INTRODUCTION 7 



discussion of the content of these salts in the sea must necessarily involve some concep- 

 tions of the distribution of phytoplankton and a brief resume of the waxing and waning 

 of the enormous concentrations found in spring and summer in the Antarctic. Dr 

 T. J. Hart informs me that within the Antarctic zone it is possible to distinguish three 

 areas characterized by the type of phytoplankton communities they support, and, broadly 



Fig. 4. Positions of stations where observations for phosphate or silicate were made in the sector of the 

 Southern Ocean south of Australia and New Zealand. 



speaking, by their geographical relation to the Antarctic convergence and to the ice- 

 edge. This distinction is necessarily less clearly defined where geographical features lead 

 to any marked difference from the average latitude of the convergence, as for instance 

 in the eastern South Pacific Ocean. The three areas are: a northern region extending 

 some 300 miles south of the Antarctic convergence, a southern region extending some 

 200 miles north of the ice-edge, and a rather less definite intermediate zone within which 

 our observations are not yet sufficiently numerous to permit any average extent being 

 determined. These limits are to some extent arbitrary, as the latitude of the Antarctic 



