Dielectric signatures and evolution of glacier ice

Abstract

AbstractWe analyzed the dielectric spectra (0.1 Hz–1 MHz) of 49 firn and ice samples from ice sheets and glaciers to better understand how differing ice formation and evolution affect electrical properties. The dielectric relaxation of ice is well known and its characteristic frequency increases with the concentration of soluble impurities in the ice lattice. We found that meteoric ice and firn generally possess two such relaxations, indicating distinct crystal populations or zonation. Typically, one population is consistent with that of relatively pure ice, and the other is significantly more impure. However, high temperatures (e.g. temperate ice), long residence times (e.g. ancient ice from Mullins Glacier, Antarctica) or anomalously high impurity concentrations favor the development of a single relaxation. These relationships suggest that annealing causes two dielectrically distinct populations to merge into one population. The dielectric response of temperate ice samples indicates increasing purity with increasing depth, suggesting ongoing rejection of impurities from the lattice. Separately, subglacially (lake) frozen samples from the Vostok (Antarctica) 5G ice core possess a single relaxation whose variable characteristic frequency likely reflects the composition of the source water. We conclude that multi-frequency methods are essential to dielectric discrimination between different types of glacier ice.