PHYTOPLANKTON OF SOUTH GEORGIA 



43 



The main features of the phytoplankton on this Hne are well brought out in the table. 

 As will be seen later, the general character of the phytoplankton, which as compared 

 with some others on this survey was rather poor in species and rich in individuals, par- 

 ticularly of the larger forms, all tends to show that the origin of the surface water was in 

 the eastern Weddell Sea, except at the anomalous St. 493. The eastern Weddell Sea 

 influence was almost certainly strongest at Sts. 496, 495 and 494, where a relatively high 

 proportion of Rhizosolenia styliformis was observed. At the others the water was com- 

 paratively old, and at the inshore stations it is probable that considerable mixing had 

 taken place. There seems to be a sort of eddy off the north-east coast of South Georgia 

 at about this point where the surface water is checked in its normal northerly flow and 

 develops a phytoplankton of a type characteristic of old mixed water although there may 

 be comparatively "young" eastern Weddell Sea water to the north-east. 



The striking difi^erence in the character of the phytoplankton at St. 493 is well illus- 

 trated by the volumes of the catches (Table IX). It will be seen that the volumes ex- 

 ceeded 250 cc. at all the other stations on the line, but at this one the volume was only 

 60 cc. With small forms dominant the estimated total reached 40 millions, however, so 

 that we have here a good example of the unreliability of volumes as a guide to the 

 quantity of phytoplankton, whenever the quality is liable to abrupt changes. 



The general character of the phytoplankton taken on the Prince Olaf line (Fig. 4) 



seems to indicate a development from comparatively old water of the eastern Weddell 



Sea type, with possibly a considerable degree of mixing from old Bellingshausen water 



from the west, especially towards the middle and outer end of the line. The numbers 



and percentages of the leading forms are shown in Table 6 ; the full analyses will be 



found in Table X. 



Table 6 



From this table it will be seen that at the two inshore stations Corethron valdiviae was 

 strongly dominant, with a moderate proportion of Thalassiosira antarctica at St. 485 as 

 the only other form of much importance. At the next two stations seaward Corethron 

 was not encountered in anything approaching these numbers. Chaetoceros criophilum 



6-2 



