i6 



DISCOVERY REPORTS 



ANTARCTIC SURFACE WATER 

 PHOSPHATE CONTENT AT THE SURFACE 



In the introduction to this report we saw that as far as the phytoplankton is concerned 

 two very different regions exist in the Antarctic zone. One, the northern region, where 

 the phytoplankton production is enormous and is confined to a relatively brief period 

 of growth and decline, and the second in the southern region, where the production is 

 far less in actual concentration but is spread over a longer period. With these facts in 

 mind we will review the phosphate and silicate contents of the surface water in both the 

 southern and northern regions of the Antarctic zone. The data are presented as surface 

 values and later as mean integral averages of the o-ioo m. layer to satisfy both the biological 

 and hydrological requirements. The photosynthetic layer of the Antarctic surface water 

 is usually a very shallow layer ; under ideal conditions it consists of a well-illuminated, 

 shallow layer separated from the rest of the surface layer by a strong discontinuity. 

 Consequently surface values of nutrient salt content are of more importance to the 

 planktologist than o-ioo m. averages. On the other hand, the o-ioo m. averages offer 

 a good picture of the nutrient salt content of the surface layer in the Antarctic zone. 



During a cruise across the Southern Ocean south of the South Atlantic Ocean and 

 as far east as 44 E, mainly in the second half of February 1935, the surface phosphate 

 values were as shown in Table I. 



Table I 



Denotes ice-edge station. 



