Thaw Bulb Dimension Imaging Using Continuous Resistivity Soundings, Seward Peninsula, Alaska

Thaw bulb dimensions are measured using continuous resistivity soundings on Seward Peninsula thermokarst lakes. This information increases our understanding of thermokarst processes and volume of thawed, carbon rich sediment available to release biogenic greenhouse gasses. This novel measurement technique uses a small motorized boat as a platform to measure location, lake depth, and continuous resistivity soundings. Resistivity data is collected using a floating, towed cable of thirteen graphite electrodes to inject a current and measure the resultant electrical potential field, which is sensitive to the thickness of the thawed, conductive sediment. A resistivity distribution model of the earth is developed using a one dimensional laterally constrained inversion of the potential measurements, with a simple conceptual model of interval thicknesses and resistivity of the water layer, talik, and the underlying permafrost as a half space. This inversion scheme takes advantage of the a priori information available such as water thickness and resistivity as well as the resistivity of the talik sediment and underlying permafrost. Model fit is evaluated using a model residual error as well as a parameter covariance analysis that allows for determination of model interpretation confidence. The resulting geometry image of the talik clearly shows the talik shape and changes in talik shape indicate previous generations of thermokarst development not apparent from analysis of surface geomorphology. This data set improves our understanding of thermokarst processes and allows for volume estimations of the thawed sediments.