DISCOVERY REPORTS 



upper part of the water column consists of sub-Antarctic water, a much thicker layer 

 than the Antarctic surface water and including a subsurface current and the Antarctic 

 intermediate current. Below this there is the warm deep water which in turn overlies 

 the Antarctic bottom water which flows to the north. 



90E 



Fig. 3. Positions of stations where observations for phosphate or silicate were made in the sector of the 



Southern Ocean south of South Africa. 



In general the north and south circulation of the various waters of the Southern Ocean 

 are very similar to the South Atlantic circulation which is shown in Fig. 6. 1 



Amongst the nutrient salts utilized in the life-economy of the plankton, more par- 

 ticularly by the phytoplankton, are those of phosphate and silicate. Of the form in 

 which these salts exist in the ocean very little is known, and at present we shall deal 

 only with the amount of nutrient salt available for the metabolism of the plankton. 



It seemed to me that a very close relationship must exist between the phytoplankton 

 of the Southern Ocean and the amount of phosphate and silicate present, and that any 



1 This figure is taken from Deacon (1937), Discovery Reports, xv, p. 4. 



