ANTARCTIC SURFACE WATER 4 , 



from 800 to 1400 mg. in the west and from 850 to 1150 mg. in the eastern part. In late 

 September 1934 the stations in the Antarctic zone between the Falkland Islands and 

 Elephant Island had a surface silicate content of 900 mg. in the north and of 1400 mg. 

 in the south. 



In October the data are still very meagre ; between South Georgia and the Falklands 

 the surface silicate content in the Antarctic zone in the second week of October 1934 

 varied from about 1050 mg. in the east to 750 mg. in the west, whilst a few days earlier 

 a value of 1250 mg. was obtained some 180 miles north of the South Orkneys. In 8o° W 

 the ice-edge had retreated at the end of October 1934 some 140 miles from the position 

 in the second week of September, to a latitude where the silicate content at the surface 

 was 2000 mg. in place of 11 50 mg. in September. The northern boundary of the zone 

 in 8o° W had a surface value of 1150 mg., the same as it September. 



In early November 1934 some fourteen stations between 59i°-66^° S and 8o°-i io° W 

 gave an average surface value of 1250 mg., whilst those actually at the ice-edge had an 

 average content of 1575 mg. A few days later in 8o° W the ice-edge surface content was 

 1475 mg., and at the northern boundary 1050 mg. was recorded. At a number of 

 stations near South Georgia at the end of November 1933 the average surface figure 

 was 650 mg. at a time when enormous catches of phytoplankton were being made, so that 

 peak conditions for the withdrawal of silicate from the surface layer were prevailing. 

 Owing to upwelling and turbulent mixing in the vicinity of South Georgia it is likely 

 that the photosynthetic layer around the island will always have more silicate present 

 than in the open ocean at the same distance from the Antarctic convergence. This follows 

 from the results of the survey at South Georgia in November 1933 when even with the 

 enormous concentrations of phytoplankton present, probably the heaviest in the world, 

 there was still an average of over 650 mg. remaining in the surface (see footnote p. 112). 

 At St. 1 198, which was situated close to the northern boundary of the Antarctic Zone 

 and was made immediately previous to the November 1933 survey at South Georgia, 

 the surface value was o mg. ; a heavy concentration of phytoplankton was present. This 

 would seem to indicate that at the time of the peak concentrations of phytoplankton the 

 silicate content of the surface may be reduced to zero, and that if it were not for up- 

 welling and turbulent mixing at South Georgia the silicate content around the island 

 might be completely utilized in the photosynthetic layer. The actual concentration of 

 phytoplankton around South Georgia in November 1933 was more than i| times 

 greater than at St. 1198. 



In December our data are confined to parts of the Scotia Sea and to 8o° W. In 

 December 1933 the surface content 60-70 miles north-east of South Georgia was 

 500 mg. ; this value increased to the south-west of the island. North-east of South 

 Georgia a very heavy toll had been taken by the phytoplankton. South-west of the 

 island the observations were made at places close to the line of pack-ice which is usually 

 present in the early part of the season near the Shetland-Orkney ridge, and the surface 

 value here was over 2000 mg., whilst at the ice-edge in 8o° W a value of 2100 mg. was 

 found. In late December 1933, in the Antarctic zone between the Falklands and the 



