The Role of Advective Heat Transport in Talik Development Beneath Lakes and Ponds in Discontinuous Permafrost

To date, models of talik (perennially unfrozen ground) development beneath lakes and ponds in permafrost terrain have focused on simulations with continuous, thick (≥400 m), cold (<-6°C) permafrost using numerical solutions with solely conductive heat transfer. These models consistently predict only 10s of meters of talik development in centuries to millennia. In contrast, observations of lake loss in subarctic regions characterized by thin (20 to 60m), warm, discontinuous permafrost (≥-2°C) suggest that a through-going sub-lake talik may develop in a matter of decades. We modeled the development of a sub-lake talik under permafrost conditions similar to that observed in the southern Seward Pennisula region of Alaska using the Arctic Hydrology Model (ARCHY). ARCHY is a numerical solution that couples heat transport and groundwater flow including the effect of water phase changes on soil permeability and latent heat content. A comparison of model simulations, with and without near surface subpermafrost groundwater flow, indicate that stable permafrost thicknesses are 2 to 5 times greater in the absence of groundwater flow. Simulations examining the thermal influence of lakes on underlying permafrost suggest that through-going talik can develop in a matter of decades and that the incorporation of advective heat transport reduces the time to complete loss of ice beneath the lake by half, relative to heat transport by conduction alone. This work presents the first quantitative assessment of the rates of sub-lake permafrost loss in a system with near-surface groundwater flow. The results highlight the importance of coupled thermal and hydrologic processes on discontinuous permafrost dynamics.