Spatially Resolved Projections of Permafrost Thaw, Microtopography Change, and Landscape Hydrology for a Polygonal Tundra Site
Scott L. Painter1* (email@example.com), Ethan T. Coon1, Ahmad Jan Khattak1,2, Julie D. Jastrow3, Colleen Iversen1
1Climate Change Science Institute, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN; 2Office of Water Prediction, National Water Center, National Oceanic and Atmospheric Administration, Tuscaloosa, AL; 3Environmental Science Division, Argonne National Laboratory, Lemont, IL
Microtopography change caused by melting ground ice has been identified as a mechanism that could accelerate permafrost thaw in polygonal tundra. Researchers used the integrated surface and subsurface cryohydrology advanced terrestrial simulator (ATS) to investigate the effect of that positive feedback mechanism. ATS solves coupled equations for surface and subsurface thermal hydrology and includes representations of subsidence caused by melting excess ice and resulting effects on microtopography. The simulations of a polygonal tundra site near Utqiaġvik, AK were informed by spatially averaged depth profiles of permafrost ice content, an important control on the rate of subsidence, which were estimated from intensive sampling of transects across six ice-wedge polygons (from trough center to trough center). The simulations build on previous small-scale ATS simulations that agree well with multiyear observations of snow depth, suprapermafrost water table depth, and depth-resolved soil temperature. The new simulations of a small catchment comprising 468 ice wedge polygons agree well with published estimates of landscape runoff, evapotranspiration, and subsidence. Projections indicate 63 cm of bulk subsidence from 2006 to 2100 in the RCP8.5 climate. Permafrost thaw, as measured by the increase in active layer thickness, is not accelerated significantly by subsidence. Projected active layer thickness at year 2100 is approximately 180 cm when subsidence is included compared to about 160 cm when it is neglected. However, if thaw is measured by the amount of previously frozen carbon that thaws each summer, subsidence has a greater impact; the amount of soil solids thawing each summer is roughly 65% higher in the subsiding case compared to the nonsubsiding case. In these simulations, previously identified positive feedbacks between subsidence and thaw are self-limiting on decadal time frames because microtopographic changed caused by melting ground ice, specifically, the transitions from low-centered to high-centered polygons, decreases depression storage and increases landscape runoff, resulting in drier tundra with weaker surface and atmosphere coupling. Those changes in hydrology help maintain stream flows in a warming climate but also lead to drier tundra conditions.
Painter, S.L., et al. 2023. “Drying of Tundra Landscapes will Limit Subsidence-Induced Acceleration of Permafrost Thaw,” Proceedings of the National Academy of Sciences 120, e2212171120.