In surface phytoplankton samples (layer between 0 and 1 m) taken with a sampler towed by RV Professor Vize, Corethron criophilus dominated over vast areas within the distribution of the south peripheral waters and the centre of the Weddell Gyre. In the eastern Weddell Gyre a great change in the composition of phytoplankton species was registered. Variability in phytoplankton species composition occurred mainly in the Antarctic Convergence Zone. A seasonal shift in species composition was observed in the same regions (sub-Antarctic waters, the Convergence Zone proper, south periphery of the Antarctic Circumpolar Current). A great change in phytoplankton composition was also found near the continent (Alasheev Bay). During the observation season maximum biomass values of surface phytoplankton were registered in the south periphery of the Antarctic Circumpolar Current.