi HMH.H MUNIEJCf.CA I DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL MONTEREY. CALIFORNIA 93943 Thesis 124644 F7871 Frederick c.l An atlas of Secchi disc transparency measurements and Forel- Ule color codes for the oceans of the world. Thesis F7871 r. 1 l 5 FEB 74 ■ 74 IO JUL 79 IO JUL j «;tiOCI 80 2 2 <4 6 U 26 a u 9 124644 Frederick An atlas of Secchi disc transparency measurements and Forel- Ule color codes for the oceans of the worJd. thesF7871 An atlas of Secchi disc transparency mea 3 2768 001 95999 2 DUDLEY KNOX LIBRARY i*