42 DISCOVERY REPORTS 



ice-edge in 77 W, the surface value increased from 450 mg. in the north to 1950 mg. 

 at the ice-edge. In December 1933 the value decreased towards the north in 8o Q W 

 from a value 2100 mg. at the ice-edge to 900 mg. at the northern boundary of the zone. 

 In January 1934 the average ice-edge value across the South Pacific was 2050 mg., 

 and the average of all stations within 250 miles of the ice-edge was 1700 mg. The ice- 

 edge content in the extreme east was of the order of 2000 mg. and between 86° and 

 109 W it fell below 1000 mg. ; west of 109 W it increased again to over 2000 mg. The 

 position in which the surface content fell below 1000 mg. appears to be related to a bending 

 of the surface current towards the south. 1 In late January 1934 a line of observations from 

 the eastern entrance to the Ross Sea in 69!° S, 159F W towards New Zealand showed 

 that at the southern end the surface content was 2600 mg., a value which increased to 

 3200 mg. in 65 05' S, 166 08' W. This value was the only example in the South Pacific 

 of a surface content of such a high order. North of this extremely high value the content 

 fell rapidly, so that at St. 1273 in 62 08-1' S, 169 59-9' W there were less than 200 mg. 

 of silicate in the surface. It may be added that the position of St. 1273 is well south of 

 the Antarctic convergence, and the great disparity between the surface content at this 

 position and that found a short distance farther south shows very clearly how the 

 concentration of a nutrient salt can vary very considerably over a short distance in the 

 Antarctic zone. 



In late January 1935 the silicate contents at stations in the Scotia Sea showed that 

 phytoplankton had reduced the amount present. Thus the surface content near the 

 South Orkney Islands was only 650 mg., and this value diminished northwards so that 

 just south of the Antarctic convergence less than 300 mg. were present. 



In a survey around South Georgia with an average date of 3 February 1935, the 

 average surface value was 750 mg., whereas we have seen that in the previous week the 

 Scotia Sea content was 650 mg. near the South Orkneys, and less than 300 mg. in the 

 north. A comparison of these figures suggests that there is always more silicate available 

 around South Georgia than in the open sea. 



In mid-February 1935 the average silicate content found in the surface during a cruise 

 from a position just south of the South Sandwich Islands to the ice-edge at the eastern 

 entrance to the Weddell Sea and along the ice-edge to 42F E, was 2650 mg. for 

 eighteen stations ; the content at the ice-edge averaged 2950 mg. The average contents 

 were lowered by the values at some stations with large phytoplankton concentrations 

 and by those of a " grazed down" area east of 30° E. Probable ice-edge figures for the 

 South Atlantic are of the order 3000-3500 mg. before the main phytoplankton outburst. 

 In early March 1935 at 42^° E the ice-edge surface value was 2700 mg., a value which 

 decreased towards the north until just south of the Antarctic convergence the content 

 was 1000 mg. In mid-March 1933 the ice-edge value was 2700 mg. at 69 30' S, 

 9 34' E, and this also decreased towards the north to 2000 mg. some 250 miles south 

 of the convergence. 



1 Deacon, 1937, p. 38. 



