Spatial Variations in Seasonal Thaw Rates on a Subarctic Peat Plateau

Abstract:

Much of Canada’s subarctic is experiencing significant land-cover transformation as a result of a warming climate. Permafrost thaw-induced land-cover changes in the sporadic discontinuous permafrost zone (SDPZ) have altered the hydrologic response of basins in this region through increasing hydrological connectivity of the landscape. It has been well-documented that the observed changes in land-cover and permafrost thaw rates are connected; however, it is unclear why these landscape-wide changes occur at different rates. To better understand these changes, an isolated permafrost-cored peat plateau was selected and intensively studied at the Scotty Creek Research Station in Northwest Territories, Canada. This plateau, surveyed using geophysical methods in 2010 and again in 2019, is bounded by four permafrost-free terrain features, including a linear disturbance, channel fen, lake, and bog. This research aims to: (1) quantify the present volume of the permafrost body; (2) investigate how the permafrost body has changed from 2010 to 2019; and (3) compare the relative influence of adjacent permafrost free wetland and collapse-scar features on the differential thaw rates observed. To estimate changes in the areal extent of the permafrost body, historical air photographs, high-resolution satellite imagery (WorldView2) and LiDAR-derived products were used. Similarly, changes in the thickness of the permafrost body were estimated through comparison of 2010 and 2019 geophysical surveys and near-surface measurements.Results from remotely sensed imagery and geophysical surveys indicate that the spatial extent of the permafrost body has receded both laterally and vertically, with the majority of degradation located adjacent to a fen. Collocated geophysical surveys from 2010 and 2019 suggest that previously where values of 5000 Ωm extended to depths of approximately 10 m, presently extend to depths of approximately 9 m. Preliminary estimates of volumetric change of the permafrost body from 163 x 10³ m³ to 139 x 10³ m³, representing a decrease of ~ 14% since the 2010 baseline. This study improves the understanding of the patterns of permafrost thaw and provides insight into the boundary conditions between permafrost and non-permafrost terrain in the SDPZ.