Numerical Assessments of Excess Ice Impacts on Permafrost and Greenhouse Gases in a Siberian Tundra Site Under a Warming Climate

Abstract

Excess ice that exists in forms such as ice lenses and wedges in permafrost soils is vulnerable to climate warming. Here, we incorporated a simple representation of excess ice in a coupled hydrological and biogeochemical model (CHANGE) to assess how excess ice affects permafrost thaw and associated hydrologic responses, and possible impacts on carbon dioxide and methane (CH4) fluxes. The model was used to simulate a moss-covered tundra site in northeastern Siberia with various vertical initializations of excess ice under a future warming climate scenario. Simulations revealed that the warming climate induced deepening of the active layer thickness (ALT) and higher vegetation productivity and heterotrophic respiration from permafrost soil. Meanwhile, excess ice temporarily constrained ALT deepening and thermally stabilized permafrost because of the highest latent heat effect obtained under these conditions. These effects were large under conditions of high excess ice content distributed in deeper soil layers, especially when covered by moss and thinner snow. Once ALT reached to the layer of excess ice, it was abruptly melted, leading to ground surface subsidence over 15–20 years. The excess ice meltwater caused deeper soil to wet and contributed to talik formation. The anaerobic wet condition was effective to high CH4 emissions. However, as the excess ice meltwater was connected to the subsurface flow, the resultant lower water table limited the CH4 efflux. These results provide insights for interactions between warming climate, permafrost excess ice, and carbon and CH4 fluxes in well-drained conditions.

Impacts of Permafrost Degradation on Carbon Stocks and Emissions under a Warming Climate: A Review

“…Tanski et al (2019) claimed that, when seawater eroded each gram of permafrost, 4.3 ± 1.0 mg CO2 would be released into the atmosphere [14]. Parker et al ( 2021) simulated the abrupt thaw of excess ice and found excess-ice meltwater is effective in high CH4 emission; once ice melt is connected to a subsurface flow, CH4 efflux is limited [90]. With an areal extent of 3.6 × 10 6 km 2 , Circum-Arctic thermokarst landscapes cover about 20% of the northern permafrost region, with a similar POC feedback comparable to the extensive and overall permafrost degradation in a gradual manner [91,92].…”