Recent Increases in Permafrost Thaw Rates and Areal Loss of Palsas in the Western Northwest Territories, Canada

Abstract

Decay of palsas can indicate permafrost status, particularly in regions where air temperatures have increased rapidly in recent decades. Using weather data, annual surveys of active‐layer thickness, and analyses of high‐resolution aerial imagery from the eastern Selwyn/western Mackenzie Mountains, NT, Canada, we show that permafrost temperatures have increased, active layers have deepened, and palsa areal extents have decreased considerably since the 1940s. High‐altitude palsas thawed quickly from the 1940s to the 1980s, although some low‐altitude palsas have recently decreased rapidly in areal extent due to peat‐block calving. The linear rate of increasing active‐layer thickness may not be congruent with the non‐linear rate of areal loss of palsas. The rapid and episodic collapse of palsas at some sites highlights the necessity to consider hydrology, vegetation cover, landscape position, and morphology in palsa dynamics in addition to a warming climate. Copyright © 2017 John Wiley & Sons, Ltd.

Wildfire as a major driver of recent permafrost thaw in boreal peatlands

“…The second assumption was that young thermokarst bogs persist in the landscape 100 ± 50 years (95% confidence interval) before developing into mature thermokarst bogs (Supplementary Table 5 ), signifying that no young thermokarst bog currently present developed >150 years ago. The third assumption was that the rate of thermokarst bog expansion is likely to have increased over the last 30 years also in unburned peatland parts, due to ongoing climate change 20 – 22 (see Methods for further details). Using these three assumptions, we estimated the rate of young thermokarst bog development prior to the fire, following fire in burned parts, and following fire in unburned parts for each of our four sites (Supplementary Fig.…”

“…This assumption is based on 14 C and Pb dating of peat cores (Supplementary Table 5 ), and implies that all young thermokarst bogs currently present in peatland developed <150 years ago. Thirdly, we assumed that that the rate of thermokarst bog development likely have increased also in unburned peatland parts over the last 30 years, due to ongoing climate change 20 – 22 . For this third assumption we defined a 95% CI for the relative rate of thermokarst bog development in unburned peatland parts before and after the year of fire.…”

Reviews and syntheses: Changing ecosystem influences on soil thermal regimes in northern high-latitude permafrost regions

“…In tundra, shrub canopies trap blowing snow, leading to localized deepening of snow cover and higher winter soil temperatures (Domine et al, 2015;Liston et al, 2002;Marsh et al, 2010;Myers-Smith and Hik, 2013;Sturm et al, 2001Sturm et al, , 2005. However, shrub canopies can bend in winter under the snowpack potentially leading to different amounts of snow trapping in years with heavy wet snow vs. dry snow in early winter (Marsh et al, 2010;Ménard et al, 2014). Even buried vegetation can lead to turbulent airflow that transports snow in complex patterns (Filhol and Sturm, 2015), which creates spatially variable ground temperatures in a given year.…”

“…While the accompanying increases in R N will lead to sensible heating of the atmosphere at regional to local scales (Chapin III et al, 2005), they do not have a direct first order effect on T SG or K T . In the spring thaw period when snow covers the landscape and solar radiation is high, this increase in R N is largest (Liston et al, 2002;Marsh et al, 2010;Pomeroy et al, 2006) and may accelerate snow melt (Loranty et al, 2011;Sturm et al, 2005). This could lead to a longer snow-free season and greater G during the summer thaw period; however, this snow-reducing effect can be offset by the snow-trapping effects of vegetation (Sturm et al, 2005).…”

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

“…It is thus a warm type of permafrost and its distribution is highly sensitive to climate changes (Aalto et al, , 2017; Fronzek et al, ; Luoto et al, ). Climate change has already driven the limit of continuous and discontinuous permafrost in the North Hemisphere northward (Thibault & Payette, ), and ongoing degradation of peat plateaus, which started at least in the 1950s, is observed in the Canadian Arctic and Fennoscandia (Borge et al, ; Jones et al, ; Mamet et al, ; Payette et al, ). Analyzing aerial imagery, Borge et al () quantified the evolution of the areal extent of four peat plateau sites in Northern Norway (Finnmark) between the 1950s and the 2010s and reported a decrease of their lateral extent between 33 and 71%, with the largest lateral changes during the last decade.…”