Deep geoelectric soundings using a Schlumberger array were carried out at Dome C, Antarctica. To penetrate the 3 500 m thick ice, electrode half spacings up to 8 km (the largest yet made on polar ice) were used. A constant-current dc transmitter with voltages up to 10 kV, resulting in constant currents of up to 10 mA, was employed; potentials were measured with an electrometer and recorded continuously on an x-y recorder.

A computer program has been developed to calculate apparent resistivities on an ice sheet in which the density, temperature, and impurities, and thus the actual resistivity, vary continuously with depth. Preliminary models show that the actual resistivity at a depth of about 500 m increases downward by a factor of about three, and that elevated resistivities must persist to much greater depth. This change in resistivity appears to be linked to transition from ice-age to Holocene ice.

The cause of this resistivity increase is not well understood, and may be attributed to any of several physical and chemical changes that also occur at about the same depth.