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

Abstract

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 (T ps ) in mineral soils increased with elevation from about À2.5°C in lowland forest to about À1.5°C in dwarf shrub tundra. The increase in T ps coincided with higher air temperatures and earlier snow accumulation at tundra sites. The higher T ps in alpine tundra compared to lowland forest in Peel Plain contrasts with the northward decrease in T ps across latitudinal treeline elsewhere in the western Arctic. An increase in T ps 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.

Quantifying Surface Temperature Inversions and Their Impact on the Ground Thermal Regime at a High Arctic Site

“…Although the levels of absolute relief are less in the High Arctic compared to areas of complex topography in western Canada, the inversion strength when compared directly is substantially greater. During the winter months the surface lapse rate around Dawson City in the continental Yukon has been shown to be greater than +5 °C km -1 for an annual surface lapse rate of about +1 °C km -1 (Lewkowicz and Bonnaventure, 2011), which is similar to that found by Taylor et al (1998) at Norman Wells, Northwest Territories (NWT), and O'Neill et al (2015) across an alpine treeline on Peel Plateau, NWT. At the Alert site this value appears to be about an order of magnitude greater, averaging +50 °C km -1 (+5 °C/100 m) between BH4 and BH5 and +24 °C km -1 (+2.4 °C/100 m) between BH4 and BH3 (Table 3), which agrees with earlier observations in the High Arctic by Bradley et al (1992).…”

“…Recent examples in the literature include the work done by Pagès and Miró (2009) in the Pyrenees, as well as work in western Canada by Taylor et al (1998), Lewkowicz and Bonnaventure (2011), Chaput and Gajewski (2014), and O'Neill et al (2015. The conclusions thus far indicate that inversions are more persistent in winter under stable air conditions.…”

“…Studies in northwestern Canada have shown that ground surface temperatures and even the distribution of permafrost are controlled by the inversion pattern over variable topography (Taylor et al, 1998;Bonnaventure and Lewkowicz, 2013;O'Neill et al, 2015). As a result, this allows permafrost to be present in the valley bottoms where stable cold air can collect, whereas permafrost is then absent at higher elevations above the typical depth of the inversion (Taylor et al, 1998;Bonnaventure et al, 2012).…”

Increased precipitation drives mega slump development and destabilization of ice-rich permafrost terrain, northwestern Canada

“…There is growing field evidence to suggest that slump activity has recently intensified across a range of Arctic landscapes (Lantuit andPollard, 2008 andLantz andKokelj, 2008), but the linkages between climatic drivers and development of larger slumps remains poorly understood (Kokelj and Jorgenson, 2013). Our primary objectives are to determine if thaw slumping has increased in the Peel Plateau region, and to investigate the processes and feedbacks that intensify slump activity.…”

Change in frozen soils and its effect on regional hydrology, upper Heihe basin, northeastern Qinghai–Tibetan Plateau

“…Sub-grid topography may also affect the frozen soil simulation. For example, active layer thickness is different between the low-elevation valleys and higher-elevation slopes due to the temperature inversion caused by the accumulation of cold air in valleys (Bonnaventure et al, 2012;O'Neill et al, 2015). In areas with high groundwater flow rates, laterally advected heat flux may increase the thawing of permafrost Sjöberg et al, 2016).…”