SUB-ANTARCTIC WATER 59 



1 934. In September 1932 the silicate content in sub-Antarctic water increased from 310 mg. 

 close to Wellington, New Zealand, to 570 mg. at the southern end of the zone. In late 

 January 1934 the surface content was less than 200 mg. everywhere in the zone; indeed ) 

 it was even less than 200 mg. in the northern part of the Antarctic zone. The summer 

 values of January 1934 indicate that the main phytoplankton outburst had removed all 

 but a very small amount of silicate some time previously, as there was a very poor 

 concentration of phytoplankton present at the time the silicate observations were 

 made. 



In the course of the W-shaped cruise (sections 12, 14, 15, 16) across the South Pacific 

 Ocean in mid-September to early October 1932, the subtropical convergence was not 

 crossed, but in sub-Antarctic water the silicate content of the surface decreased from a 

 value of 450 mg. at 54 02-8' S, 142 25-4' W near the southern boundary of the zone 

 to 200 mg. in 41° 03-1' S, 126 03-9' W, a position some distance south of the sub- 

 tropical convergence. Farther east at St. 976 in 59 22' S, 89 03-9' W at the southern 

 end of the zone the silicate content of the surface was 720 mg., a value which decreased 

 to 470 mg. at 55 18-4' S, 8o° 08-1' W in early October 1932. 



At 8o° W there are five sets of observations in the southern part of the zone, the most 

 northerly of these being in 55 11-3' S. In late December 1933 (Sts. 1225-1229), the 

 surface content decreased northwards from 750 to 200 mg. ; in March 1934 at Sts. 1317- 

 1320 the silicate had been reduced to zero at the southern end of the zone, increasing, 

 probably by regeneration in situ, a short distance farther north to a value of 450 mg. 

 only to fall again to zero throughout the remainder of the section which finished in 

 55f° S; in mid-September 1934 at Sts. 1417-1421 the surface value was greatest of all, 

 the contents ranging from 850 mg. at the southern end of the zone to zero in 55 22' S ; 

 in late October 1934 at Sts. 1441-1446 the surface content was as high as 550 mg. at 

 the northern end of the section in 55 39' S increasing to 800 mg. at the southern end 

 of the zone. The fact that the surface value was zero at 55 22' S in September and 

 as much as 550 mg. in a position a few miles away 41 days later must be due to the 

 presence of water of low silicate content coming from the north in September. 



The discussion of the surface phosphate content of sub-Antarctic water shows that 

 only a tentative summary can be made. Similarly the silicate data show that many 

 more observations are needed before an accurate picture can be obtained either of the 

 distribution or of the seasonal variation in this zone. In winter the southern part of the 

 sub- Antarctic zone has a surface content of about 700 mg., the eastern part of the 

 South Pacific Ocean having perhaps a slightly greater content. The northern end of 

 the zone has an approximate content of 0-300 mg. in winter. Summer values for the 

 southern and northern parts of the zone are of the order of less than 200 mg. and 

 between zero and less than 200 mg. respectively. 



8-2 



