ANTARCTIC SURFACE WATER 



33 



there are three observations south of the convergence which are shown below. The 

 silicate values are those for the surface and lower part of the Antarctic surface layer. 



The values in the above table show that during the summer a very large proportion 

 of the available silicate is utilized by the phytoplankton. In this connexion it should 

 be noted that the value of <30o mg. in late January was obtained at a time considerably 

 later than the date of the maximum concentration of the phytoplankton, and it is possible 

 that in mid-December in this position the surface silicate content was even less than 

 that recorded in late January. The value of 1050 mg. was obtained immediately prior 

 to the time of the main outburst of phytoplankton. 



Thus, just south of the Antarctic convergence in the Scotia Sea, the surface silicate 

 content in 1935 was reduced during the phytoplankton season from a pre-outburst value 

 of the order of 1050 mg. to probably well under 300 mg., a utilization of at least 75 per 

 cent of the available silicate. The concentration of phytoplankton which the Scotia Sea 

 supports is, of course, very high. 



Outside the Scotia Sea near the Antarctic convergence in 22° W a surface value of 

 H5omg. was recorded in Antarctic water in late August 1934 at St. 1390, 51 30-5' S, 

 22 14-6' W. The order of this value compares with the surface content just south of 

 the convergence in the Scotia Sea previous to the main phytoplankton outburst. 



South of the Antarctic convergence north of Enderby Land the surface silicate varied 

 considerably from year to year as the following results show : 



Sts. 850, 1 1 60 and 1560 were situated immediately to the north of the cold easterly 

 current which flows across the South Atlantic from the Weddell Sea; this current 

 appears to have a high silicate content at the surface. It is possible that in the early 

 autumn months of 1932 and 1933 the water at Sts. 850 and 1160 was more influenced 

 by the Weddell Sea current than in April 1935 at St. 1560, or else, owing to a difference 

 in time of the phytoplankton outburst in the different years, regeneration began earlier 

 in 1932 and 1933 than in 1935. On the other hand, values of surface silicate content 



