APPENDIX I. ON FACTORS LIMITING PHYTO- 

 PLANKTON PRODUCTION IN EAST CUMBERLAND 



BAY, SOUTH GEORGIA 



(Text-figs. 80-4) 



INTRODUCTION 



The aim of this work was to endeavour to determine the factors Umiting phytoplankton 

 production throughout the season in the inshore waters round South Georgia, and, if 

 possible, to keep sufficient check on the inshore conditions to permit of some com- 

 parison being made with those obtaining offshore. 



The great difficulty in the interpretation of phytoplankton periodicity in the south 

 lies in the fact that there appears to be a superabundance of nutrient salts, even at the 

 surface layer, at all seasons. Particular attention was given, therefore, to other factors 

 that might prove to be limiting ; but as the locality investigated was an inshore one, it 

 was felt that some check should be kept upon the amount of nutrient materials present. 

 Samples from all the depths worked were analysed for phosphate but, owing to pressure 

 of other work, it was impossible to attempt the analysis for nitrate as well. Gran (1929) 

 has emphasized the possible importance of land drainage as a source of nutrient 

 materials in the northern hemisphere, but later workers have shown that it is probably 

 not so important a factor as was at first supposed. Owing to the relatively cold summer 

 climate, and the singular barrenness and inconsiderable extent of the land in the lati- 

 tudes in question, it would seem that this factor does not operate in the south. 



A station was chosen in the deep water in the middle of the bay {ca. 90 fathoms) at 

 which good cross-bearings could be obtained, and routine observations were carried out, 

 as nearly as possible at weekly intervals, from November 12, 1930, to March 29, ig^i. 

 At each station water samples were taken with a Nansen-Pettersen bottle at depths of 

 o, 5, 10, 20, 30, 40, 50 and 75 m. These were analysed for salinity, hydrogen-ion con- 

 centration, and phosphate and oxygen content by the standard methods employed in 

 the expedition. The analyses for phosphate content and hydrogen-ion concentration 

 were always carried out within twenty-four hours of the completion of each station. 



At the outset it was hoped to investigate the phytoplankton by the centrifuge method. 

 Unfortunately the inshore plankton proved so scanty that this was impossible, and it 

 was necessary to rely on two hauls with the Gran \ m. vertical net (N 50 V), from 

 25 to o, and from 50 to o m. The samples were estimated by the usual Hensen methods. 



We were very fortunate in having the use of the motor-boat ' Alert ', a powerful, 

 beamy, decked-in craft, 25 ft. long over all, and ideally suited to the work in hand. 

 Thanks to her seaworthy qualities we were able to work on one or two occasions towards 

 the end of the season in conditions previously thought impossible. In high winds drift 

 was excessive owing to the very considerable freeboard of the boat, but it was still 



