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 topography on near-surface ground temperatures. Because ice wedge polygon topography is prone to rapid change in a changing climate, and because cracking in 10 the ice wedge depends on thermal conditions at the top of the permafrost, feedbacks between topography and ground temperature can shed light on the potential for future ice wedge cracking in the Arctic. We first report on a year of subdaily ground temperature observations at five depths and nine locations throughout a cluster of low-centered polygons near Prudhoe Bay, AK, 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 15 RMSE of less than 1.2°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 deeper troughs lead to increased snow entrapment, promoting insulation of the ice wedge. Rims act as preferential outlets of subsurface heat; increasing rim size decreases winter temperatures in the ice wedge. The potential for ice wedge cracking is therefore reduced if rims are destroyed or if troughs subside, due to warmer 20 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 reestablishing rims in modern thermokarst-affected terrain will be precluded by reduced cracking activity in the ice wedges, even if regional air temperatures stabilize.

Impacts of Degrading Ice‐Wedges on Ground Temperatures in a High Arctic Polar Desert System

“…This process likely generated IW 1, and we propose this as a mechanism of IW polygon dynamics over time (Haltigin et al, ). Polygon center‐cooling was also demonstrated in low centered polygons using modeling in Abolt et al (). We believe trough density increases over time as older IWs reach advanced stages of degradation.…”

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

“…Our meshes were constructed with a three‐dimensional pie wedge shape, representing an idealized, radially symmetric polygon (Figure ). In each instance, mineral soil extending to a bottom boundary at 50 m depth was overlain by a 30 cm mantle of peat‐rich soil, as observed at a site near Prudhoe Bay, Alaska (Abolt et al, ). This site was proximal to, but outside of, a drained thaw lake basin and was characterized by epigenetic ice wedges (i.e., ice wedges which have developed beneath a stable land surface, rather than one which is aggrading or eroding).…”

“…Each of our simulations was constructed within version 0.86 of Amanzi‐ATS (Coon et al, ) (https://github.com/amanzi/ats), an ecohydrology code designed to simulate the ground hydrologic and thermal regimes of variably saturated soils in one, two, or three dimensions. In previous studies, Amanzi‐ATS has been applied and validated in diverse permafrost settings (Atchley et al, ; Harp et al, ; Jafarov et al, ; Schuh et al, ; Sjöberg et al, ), including polygonal terrain, where microtopography was represented employing either simplified 2‐D meshes, or an array of 1‐D meshes (Abolt et al, ; Atchley et al, ; Jan et al, ). At its core, Amanzi‐ATS uses a flexible multiphysics framework to solve simultaneously for conservation of energy and water mass at the surface, in the subsurface, and in the snowpack (Coon et al, ).…”

“…This site was proximal to, but outside of, a drained thaw lake basin and was characterized by epigenetic ice wedges (i.e., ice wedges which have developed beneath a stable land surface, rather than one which is aggrading or eroding). Soil hydraulic and thermal parameters (Table S1) were identical to those used by Abolt et al (), which were derived from laboratory analysis of cores taken from an LCP at the site. This general parameterization for soil stratigraphy and subsurface physical properties was held constant throughout our sensitivity analysis.…”

“…Meteorological data were extracted or derived from the output of the Noah Land Surface Model, a component of NASA's Global Land Data Assimilation System, which simulates global meteorological conditions at a spatial resolution of 0.25° and a temporal resolution of 3 hr (Rodell et al, ). Output was extracted from the pixel centered at 148.875°W, 69.875°N, the same location used previously to validate the soil parameters summarized in Table S1 in a polygon‐scale numerical model of thermal hydrology (Abolt et al, ). Variables used to force simulations in Amanzi‐ATS included air temperature, relative humidity, wind speed, incoming shortwave radiation, incoming longwave radiation, rainfall rate, and snowfall rate.…”