Weertman regelation, multiple refreezing events and the isotopic evolution of the basal ice layer

A simple model is developed to simulate the isotopic fractionation which accompanies Weertman regelation at the bed of temperate-based glaciers. The fractionation equations of Jouzel and Souchez (1982) are applied to multiple refreezing events over measured glacier-bed profiles, and mass balance is maintained as the basal ice and meltwater produced at one bedrock hummock enter the next. Simulation results indicate that undeformed regelation ice layers are on the order of millimetres to centimetres thick, often being completely melted at the stoss face of certain hummocks and exceptionally reaching a thickness in excess of 10 cm. Neither the internal morphology nor the isotopic composition of these layers is constant, but both vary down-glacier in accordance with bedrock configuration. A glacier-wide fractionation process is identified whereby heavy isotopes are preferentially removed from the basal meltwater film and incorporated into the basal ice. This process might go some way to explaining the anomalously "light' isotopic composition measured in base-flow waters leaving some glaciers. Heavy isotope enrichment of this magnitude and consideration of the thickness of the basal ice layers concerned may explain the absence of recorded basalt ice samples heavy enough to have been formed in equilibrium with subglacial precipitates sampled at one of the sites (Glacier de Tsanfleuron) and reported in an earlier paper. -from Authors