EVIDENCE FOR PHYSICAL AND CHEMICAL STRATIFICATION IN LAKE-UNTERSEE (CENTRAL DRONNING MAUD LAND, EAST ANTARCTICA)

Lake Untersee is the largest freshwater lake in the interior of East A ntarctica. It is a perennially ice-covered, max. 169 m deep, ultra-oli gotrophic lake. In contrast to earlier studies, we found clear evidenc e for physical and chemical stratification in the summer of 1991-92. H owever, the stratification was restricted to a trough, c. 500 m wide a nd up to 105 m deep, in the south-western part of the lake. There, the water body was distinctly stratified as indicated by sharp vertical g radients of temperature, pH, dissolved oxygen, and electrical conducti vity. The water column was anoxic below 80 m. The chemical stratificat ion is also indicated by changes of ionic ratios. Moreover, there was some evidence for methanogenesis and bacterial sulphate reduction in L ake Untersee.