EVIDENCE FOR REGIONAL CLIMATE-CHANGE IN THE RECENT EVOLUTION OF A HIGH-LATITUDE PRO-GLACIAL LAKE

Lake Wilson, a perennially ice-capped, deep (>100 m) lake at 80 degree s S in southern Victoria Land was investigated in January 1993. Water chemistry and physical structure showed three distinct layers; an uppe r c. 35 m mixed layer of low salinity, moderately turbid water; a less turbid mid layer, 20 m thick of slightly higher salinity and supersat urated with oxygen; and a deep 20 m brackish layer (conductivity c. 40 00 mu S cm(-1)) with anoxic conditions in the lower 5 m. Extreme super saturation of N2O (up to 400 times air saturation) together with high nitrate concentration (4000 mg m(-3)) was recorded in the deep layer. Phytoplankton biomass and photosynthetic activity was confined to the upper mixed layer and the band of supersaturated dissolved oxygen loca ted at 40-55 m appears to represent a relict layer from when the lake level was lower. The evidence from a comparison of profiles between 19 75 and 1993 suggests that Lake Wilson has risen 25 m since 1975, synch ronous with a period of lake level rise in the McMurdo Dry Valleys lak es to the north at 77 degrees S. Geochemical diffusion models indicate that Lake Wilson had evaporated to a smaller brine lake about 1000 yr s BP, which also fits the pattern shown by the McMurdo Dry Valleys lak es. Climate changes influencing lake levels have thus covered a wide a rea of southern Victoria Land.