DISTRIBUTION OF PHOSPHATE IN THE SEA 



17 



Carnegie results in the central part of that ocean. At a 

 station at latitude 37° 44' north, longitude 13° 21' west, 

 he found 104 mg PO4 per cubic meter, which agrees 

 well with 111 mg per cubic meter as a mean for the 

 Carnegie stations in that general latitude. 



According to the phosphate section which Deacon 

 (1 933) constructed along the 30th meridian, this deep water 

 of low phosphate content extends southward to about lati- 

 tude 25° south at 2000 meters and beyond 30° south at 

 3500 meters. In this section, however, there was a 

 minimum phosphate concentration at about 3000 meters 

 below which there was an increase toward the bottom. 

 Such a feature has not been found anywhere in the Pacif- 

 ic Ocean. 



In connection with the difference in the quantities of 

 phosphate in the Atlantic and Pacific it is interesting to 

 compare the concentration of phosphate in the Arctic and 

 and Antarctic oceans. In the Atlantic east of Greenland 

 the oceanic polar front, or region of sinking, extends to 

 latitude 60° north (Meyer, 1928). The Carnegie at sta- 

 tion 10, which was in this vicinity, obtained a vertical 

 series of phosphate determinations to a depth of 3000 

 meters. At this station the phosphate content of the 

 water was almost uniformly 60 mg PO4 per cubic meter 

 from 500 to 3000 meters (see fig. C7). Similarly, 

 Brujewicz (1931) found in the Barents Sea, which is 

 north of the oceanic polar front, 90 to 105 mg PO4 per 

 cubic meter at the bottom and considerably less than 

 that amount near the surface. Sverdrup (1933) at nine 

 stations in the Arctic north of Spitzbergen found equally 

 low values. Below 100 meters at all stations the phos- 

 phate was rather uniformly distributed with depth. Most 

 of his values were below 97 mg PO4 per cubic meter 

 and only one was as high as 134 mg per cubic meter. 



Kreps and Verjbinskaya (1930, 1932) investigated 

 the seasonal variation in the concentration of nutrients 

 in the Barents Sea. Even in August and September when 

 there was an accumulation of phosphate in the bottom 

 water they never found concentrations exceeding 85 mg 

 PO4 per cubic meter. 



The Antarctic, on the other hand, contains much 

 more phosphate than the Arctic. At fourteen stations in 

 the Weddell Sea, Ruud (1930) found at 450 meters more 

 than 240 mg PO4 and at most stations about 260 mg PO4 

 per cubic meter as compared with less than 60 mg PO4 

 per cubic meter in the North Polar Front. Even at the 

 surface Ruud found high values, ranging from 121 to 

 208 mg PO4 per cubic meter. Wattenberg (1927a) found 

 similar conditions in the Atlantic at about 50° south. 

 Deacon (1933) reported 187 to 203 mg PO4 per cubic 

 meter in the deep water of the Antarctic. 



Thus, it seems to be well established that the North 

 Atlantic and Arctic oceans have a lower phosphate con- 

 tent than do the other oceans of the world. 



According to the distribution of salinity (Meyer, 

 1928) it is apparent that from the equator to latitude 40° 

 south the water of the South Atlantic between the depths 

 of 2000 and 3000 meters is typically North Atlantic wa- 

 ter, originating in the sinking area between latitudes 

 30° and 40° north. As this water, moves southward from 

 the central North Atlantic its phosphate content is grad- 

 ually augmented by the decomposition of sinking detri- 

 tus. In the South Atlantic this water is overlain by the 



Antarctic Intermediate Current which is rich in phos- 

 phate and which probably contributes some phosphate 

 from its lower border to the water below. Thus Deacon 

 (1933, p. 233) points out that the maximum amount of 

 phosphate occurs at the boundary between these two cur- 

 rents. He also indicates that "the greatest vertical 

 mixing between the two currents takes place between 

 latitudes 38° and 43° south so that the phosphate is not 

 lost from the antarctic zone but is returned to it in the 

 deep current." In the North Atlantic, on the other hand, 

 there is a slow increase in the concentration of phos- 

 phate to great depths, although it always remains rela- 

 tively low. This distribution of phosphate appears to be 

 peculiar to the North Atlantic. It does not occur in the 

 South Atlantic nor in the Pacific. 



The deep water of the North Atlantic is poor in phos- 

 phate because practically none of the water from which 

 it originates contains any great quantities of phosphate. 

 The sinking water in the Sargasso Sea contains very lit- 

 tle phosphate because of the peculiar hydrographic con- 

 ditions and because of the phytoplankton at the surface. 

 The North Atlantic Drift consists of warm surface water 

 with a low phosphate content. The Arctic water has been 

 shown by Brujewicz (1931) and Sverdrup (1933) to be 

 relatively poor in phosphate. The cold water in the 

 northernmost part of the Atlantic has a low phosphate 

 content as indicated by the Carnegie observations at sta- 

 tion 10. The only source from which the North Atlantic 

 receives water of a phosphate content corresponding to 

 that of the other oceans is the Antarctic Intermediate 

 Current which enters the tropical North Atlantic, but the 

 amount of water contributed by it to the North Atlantic 

 must be regarded as relatively small as compared with 

 the other sources. 



The South Atlantic Ocean is rich in phosphate be- 

 cause the main body of water between 2000 and 3000 me- 

 ters has traveled a comparatively great distance at a 

 level at which phosphate is being liberated, and because 

 the intermediate water above and the bottom water be- 

 low originate in the Antarctic where the concentration of 

 phosphate is high. - 



The deep water of the Pacific Ocean is rich in phos- 

 phate partly because it does not receive any large quan- 

 tities of water from other oceans that are poor in phos- 

 phate, and partly because it has lacked contact with the 

 convection layer for a long period of time. That the lat- 

 ter is true is indicated by the low oxygen content and the 

 remarkably uniform distribution of salinity and temper- 

 ature which prevail throughout the deep water of the Pa- 

 cific. 



The greater concentration of phosphate in the Ant- 

 arctic than in the Arctic can probably be accounted for 

 by the fact that the former ocean is in closer contact 

 with the deep water of the oceans adjacent to it. Sver- 

 drup (1931) has described the probable nature of the mix- 

 ing of the deep water of the Antarctic with that of the 

 oceans surrounding it. The Arctic, on the other hand, 

 because it is separated from the other oceans by land 

 masses and oceanic ridges, does not receive water from 

 other oceans rich in phosphate. The water which it does 

 receive from the Atlantic and the Pacific must be from 

 relatively near the surface, where the phosphate content 

 is low. 



