The composition of basal ice from a glacier sliding over limestones

Samples of ice from the Tsanfleuron Glacier (Switzerland) were analyzed for Ca, Mg, Na, and K by atomic absorption. The basal ice is distinctly richer in Ca and Mg but slightly poorer in Na and K than the overlying glacier ice. The relative enrichment of Ca and Mg in basal ice appears to result from the limited incorporation of solutes as the ice forms by refreezing of pressure meltwaters that have flowed in intimate contact with the carbonate bedrock underlying the glacier. Because the bulk of the solutes are selectively rejected by the growing ice, they tend to accumulate in freezing subglacial waters until they eventually precipitate in areas where basal freezing is localized. This subglacial precipitation of CaCO3 results in thin superficial coatings of calcite that are abundant and particularly well developed in small concavities of the bedrock surfaces recently exposed by the retreat of the Tsanfleuron Glacier. Calculated minimum solute concentrations required to maintain such CaCO3 precipitation used in conjunction with an experimentally determined effective distribution coefficient, which characterizes the solute partitioning during the growth, can yield estimates of the Ca content of the regelation ice. The close agreement obtained between predicted and measured Ca contents in basal ice strongly supports the hypothesis that ice layers at the base of the Tsanfleuron Glacier are formed, at least in part, by regelation and that the calcite deposits result from the selective solute rejection that accompanies basal ice growth. © 1978 Geological Society of America.