BOTTOMWATER FORMATION DUE TO HYDROTHERMAL ACTIVITY IN FROLIKHA-BAY, LAKE-BAIKAL, EASTERN SIBERIA

Hydrothermal water enters Frolikha Bay, a well-known site of high geot hermal heat flux in the northern part of Lake Baikal, at 400 m depth. On the basis of CTD profiles, the hydrothermal water is identified as forming an anomalous bottom layer with a higher temperature (> 0.15 de grees C) and salinity (> 2.5 mg . kg(-1)) than the overlying water. Du e to the entrainment of lake water, a distinct dense water layer up to 40 m thick, stabilised by its slightly higher salinity, becomes estab lished close to the bottom of the bay. The density current thus genera ted flows out of the bay towards the deeper parts of the basin. Since helium isotope analysis shows that the geochemical characteristics of the hydrothermal water are similar to those of water from nearby hot s prings on land, the bottomwater of Frolikha Bay is easily interpreted in terms of the mixing of ordinary fresh water from the lake and hydro thermal water carrying isotopically heavy He from the continental crus t. Because of its high crustal He content, a similar hydrothermal comp onent may even be identified in the open water of the northern basin.