apparently more correctly be considered to be not the Antarctic divergence 

 (Kozlova, 1964), but rather the northern limit of the icepack. 



Many authors have affirmed the relatively low quantities of 

 phytoplankton in the Subantarctic zone in comparison to the Antarctic 

 (Boden, 1949; Beklemishev, 1960; Kozlova, 1964; El-Sayed, 1970a). However, 

 some data indicate that inverse quantitative relationships do exist 

 (Hart, 1934; Cassie, 1963; Hasle, 1969; Steyaert, 1973). The quantity 

 of algae during the peak period in the Subantarctic can reach the same 

 order of magnitude as in the lower Antarctic. The opinion of the poorness 

 of the Subantarctic has resulted apart from the fact that this area is 

 usually explored by expeditions which have come in to study the Antarctic 

 summer, and they crossed this zone after the phytoplankton bloom; compari- 

 sons have been conducted for waters in different stages of plankton suc- 

 cession. 



The data presented reflect the differences in the individual water 

 areas only in terms of the quantity of phytoplankton during the period 

 of abundance. Productivity estimates might be essentially different, 

 first of all due to the different duration of the vegetation season. 

 Attempts to determine this quantity approximately on the basis of the 

 data presented by Hart (1942) on the mean annual quantity of plant 

 pigments show that the southern zone is 207o poorer, the northern zone 

 20% richer, than the intermediate zone. The inshore waters of South 

 Georgia are four times more productive than the northern zone, within 

 which this island lies. 



Composition of flora and its seasonal changes . The flora of the 

 Southern Ocean has been studied quite insufficiently. At the present 

 time, some 180 taxons of diatoms, 70 species of dynoflagel lates, five 

 coccolithins and five sil icoflagel lates have been listed (Hasle, 1969). 

 We can use the data of Hasle (1959), who has considered the area of dis- 

 tribution of 77 species (in addition to the broadly distributed species) 

 to judge the degree of isolation of the flora of individual zones. Among 

 the species she studied, the number found in the Antarctic and Subantarctic 

 is practically the same; 30% of the species inhabit the Antarctic alone; 

 some 27% of the species are not seen in the Antarctic; all of them, 

 except for one Subantarctic endemic species, being invaders from the 

 northern waters. The low degree of endemism of the Subantarctic flora in 

 comparison to the Antarctic also follows from analysis of the distribution 

 of dynoflagellates (Balech, 1968). 



A predominant role of diatoms is characteristic for the Southern 

 Ocean. Their number in the Subantarctic represents up to 80%, in the 

 Antarctic up to 99.9% of the species present (Hart, 1934). The composition 

 of phytoplankton is quite uniform: Almost always (96% of cases), one 

 or two species make up more than half of the total population (Marumo, 

 1953). Among the dominant species are: in the Subantarctic, Chaetoceros 

 neglectus , Nitzschia " barkleyi ," Coccol ithus h uxleyi , in the lower 

 Antarctic--Ch^. dichaeta , Ch . neglectus , Fragi lariopsis " nana ," N^. 

 closterioides , in the higher Antarctic--F. curta , £. cyl indrus , and H_. 

 subcurvata . The variety index of flora Tafter Margalef) is not great, 

 increasing from 2.4-3.0 in the southern zone of the Antarctic to 3.2-3.7 

 in the Subantarctic (Hasle, 1959). 



