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The ice-free area around Ablation Point (70° 49' S, 68° 25' W) is of particular limnological interest. Numerous ponds and pools lie on coastal moraines and large, permanently ice-covered lakes lie in the valleys. Two of the lakes are unusual in that they are in contact with seawater from George VI Sound which is covered by an ice shelf, 100-500 m thick, and which separates Alexander Island from the Antarctic mainland. Evidence for the existence of a marine biome, 100 km from the open sea, was obtained from one lake. Freshwater biological samples added new genera to Antarctic lists, extended the known range of species, and illustrated the important role of isolation in the determination of antarctic biocoeneses.

Data on phytoplankton and zooplankton biomass, and physical and chemical variables, are combined with a published multivariate description of diatom species composition to interpret variation within an area around South Georgia surveyed during an austral summer. Large-scale species distributions could be equated to the different water masses which reflected the interaction of the Antarctic Circumpolar Current with the island and the Scotia Ridge. Small-scale factors were found to act at an interstation scale and imposed local variation on the biogeographic pattern. Nutrient depletion could be related to phytoplankton biomass hut no single inorganic nutrient of those measured (NO 3-N, PO 4-P and silica) could be identified as important. The ratio Si: P appeared to be more important as an ecological factor. The impact of grazing by krill and other zooplankton could only be resolved as differences in phytoplankton biomass and phaeopigment content. Diatom species composition showed a relation to local krill abundance very different from that suggested by published studies, but could be explained as the effect of earlier grazing outside the study area. The effects of vertical mixing could not account for interstation differences as pycnocline depth was uniformly greater than euphoric depth, and vertical stability very low. Some comparison was made with data collected in 1926-31 by the Discovery Investigations. Significant differences in the distribution of certain taxa such as Chaetoceros criophilum and C. socialis were traced to maj or differences in hydrology.