Convection in the active layer speeds up permafrost thaw in coarse grained soils

TL;DR

This study demonstrates that groundwater convection significantly accelerates permafrost thaw in coarse-grained soils by enhancing heat transfer through thermal plumes, leading to faster and more heterogeneous thawing.

Contribution

It introduces a coupled model of ice-water phase change and Darcy flow to quantify convection's impact on permafrost thawing, revealing faster thaw rates and heterogeneity.

Findings

Convection accelerates thawing compared to diffusion.

Thaw depth increases linearly with soil permeability.

Thermal plumes cause heterogeneity in thaw interface.

Abstract

Permafrost thaw is a major concern raised by the ongoing climate change. An understudied phenomenon possibly affecting the pace of permafrost thaw is the onset of convective motions within the active layer caused by the density anomaly of water. Here, we explore the effects of groundwater convection on permafrost thawing using a model that accounts for ice - water phase transitions, coupled with the dynamics of the temperature field transported by the Darcy's flow across a porous matrix. Numerical simulations of this model show that ice thawing in the presence of convection is much faster than in the diffusive case and deepens at a constant velocity proportional to the soil permeability. A scaling argument is able to predict correctly the asymptotic velocity. Since in the convective regime the heat transport is mediated by the coherent motion of thermal plumes across the thawed layer, we find that the depth of the thawing interface becomes highly heterogeneous.