In-situ measurement of the low frequency permittivity of sea ice

Cross-borehole resistivity tomography, previously used to measure the anisotropic resistivity structure of first-year sea ice, has been adapted to measure the low frequency electric permittivity over the frequency range 10 Hz - 100 kHz. Results from measurements made using a purpose built instrument in both McMurdo Sound, Antarctica and Barrow, Alaska are reported. These show dielectric relaxation to occur at a frequency of around 10 KHz, with prominent low frequency effects due to space charge polarization. Modelling of the results in terms of Debye and Cole-Cole models allows some insights into the variation of key parameters with factors such as brine volume fraction and temperature. Results from McMurdo Sound, where there is a depth transition from columnar ice to incorporated platelet ice, also suggest the existence of structural effects.