7 o DISCOVERY REPORTS 



North of the Antarctic convergence maximum phosphate in this section occurs either 

 at or close to the depth of the salinity minimum of the intermediate current. In general 

 there is slightly less phosphate in the eastern side of the South Atlantic Ocean than in 

 the western side, and this accords with the fact that the strength of the intermediate 

 current is not quite so great in the eastern part of the ocean as in the west. 



In late August 1930 a section was made south-south-west from Cape Town (Sts. 414- 

 421, 449-452). The phosphate content at the salinity minimum of the intermediate water 

 varied between 92 mg. and 1 54 mg., being greatest at the northern end of the section. The 

 depth of the salinity minimum of the layer varied about 200 m. throughout the section 

 and in general was between 600 and 800 m. Phosphate was greatest at the positions 

 farther from the surface. 



In late March 1935, south of Cape Town (Sts. 1554— 1557, section 4, Plate VII), the 

 phosphate content at the salinity minimum of the intermediate water varied between 

 141 mg. and 116 mg., being again greatest towards the north. 



In September 1930 a section in a south-easterly direction was made from Port Eliza- 

 beth towards the subtropical convergence (Sts. 424-435). The phosphate content of the 

 salinity minimum in the intermediate current was 157 mg. near the coast of South Africa 

 and between 125 mg. and 135 mg. at the southern end of the section. Near the coast, 

 however, the depth of salinity minimum of the layer was 1500 m. as against 800 m. 

 towards the south. This difference of depth of the intermediate water may well be 

 significant, as it is reasonable to suppose that there are less plankton organisms at the 

 greater depth. It would seem that south of South Africa the phosphate content of the 

 intermediate current is greater than in the Atlantic Ocean proper. The northward 

 movement of the current in the area south of South Africa is small compared with that 

 in the Atlantic Ocean farther to the west, and it is possible that the slowing down of the 

 northward movement in this current has the effect of restricting the decomposition into 

 phosphate from being spread over such a large area as in the Atlantic. The amount 

 of North Indian Ocean deep water in the upper layers of the warm deep water in the 

 vicinity of South Africa is not known for certain, but the upper layers do contain 

 water from this source. Our section (6, Plate X) to Guardafui in 1935 showed that the 

 North Indian deep water has a very high phosphate content, so that any mixing between 

 the bottom of the Antarctic intermediate current and the upper layers of the warm deep 

 current, which latter contains water of North Indian origin, would result in phosphate 

 being added to the lower part of the intermediate current. 



The phosphate distribution in the Antarctic intermediate current in the western part 

 of the Indian Ocean is shown in Plate X. North of the Atlantic-Indian cross-ridge the 

 depth of the salinity minimum of the layer is about 800 m., but when the section comes 

 within the sphere of the Agulhas current system the depth of the whole layer is depressed 

 so that the salinity minimum is found at about 1 500 m. only to rise again closer to the 

 surface towards the north. The phosphate at this position in the current is of the order 

 135-145 mg. at the greater depth and between 95 mg. and 129 mg. where the salinity 

 minimum is closer to the surface. The distribution fluctuates towards the north in a series 



