Slope thermokarst transforms permafrost preserved glacial landscapes and effects propagate through Arctic drainage networks.

Recent intensification of slope thermokarst is transforming permafrost preserved glaciated landscapes and causing significant downstream effects. In this paper we: A) Describe the thaw-related mechanisms driving the evolution of slope to stream connectivity; B) define the watershed patterns of thermokarst intensification; and C) project the cascade of effects through the Arctic drainage networks of northwestern Canada. The power-law relationships between disturbance area and volume, and thickness of permafrost thawed, in conjunction with a time-series of disturbance mapping show that the non-linear intensification of slope thermokarst is mobilizing vast stores of previously frozen glacial sediments linking slopes to downstream systems. Mapping across a range of catchment scales indicates that slope thermokarst predominantly affects first and second order streams. Slope sediment delivery now frequently exceeds fluvial transport capacity of these streams by several orders of magnitude indicating long-term perturbation. Mapping shows slope thermokarst is directly affecting over 6760 km of stream segments, over 890 km of coastline and over 1370 lakes across the 1,000,000 km² Arctic drainage basin from continuous permafrost of northwestern Canada. The downstream projection of thermokarst disturbance increases affected lakes by a factor of 4 and stream length by a factor of 7, and suggests that fluvial transfer has the potential to yield numerous thermokarst impact zones across coastal areas of western Arctic Canada. The Prince of Wales Strait between Banks and Victoria Islands is identified as a hotspot of downstream thermokarst effects, and the Peel and Mackenzie rivers stand out as principle conveyors of slope thermokarst effects to North America’s largest Delta and to the Beaufort Sea. The distribution of slope thermokarst and the fluvial pattern of sediment mobilization signal the climate-driven rejuvenation of post-glacial landscape change and the triggering of a time-transient cascade of downstream effects. Geological legacy and the patterns of continental drainage dictate that terrestrial, freshwater and marine environments of western Arctic Canada will be a hotspot of climate-driven change through the coming centuries.