Rapid initialization of retrogressive thaw slumps in the Canadian high Arctic and their response to climate and terrain factors

Abstract

An increase in retrogressive thaw slump (RTS) activity has been observed in the Arctic in recent decades. However, a gap exists between observations in high Arctic polar desert regions where mean annual ground temperatures are as cold as −16.5°C and vegetation coverage is sparse. In this study, we present a ∼30 year record of annual RTS observations (frequency and distribution) from 1989 to 2018 within the Eureka Sound Lowlands, Ellesmere and Axel Heiberg Islands. Record summer warmth in 2011 and 2012 promoted rapid RTS initialization, increasing active slumps from 100 in a given year or less to over 200 regionally and promoting RTS initiation in previously unaffected terrain. Differential GPS and remote sensing observations of 12 RTSs initiated during this period (2011-2018) provided a mean headwall retreat rate for all RTSs of 6.2 m yr −1 and for specific RTSs up to 26.7 m yr −1 . To better understand the dynamics of climate and terrain factors controlling RTS headwall retreat rates we explored RTS interactions by correlating headwall retreat with climate factors (thawing degree days, annual rainfall and annual snowfall) and terrain factors (aspect and slope). Our findings indicate a sensitivity of cold permafrost in the high Arctic to climate-driven thermokarst initiation, but the decoupling of RTS dynamics from climate appears to occur over time for individual RTS as terrain factors take on a greater role controlling headwall retreat. Detailed observations of thermokarst development in a high Arctic polar desert permafrost setting are important as it demonstrates the sensitivity of this system to changes in summer temperatures and highlight differences to changes occurring in other Arctic permafrost regions.

Climate Change Drives Widespread and Rapid Thermokarst Development in Very Cold Permafrost in the Canadian High Arctic

“…The rapid transfer of heat from air to soil in High Arctic environments has been observed previously where short‐lived but intense warm events are thought to have forced widespread active layer deepening during a single warm summer of deeper thaw (Fraser et al, ; Lamoureux & Lafrenière, ; Lewis et al, ; Lewkowicz, ). Recent observations from the Canadian High Arctic link higher than normal summer warmth to a rapid increase in thaw‐related processes including active layer detachment slides, retrogressive thaw slumps, and ice‐wedge melt (Fraser et al, ; Lewkowicz & Way, ; Ward Jones et al, ). Across all of our sites TI values were 2 to 3 times higher than historical norms (1979–2000) throughout our observation period (2003–2016; Figure a and Table S3), and as established through basic analytical solutions for heat transfer such as the Stefan equation (equation ), there was a strong relationship between TI and active layer thickness (Nelson et al, ; Romanovsky & Osterkamp, ; Figure a).…”

“…The majority of top‐down permafrost degradation studies focus on the geomorphic response of ice‐rich permafrost to warming through the application of field surveys (Kanevskiy et al, ; Kokelj et al, ; Lewkowicz, ; Ward Jones et al, ), remote sensing (Frost et al, ; Kokelj et al, ; Lewkowicz & Way, ; Raynolds et al, ), and susceptibility mapping (Rudy et al, ). In such studies, regional climate records are frequently utilized in lieu of direct, local, ground, and air temperature measurements, to infer the cause of permafrost degradation.…”

“…To date, the vulnerability of High Arctic landscapes to climate change‐driven permafrost degradation has been illustrated primarily through its impact on hydrology (Lamoureux & Lafrenière, ; Lewis et al, ), hillslope processes (Lewkowicz, ; Lewkowicz & Way, ; Segal et al, ), and downstream impacts on sedimentology and geochemistry (Rudy et al, ). Such permafrost‐related disturbance events have been attributed to a higher than normal summer air temperature (Biskaborn et al, ; Kokelj et al, ; Lewkowicz, ; Ward Jones et al, ). Despite these observations, the documented changes are not directly linked to, or directly supported by, in time series data to link warm summer air temperatures, corresponding changes in active layer thickness, and terrain response.…”

Impacts of Degrading Ice‐Wedges on Ground Temperatures in a High Arctic Polar Desert System

“…However, since that study, Eureka has experienced its five warmest Julys on record occurring in 2011, 2015, 2012, 2016, and 2009 (Figure ). The 2011 and 2012 summers were particularly impactful with a threefold increase in thermokarst affected areas observed within the whole of the Eureka Sound Lowlands (encompassing the Fosheim Peninsula), including widespread initialization of retrogressive thaw slumps and the complete melting out of IWs in some areas of the Fosheim Peninsula (Pollard et al, ; Ward Jones et al, ). An increase in IW trough depth would have also occurred.…”

“…IW polygon systems can transition to a thermokarst phase by developing high‐centered polygons as troughs subside and become more connected (Liljedahl et al, ; Mackay, ). Thermokarst occurs as a result of a deepening of the active layer, which is caused either by increased summer temperatures (Couture & Pollard, ; Fraser et al, ; Pollard et al, ; Shur & Jorgenson, ; Ward Jones et al, ), or by surface disturbances such as fire (Jones et al, ), erosion (Lantuit & Pollard, ; Ramage et al, ), or anthropogenic impact (Becker & Pollard, ; Raynolds et al, ). IW thermokarst drives microtopographic changes and succession dependent on the amount of degradation that has occurred.…”