202 



DISCOVERY REPORTS 



to greater depths offshore. In places there is a layer of maximal phosphate off the edge of the conti- 

 nental shelf. This coincides approximately in depth with the layer of minimal oxygen, but like the 

 maximal phosphate layer in the equatorial parts of the ocean, it is much less well defined than the 



STATIONS WSIO50 



SEA MILES I 



OFFSHORE 175 

 O- 



IOO- 



200- 



WSI05S 

 I 



WSI05I 

 I 



WSIO50 



400 



Fig. 53. Distribution of phosphate (mg. ats. P/m. 3 ). Section off the mouth of Orange river, 21-24 September 1950, 



survey II. Positions of stations are shown in Fig. 2. 



STATIONS WS98G 



SEA MILES I 



OFFSHORE 100 



O 



WS987 



Q 200 



Fig. 54. Distribution of phosphate (mg. ats. P/m. 3 ). Section off Sylvia Hill, 25-27 September 1950, survey II. 



Positions of stations are shown in Fig. 2. 



oxygen minimum layer, and the phosphate concentration more often increases almost regularly to 

 greater depths. The maximum concentration is reached in the antarctic intermediate water. 



In the layer of minimal oxygen, however, the inorganic phosphate concentration reaches values of 

 about 2-0 mg. ats. P/m. 3 With upwelling, this extremely phosphate-rich water is brought up on to the 

 continental shelf, where it provides the necessary nutriment and permits the growth of the heavy 

 crops of phytoplankton in the coastal waters. In several of the sections it will be apparent that the 



