62 DISCOVERY REPORTS 



Durban, showed that the surface phosphate content was zero throughout the entire 

 zone. A month later in the previous year in subtropical water between the Crozets 

 and Durban (Sts. 1370-1373), the surface phosphate value was 20 mg. in the south of 

 the zone and less than 5 mg. near the coast at Durban. 



At the subtropical zone stations (section 7, Plate XII, Sts. 871-876), across the 

 South Indian Ocean between Enderby Land and Fremantle, the surface phosphate in 

 May 1932 was 48 mg. in the south of the zone and decreased to 10 mg. near Fremantle. 

 The subtropical convergence is found not very far south of Melbourne and Tasmania, 

 and we have only one observation in subtropical water south of Melbourne ; this was at 

 St. 896 in June 1932 when the surface content was 18 mg. In the same month off the 

 east coast of Tasmania at Sts. 897 and 898 subtropical surface water had a content of 

 26 mg. which increased to 33 mg. just south of the island. 



In subtropical water west of North Island, New Zealand, in early June 1932 the 

 surface phosphate content was of the order 28-32 mg. (Sts. 925-928). East of North 

 Island, New Zealand, there is only one observation which was made in late January 1934 

 when the surface content was only 10 mg. at St. 1281. Owing to the low latitude of the 

 subtropical convergence in the central and eastern parts of the South Pacific Ocean 

 there are no phosphate observations available in this zone, although it is certain that 

 off the west coast of South America considerable quantities of phosphate must exist in 

 the surface layer in this zone in order to maintain the very large concentrations of plankton 

 which are known to be present. 



It is difficult to summarize the distribution of phosphate content throughout the 

 subtropical zone owing to the relatively small number of observations which are 

 spread over several months of the year. However, it is possible to say that at the southern 

 end of the zone a minimal surface content of 5-10 mg. has been found in January, March 

 and April, whilst maximum phosphate seems to occur in the months of May, June, July, 

 August, September, and exceptionally in November, and to be greater than 30 mg.— 

 possibly as much as 50 mg. in some months. At the northern end of the zone we have 

 only figures for March and April when 5-10 mg. were found in the South Atlantic, but 

 in April 1935 in the western part of the South Indian Ocean the phosphate in the surface 

 layer at the northern end of the zone had been reduced to zero. The eastern part of 

 the South Atlantic Ocean has a greater surface phosphate content in this zone than has 

 the western half. 



In the South Atlantic Ocean very few observations of silicate content have been made 

 in the subtropical zone. In late November 1933 at the southern end of the zone, 

 south of Tristan da Cunha, the surface content was less than 300 mg. The eastern part 

 of the South Atlantic Ocean had a surface content of about 200 mg. throughout the 



zone in late March 1933. 



South of Cape Town in late March 1935 (Sts. 1554 and 1555, section 4, Plate VIII), 

 the silicate content of the surface water was less than 250 mg. from the station nearest 

 the coast to the subtropical convergence. In the second week of April 1932 (section 5, 



