The ground thermal regime of the Peel Plateau, Northwest Territories, Canada

Abstract

The ground thermal regime of continuous permafrost was investigated on Peel Plateau, Northwest Territories, Canada. Extensive road maintenance has been necessary on the Plateau due to the thaw of ground ice near the Dempster Highway road embankment. This thesis examines permafrost conditions in undisturbed terrain and in disturbed ground at the road embankment. Field data from 2010-15 provided a systematic examination of permafrost temperatures in forest and tundra vegetation on Peel Plateau and of the thermal disturbance from snow accumulation at the highway. Ground temperatures and measurements of associated controlling factors were used to characterize permafrost conditions across an elevational treeline in undisturbed settings. Permafrost conditions were also examined at the embankment toe and at a snow fence near the road to characterize disturbed ground thermal regimes in the region. Numerical simulations were calibrated with field measurements to assess the influence of varying snow accumulation characteristics (depth, density, rate, timing) on the evolution of ground temperatures at disturbed sites. Annual mean permafrost temperatures increased across treeline from about -2.5 ◦C in lowland forest to about -1.5 ◦C in tundra, coinciding with higher air temperatures due to winter inversions, and earlier snow accumulation at tundra sites. Rapid and deep snow accumulation at the road embankment toe has resulted in annual mean ground temperatures typically just below 0 ◦C, thaw depths in excess of 5 m, and the development of perennially unfrozen zones (taliks). Numerical simulations of the ground thermal regime closely reproduced measured temperatures near the road. This enabled the effect of limiting snow depth and increasing density to be investigated as a potential method to mitigate permafrost thaw. The simulations indicated that ground temperatures and thaw depths may thereby be significantly reduced at the embankment toe. The long-term disturbance to permafrost was then investigated in the field and simulated numerically in two dimensions at a snow fence near the road embankment. A talik developed under the fence after 25 years in the simulation. Permafrost thaw in the simulation continued for several decades without reaching equilibrium, demonstrating the sensitivity of warm permafrost to changes in surface conditions that initiate thermokarst.