The limnophysics and limnochemistry of high mountain lakes in the Tyrolean Alps (Austria) have been of particular interest since the earliest limnological investigations in this region (e.g. STEINBOCK 1934, LEUTELT-KlrKE 1934, 1935, ErrACHER 1966, PECHLANER 1967). Gossenkõllesee (2,413 m a.s.l.; 47" 13' N, 11 o 00' E), a clear water lake situated well above the timberline in the crystalline Stubai Alps (Tyrol, Austria), has attracted special attention. At Gossenkõllesee STEINBOCK (1934) proved the existence of a thermocline in high mountain lakes. Furthermore, during the winter, LEUTELT-KlPKE (1934, 1935) detected in Gossenkõllesee an oxygen supersaturation of 136% just beneath its ice cover whereas oxygen was depleted down to 31% saturation in the bottom waters. LEUTELT-KlPKE (1935) described this pattern to be somehow contradictory to the oligotrophic status of Gossenkõllesee and defined it as an oligotrophic lake with a "winter pseudoeutrophy". The contemporary studies at Gossenkõllesee on atmospheric precipitation, snow chemistry and biogeochemistry of the lake and its inlets (e.g. NICKUS et al. 1998, THIES et al. 1998, this study) rely on the existence of a modern research station situated at the lake shore. The lake and its catchment are situated within a UNESCO Biosphere Reserve which was designated in 1977.