Abstract
Abstract. The intensification of thaw-driven mass wasting is transforming glacially conditioned permafrost terrain, coupling slopes with aquatic systems, and triggering a cascade of downstream effects. Within the context of recent, rapidly evolving climate controls on the geomorphology of permafrost terrain, we (A) quantify three-dimensional retrogressive thaw slump enlargement and describe the processes and thresholds coupling slopes to downstream systems, (B) investigate catchment-scale patterns of slope thermokarst impacts and the geomorphic implications, and (C) map the propagation of effects through hydrological networks draining permafrost terrain of northwestern Canada. Power-law relationships between retrogressive thaw slump area and volume (R2=0.90), as well as the thickness of permafrost thawed (R2=0.63), combined with the multi-decadal (1986–2018) increase in the areal extent of thaw slump disturbance, show a 2 order of magnitude increase in catchment-scale geomorphic activity and the coupling of slope and hydrological systems. Predominant effects are to first- and second-order streams where sediment delivery, often indicated by formation of recent debris tongue deposits, commonly exceeds the transport capacity of headwater streams by orders of magnitude, signaling centennial- to millennial-scale perturbation of downstream systems. Assessment of hydrological networks indicates that thaw-driven mass wasting directly affects over 5538 km of stream segments, 889 km of coastline, and 1379 lakes in the 994 860 km2 study area. Downstream propagation of slope thermokarst indicates a potential increase in the number of affected lakes by at least a factor of 4 (n>5692) and impacted stream length by a factor of 8 (>44 343 km), and it defines several major impact zones on lakes, deltas, and coastal areas. Prince of Wales Strait is the receiving marine environment for greatly increased sediment and geochemical fluxes from numerous slump-impacted hydrological networks draining Banks Island and Victoria Island. The Peel and Mackenzie rivers are globally significant conveyors of the slope thermokarst cascade, delivering effects to North America's largest Arctic delta and the Beaufort Sea. Climate-driven erosion of ice-rich slopes in permafrost-preserved glaciated terrain has triggered a time-transient cascade of downstream effects that signal the rejuvenation of post-glacial landscape evolution. Glacial legacy, ground-ice conditions, and continental drainage patterns dictate that terrestrial, freshwater, coastal, and marine environments of western Arctic Canada will be an interconnected hotspot of thaw-driven change through the coming millennia.
Highlights
Climate-induced permafrost thaw will drive the geomorphic evolution of circumpolar ice-rich landscapes (Kokelj and Jorgenson, 2013) and terrestrial, freshwater, and coastal ecosystems (Vonk et al, 2019)
The first three subsections focus on slopescale processes with an emphasis on the thresholds that have transformed connectivity between thaw-driven mass wasting and downstream systems (Sect. 3.1 and 3.2), as well as the scaling of thaw slump dimensions associated with areal enlargement (Sect. 3.3)
Nonlinear intensification of thaw-driven mass wasting is transforming permafrost-preserved glacial landscapes and downstream connectivity, triggering a cascade of effects that are propagating through Arctic hydrological networks
Summary
Climate-induced permafrost thaw will drive the geomorphic evolution of circumpolar ice-rich landscapes (Kokelj and Jorgenson, 2013) and terrestrial, freshwater, and coastal ecosystems (Vonk et al, 2019). Thawing of ice-rich, glacially conditioned permafrost terrain (Kokelj et al, 2017a) is rapidly mobilizing vast stores of previously frozen materials, reconfiguring slopes, and impacting downstream environments (Fig. 1) (Balser et al, 2014; Rudy et al, 2017a; Tank et al, 2020). These and other similar results highlight the need to quantify slope thermokarst intensification in a robust geomorphic framework, better understand the rapidly evolving linkages between thawing slopes and downstream environments, and predict the propagation of effects across watershed scales. Despite the growing geomorphic and geochemical influence of thaw-driven mass wasting on terrestrial, aquatic, and marine systems (Vonk et al, 2019) and the potential for rapid carbon release (Turetsky et al, 2020), fundamental knowledge gaps persist in our understanding of climatedriven amplification of slope thermokarst, the evolution of downstream linkages, and the cascade of consequences
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