Subzero temperature dependence of electrical conductivity for permafrost geophysics

Temperature dependence of the electrical conductivity of natural waters due to viscosity-based reduction in ionic mobility is well-established for unfrozen conditions. For cold regions, a model for the temperature dependence of electrolyte conductivity at subzero temperatures is required for geophysical studies of permafrost terrain, for which salinity and tension forces may result in freezing-point depression. Extension of the linear temperature model for unfrozen conditions has been applied to geophysical studies of permafrost, but has not been experimentally validated. The temperature dependence of electrical conductivity is measured at subzero temperatures, but above the depressed freezing point for NaCl solutions at a range of concentrations from seawater to brine. Measurements show near-linear dependence of electrical conductivity on temperature down to the lowest experimental temperature of -9 degrees C with no distinct change in behavior observed for subzero temperatures. Given the observed temperature dependence, the linear temperature-conductivity compensation equation is extended to -9 degrees C with a temperature compensation coefficient of 0.019 degrees C-1 for a reference temperature of 20 degrees C with subzero prediction errors of 1-6%. This equation can be used to compensate for temperature dependence of electrical conductivity with reasonable accuracy for geophysical experiments in permafrost terrain. Subzero accuracy is improved by adopting a quadratic temperature compensation equation that accounts for an observed increase in nonlinear behavior at lower temperatures distant from the reference.