The Electrical Behaviors of Antarctic Ice Drilled at Mizuho Station, East Antarctica

The electrical properties of Antarctic firn and ice cores drilled at Mizuho Station (70°41\u2753"S, 44°19\u2754"E) to the depth of 145m were studied in a wide range of frequency (0.1Hz to 1MHz) and temperature (0 to -50℃). Remarkable differences were found between the cores taken from depths shallower than 55m and those from deeper parts. Dielectric properties of the cores above 55m, corresponding to cores permeable to air flow and with densities less than 840kg・m^, could be explained as those of heterogeneous mixture-dielectrics of ice and air, though the physical meaning of the activation energies, namely 0.20±0.02eV (19.3±1.5kJ・mol^) for dielectric relaxation and 0.21±0.02eV (20.3±1.5kJ・mol^) for high-frequency conduction, were not clarified completely. Cores deeper than 55m, corresponding to impermeable cores with densities higher than 840kg・m^, showed extremely large dielectric constants and conductivities with activation energies of 0.19±0.02eV (18.4±1.5kJ・mol^) and 0.23±0.02eV (22.2±1.5kJ・mol^) for dielectric relaxation and high-frequency conduction, respectively. The difference of the electrical properties from those of ordinary pure ice suggests that some unknown mechanism is working in the deep polar ice probably because of the abnormal circumstances due to high hydrostatic pressure and high homologous temperature, coupled with the sophisticated stress field. Based on the results of the present electrical measurements, the alteration of densification mechanisms was suggested to occur at a depth around 30m corresponding to the density of 730kg・m^, where the bonding and compaction of composing ice particles were regarded to have reached their optimum mode, which was also confirmed by petrographic analyses of cores such as areas of internal free surfaces and grain boundaries