320 DISCOVERY REPORTS 



The values are of the order of twice as great as those found in the oceanic Northern 

 Region. 



Table 9 



It will be seen that here the sudden onset of the main increase is well marked, and 

 that the peak period is reached in January, as is to be expected from the fact that the 

 area includes some more southerly waters than the oceanic Northern Region. These 

 observations are not sufficient to show whether the very slight secondary autumnal 

 increase indicated, after the profound post-maximal decrease, is a regular feature. 

 Some of our earlier work (Hart, 1934, p. 76) indicates that it may be quite considerable 

 locally, in some seasons. 



Qualitatively, the phytoplankton of the Scotia Sea shows populations intermediate 

 in character between that of the South Georgia area and the more northerly oceanic 

 regions, as one would expect. While the neritic ice-edge Group III diatom species — 

 particularly Thalassiosira spp. and Choetoceros sociale — are extremely abundant during 

 the main increase, members of the oceanic groups play a larger part than off South 

 Georgia. This applies especially to Nitzschia seriata of Group I, the Rliizosolenia spp. 

 in Group II and to Chaetoceros atlanticum of Group IV. Phaeocystis brucei may be 

 locally important where the area is invaded by pack-ice — not later than January as a 

 rule. In the autumn Group IV and Nitzschia seriata may be particularly prominent in 

 some seasons and, quite locally, Biddidphia striata, almost the only member of Group 

 III to develop in numbers later than the period of the main increase. 



The qualitative aspect of the phytoplankton in the Scotia Sea has already been very 

 fully treated in our previous work (Hart, 1934, pp. 69-88). Many of the estimations 

 used in the description of the quantitative cycle described here were obtained during 

 the fourth commission when I was serving elsewhere, so that there has not yet been 

 any opportunity to work them up qualitatively. In view of the considerable amount of 

 evidence already available it did not seem necessary to go further into the qualitative 

 aspect for the purpose of the present report. 



