An isotopic model for basal freeze‐on associated with subglacial upward flow of pore water

Abstract

Subglacial freezing in polar glaciers can have a significant dynamical effect. Recent studies have shown that freezing of pore water flowing upward through subglacial fine‐grained sediments at the freezing interface and progression of this freezing front downward are responsible for fast ice flow stoppage in ice streams. The upward pore water flow leads to the formation of debris‐bearing basal ice layers. A model for stable isotope composition, both in δD and δ18O, is developed for predicting the isotopic composition of the ice segregated by such a mechanism. The development of this isotopic model for water films present along the grains of the subglacial sediment predicts the absence of apparent fractionation for the ice formed. This prediction is tested against two East Antarctic outlet glaciers by studying the δD‐δ18O relationships in the basal ice layers of these glaciers.