Thaw Lake Expansion in a Coupled Model of Heat Transfer and Mass Movement

Expansion of thaw lakes contributes greenhouse gases to the atmosphere by the decomposition of thawed organic sediments beneath and around lake basins. However, the degree to which air temperature, precipitation, and ground ice content affect rates of thaw lake expansion remains unconstrained. To investigate controls over thaw lake expansion, we use a two-dimensional numerical model which simulates coupled expansion of thaw lake margin and talik development over several thousand years. A finite difference model for conductive heat transfer, incorporating latent heat around the thaw front, is coupled with a cellular model for mass movement and thaw-driven subsidence. In the mass transport model, the stability of a cell on the lake margin is determined by the gradient of the cell. The probability of erosion increases non-linearly for slopes approaching the critical angle of the ground material. The distance a cell is redeposited into the lake basin is a function of the bathymetry of the entire basin (i.e. the position of all other lake bottom cells relative to the position of the eroding cell). Modeled lakes reproduce characteristics of natural thaw lakes in the Yukon Coastal Plain, including thaw bulb size from prior publications, and bathymetry measured with differential GPS. Preliminary sensitivity results indicate rates of retreat may be primarily controlled by ground ice content, but high air and water temperatures and longer thaw seasons promote deeper talik development and more rapid subsidence-based expansion. Lake morphology may also be controlled by the ground ice content of the permafrost. Notably, modeled lakes with high excess volumetric ground ice (> %50) and low rates of erosion develop littoral shelves and deep central pools, such as those found on the Tuktoyaktuk Peninsula, NWT. Modeled lakes with high excess ice and high rates of erosion develop bowl shaped basins, such as those found on the Seward Peninsula, Alaska.