PHYTOPLANKTON AND HYDROLOGY 



85 



Allen (1928) and Moberg (1928) have shown how the upwelling of phosphates and 

 nitrates against the coast of South California can give rise to a zone of rich phytoplankton, 

 but we have seen that such cannot be the explanation of such zones against the coasts 

 of South Georgia. One may speculate whether this rich phytoplankton is caused by 

 some other factor present in the upwelling water — other salts or the resting spores of 

 diatoms themselves — or again whether it is due, as Gran (1931) has recently shown can 

 sometimes be the case, to organic iron compounds carried out from the land. At present, 



Table XV 



Phytoplankton, phosphate and oxygen content, South Georgia survey, 

 December-January 1926-7, line F 



however, we must admit that we have no definite evidence of the cause, and this is one 

 of the important problems upon which it is hoped future work will throw light. It may 

 be found on different occasions to be due to different causes, and I would draw attention 

 to the following points which might form the basis of a further working hypothesis. 

 Not only is it seen that the pattern of phytoplankton production round South Georgia 

 corresponds remarkably well with that of phosphate consumption, but on comparing 

 Figs. 38 and 40 with Fig. 6 it is seen that the areas of denser production correspond with 

 those areas shown by Mr Clowes in his water-movement chart to be the areas of mixing 

 of the two water systems. In the preliminary account of the expedition in the Geo- 

 graphical Journal (1928) already referred to, I showed a chart of the production of 

 phytoplankton in the region of the South Shetlands measured in volumes— measure- 



