GEOCHEMISTRY OF SUBGLACIAL CALCITES - IMPLICATIONS FOR THE HYDROLOGY OF THE BASAL WATER FILM

Three types of calcite precipitate are found in the proglacial area of the Glacier de Tsanfleuron, Switzerland. Sparite and micrite form part of an evolutionary series precipitated in response to solute concentration as a result of progressive freezing of the subglacial water film. Sparite forms under open-system conditions or during the early stages of freezing under closed-system conditions, while micrite forms during the final stages of closed-system freezing. The origin of white deposits is less well understood. These could be explained by precipitation of calcite in equilibrium with atmospheric CO2 or as a result of fractionation due to photosynthetic removal of 12C from the water by cyanobacteria. In either case, formation in submarginal cavities where there is free access to light and to the atmosphere may be favored. -from Authors