Microtopographic control on the ground thermal regime in ice wedge polygons

Abstract

Abstract. The goal of this research is to constrain the influence of ice wedge polygon microtopography on near-surface ground temperatures. Ice wedge polygon microtopography is prone to rapid deformation in a changing climate, and cracking in the ice wedge depends on thermal conditions at the top of the permafrost; therefore, feedbacks between microtopography and ground temperature can shed light on the potential for future ice wedge cracking in the Arctic. We first report on a year of sub-daily ground temperature observations at 5 depths and 9 locations throughout a cluster of lowcentered polygons near Prudhoe Bay, Alaska, and demonstrate that the rims become the coldest zone of the polygon during winter, due to thinner snowpack. We then calibrate a polygon-scale numerical model of coupled thermal and hydrologic processes against this dataset, achieving an RMSE of less than 1.1 • C between observed and simulated ground temperature. Finally, we conduct a sensitivity analysis of the model by systematically manipulating the height of the rims and the depth of the troughs and tracking the effects on ice wedge temperature. The results indicate that winter temperatures in the ice wedge are sensitive to both rim height and trough depth, but more sensitive to rim height. Rims act as preferential outlets of subsurface heat; increasing rim size decreases winter temperatures in the ice wedge. Deeper troughs lead to increased snow entrapment, promoting insulation of the ice wedge. The potential for ice wedge cracking is therefore reduced if rims are destroyed or if troughs subside, due to warmer conditions in the ice wedge. These findings can help explain the origins of secondary ice wedges in modern and ancient polygons. The findings also imply that the potential for re-establishing rims in modern thermokarst-affected terrain will be limited by reduced cracking activity in the ice wedges, even if regional air temperatures stabilize.

Feedbacks Between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons, Arctic Coastal Plain, Alaska

“…This lateral flux increased in magnitude with rim height, since taller rims accumulated less snowpack, and therefore became colder in winter. The capacity of rims to enhance subsurface cooling in winter through this mechanism has been well documented in previous studies (e.g., Abolt et al, 2018;Cable, 2016;Christiansen, 2005;Morse & Burn, 2014), but these investigations have either not focused on, or not detected, a meaningful relationship between the presence of rims and thaw intensity in the summer. Our analysis suggests that preferential cooling through the rims meaningfully impacts subsequent thaw only under special conditions not explored in previous work-that is, beneath wide and deep thermokarst pools, where a talik has initiated (Figure 3b, trough depths of 65-85 cm).…”

Mechanistic Modeling of Microtopographic Impacts on CO2 and CH4 Fluxes in an Alaskan Tundra Ecosystem Using the CLM‐Microbe Model

“…Polygonal ground patterns create a complex mosaic of microtopographic features with poorly drained low‐centered polygons (LCPs) surrounded by high rims and well‐drained high‐centered polygons (HCPs) surrounded by low trough as results of the annual freeze–thaw cycles across the northern Alaskan coastal plain (Hinkel et al, ; Throckmorton et al, ; Zona et al, ). Microtopography strongly affects soil water content and active layer depth (Atchley et al, ; Grant, Mekonnen, Riley, Arora, & Torn, ; Grant, Mekonnen, Riley, Wainwright, et al, ; Lu & Zhuang, ), soil temperature and thermal conductivity (Abolt et al, ; Kumar et al, ), soil pH and O 2 availability (Lipson et al, ; Zona et al, ), soil chemistry (Lipson et al, ; Newman et al, ; Semenchuk et al, ), vegetation types and canopy height (Davidson et al, ; von Fischer et al, ), and microbial community structure (Tas et al, ; Wagner et al, ). Therefore, the large spatial heterogeneities in microtopographic features are critically important for modeling and predicting the ecosystem carbon (C) exchange in Arctic tundra ecosystems.…”

Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions

“…Cresto Aleina et al (2013) presented a data-driven, scalable approach to assessing the hydrological connectivity of polygonal tundra and reported a non-linear hydrological control on methane fluxes. Several studies have noted the influence of micro-topography and lateral fluxes on subsurface thermal and hydrological regimes, as well as on the biogeochemical processes in polygonal tundra areas (Kumar et al, 2016;Grant et al, 2017a, b;Bisht et al, 2018;Abolt et al, 2018). Liljedahl et al (2016) investigated the hydrological implications of a transition from low-centred polygons to high-centred polygons and noted the important influence of spatially heterogeneous snow distribution.…”