ANTARCTIC SURFACE WATER 43 



In late March 1934 the western part of the Scotia Sea had a surface content of i5oomg. 

 which decreased to 850 mg. at the northern boundary of the Antarctic zone. 



In the South Pacific Ocean in March 1934 fifteen stations within 250 miles of the 

 ice-edge gave an average value of 1550 mg., with an average of 1750 mg. at the actual 

 ice-edge. A smaller silicate content was again found between 86° and 1 io° W. At 8o° W 

 in March 1934 the surface value dropped from 1750 mg. at the ice-edge to less than 

 300 mg. at the Antarctic convergence. 



In early April 1934 the surface content in the middle of the Scotia Sea varied from 

 3050 mg. close to the South Orkney Islands to 350 mg. just south of the convergence. 

 In late April 1934, outside the Scotia Sea, some observations made just east of the South 

 Sandwich Islands showed that the surface silicate slowly increased southwards from less 

 than 300 to 1 100 mg. and then jumped to 3050 mg. at the most southerly station in 

 6*° J 9'5' S, 2I ° 39' l ' W. This line of observations was interesting because the surface 

 water at all stations except the most southerly had passed through the Scotia Sea and 

 across the ridge between South Georgia and the South Sandwich Islands, losing silicate 

 by phytoplankton activity in the crossing. The high content at the most southerly 

 station was due to the station being made in Weddell Sea water which has a very 

 high silicate content. The surface content of 3050 mg. corresponded exactly with that 

 measured a few days earlier close to the South Orkneys. 



In mid-April 1932 in the Antarctic zone between the longitude of Cape Town and 

 Enderby Land the surface silicate increased southwards from 2400 to 3400 mg. at the 

 ice-edge. 



In May 1934 between 58^° S, 16 E and the ice-edge in 45 E, the surface silicate fell 

 southwards from 2700 mg. to the order of 1500 2000 mg. and then increased to about 

 2000-2500 mg. near the ice-edge. The fact that the content fell to a value of 1500- 

 2000 mg. was probably due to a large concentration of phytoplankton having consumed 

 the nutrient salts previous to the time of our observations. It will be remembered that 

 in February 1935 we came upon strong evidence for a large concentration of phyto- 

 plankton near this position. Between the ice-edge in 45 E and the region just south 

 of the Antarctic convergence near the Crozets, in May 1934, the surface content fell 

 from 2200 to 850 mg. 



In late May 1932, south of Australia, the silicate content in the Antarctic zone 

 increased southwards from a value of 450 to 2700 mg. at the ice-edge north of Adelie 

 Land. 



There are no observations for June and July, but in late August 1934 the surface 

 value at 55 S, 20 W was 2050 mg., a value which decreased towards the north-west 

 until just south of the convergence it was 11 50 mg. Around South Georgia, which is 

 about 250 miles south of the convergence, an average value at twelve stations in late 

 August 1934 was 1750 mg. 



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