Retreat of thaw lake margins in a two-dimensional coupled model of heat transfer and mass wasting

Thaw lakes --widespread thermokarst features in lowland, ice-rich permafrost of Alaska, Canada and Siberia-- expand by interactions between thawing and collapse of ice-rich permafrost, and redistribution of sediment within the basin, modulated by air and water temperatures. To investigate dependance of thaw lake expansion on climate change over 10- 103y, we introduce a two-dimensional, cross sectional numerical model of thaw lake expansion which combines heat conduction and thaw-subsidence with diffusive and advective mass wasting. Under conditions for the Seward Peninsula, AK, subaerial and subaqueous margins of modeled lakes are inclined 20° and 3° respectively, with 0.26±0.01 m/yr bank retreat after 500 years (range is 1-sigma for 10 model realizations), compared to a natural lake from this region with margins inclined ~23° and 3° and 0.4 m/yr bank retreat (measured using differential GPS and sonar). Lakes modeled under conditions in the northern Yukon, have maximum depth 2.1 m, taliks thickness 8.7 m, margins inclined 8°, and 0.05 m/yr bank retreat after 500 years, similar to natural lakes in this region with depths 1.6--4 m, and subaqueous margins inclined <10°. Under a warmer-than- present climate (modern MAAT+3°C), rates of expansion increase to 0.44 m/yr in the Seward model and to 0.07 m/yr in the Yukon model, consistent with observations of increased thermokarst activity in northern Canada and Alaska during Holocene and Pleistocene warm periods, and thermokarst nearly halts in full glacial climates. The model reproduces morphology and dynamics similar to natural thaw lakes, indicating usefulness in investigating thaw lake sensitivity to anthropogenic climate warming. Supported by the Natural Science and Engineering Research Council