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‘Warm’ Tundra: Atmospheric and Near‐Surface Ground Temperature Inversions Across an Alpine Treeline in Continuous Permafrost, Western Arctic, Canada

Permafrost conditions were examined between 2010 and 2014 at four sites across an alpine treeline on Peel Plateau, Northwest Territories, Canada. Ground and air temperature sensors were installed in forest and tundra between 30 and 500 m asl. Annual mean air temperatures increased and the number of freezing degree days declined with elevation, due to persistent winter air temperature inversions. The annual mean temperature at the permafrost surface (Tps) in mineral soils increased with elevation from about −2.5 °C in lowland forest to about −1.5 °C in dwarf shrub tundra. The increase in Tps coincided with higher air temperatures and earlier snow accumulation at tundra sites. The higher Tps in alpine tundra compared to lowland forest in Peel Plain contrasts with the northward decrease in Tps across latitudinal treeline elsewhere in the western Arctic. An increase in Tps with elevation may be common in Arctic mountain environments due to the prevalence of atmospheric temperature inversions in winter. In such contexts, although vegetation characteristics are governed by summer climate, permafrost conditions are critically influenced by the winter regime. The tundra permafrost on Peel Plateau is considerably warmer and, hence, more sensitive to disturbance than perennially frozen ground north of treeline in other parts of the western Arctic. Copyright © 2015 John Wiley & Sons, Ltd.