Electrical resistivity sounding of the East Antarctic Ice Sheet

Abstract

Electrical resistivity soundings using a Schlumberger array have been carried out at Dome C, East Antarctica (74°39′S, 124°10′E, elevation 3400 m), to sound the entire 3500‐m depth of the ice sheet. Changes in density and temperature are largely separated in the ice at Dome C, so activation energies for both firn and ice could be determined: we find an activation energy of 0.25 eV in both solid ice and firn between −15°C and −58°C. A common value of the activation energy points to a single transport regime in which the charge carriers and conduction paths are the same in firn and ice. To evaluate the variation of resistivity with density, we have considered five dielectric mixture models that fit the available data on the high‐frequency dielectric constant of firn. Only Looyenga's equation fits the field data for dc resistivity. In the upper 900 m of the ice sheet, where impurity concentrations are known from core samples, we find no correlation between resistivities and the concentrations of salts or acids. Instead, we find it likely that resistivities are correlated with the crystal size, hence with the Holocene‐Wisconsin boundary in the ice column. A pronounced increase in resistivity, to a value comparable with that in temperate glacier ice, occurs deep within the ice sheet. We attribute this to a large increase in the size and irregularity of the ice crystals, which destroys the continuity of the impurity shells surrounding the ice crystals that we believe supply the conduction paths (Shabtaie and Bentley, 1994a). High resistivity does not imply removal of the impurities from the system; moderate concentrations of impurities can be accommodated by locating them in disconnected domains.