ANTARCTIC SURFACE WATER 



55 



from the ice-edge to far north as 63 1° S in all the months examined. In March this 

 rapid fall was of the order of 1850 mg. and in the other months 550-1200 mg. In March 

 the extent of the fall is exaggerated by the presence of sub-Antarctic water of low 

 silicate content in the 0-60 m. layer at Sts. 13 15 and 13 16. When the narrow width of 

 the Antarctic zone in 8o° W is considered the silicate gradient across the zone is very 

 steep. 



LATITUDE 



STATION '- 



A.C. 



OEcisJ. 



ffltVJ 





r 





tyt oj i\j 



• DECEMBER 1933 



© MARCH 



X SEPTEMBER Lg34 



A OCTOBER 



■ NOVEMBER J 



Fig. 17. The mean integral average silicate content of the 0-100 m. layer in 8o° W. 

 It is safe to assume that the average silicate content of the 0-100 m. layer in February 

 1934 at about 66° S was of the order of 1 100 mg., and, as we know that in October it was 

 2000 mg., we may conclude that a minimum net withdrawal of 45 per cent of the available 

 silicate content took place at this latitude. It is impossible to give even an estimate of 

 the consumption at the Antarctic convergence until observations are made in January 

 and more in March. 



SUB-ANTARCTIC SURFACE WATER 

 PHOSPHATE AND SILICATE CONTENTS AT THE SURFACE 



Owing to the fact that the majority of the observations by the ships of the Discovery 

 Committee has been made in Antarctic waters, there is not sufficient evidence to give a 

 complete account of the seasonal variation in the nutrient salt content of the surface 

 water in the sub-Antarctic zone. The data that are available were collected chiefly during 

 the circumpolar cruise of R.R.S. 'Discovery II' in 1932. We have more data at the 

 southern end of the zone than just south of the subtropical convergence. 



