Permafrost geochemistry and retrogressive thaw slump morphology (Peel Plateau, Canada)

In ice-rich hummocky terrains spanning broad swaths of the Canadian Arctic, accelerating permafrost thaw and terrain subsidence (thermokarst) are exposing materials that were previously locked away for millennia. Among the most significant implications of thermokarst is the rapid mobilization of these materials into modern biogeochemical cycles. For instance, retrogressive thaw slumps (RTSs) can release large amounts of ions, carbon, nutrients, and sediments into streams, thereby reshaping freshwater ecosystems and elemental cycles. As features that expose ancient permafrost and rapidly respond to modern environmental change, RTSs offer a relatively accessible window into the past and a potential glimpse into the future of Arctic biogeochemical cycles. Here, we characterize the permafrost geochemistry and feature morphology of eight RTSs on the Peel Plateau (NT, Canada), to understand the effects of intensifying thermokarst on land-water linkages, Arctic biogeochemistry, and freshwater ecosystems. Our measurements were made at RTSs across diverse terrains in the Stony Creek and Vittrekwa River watersheds, to capture potential variability in permafrost geochemistry. In agreement with previous studies on RTS effects on the chemistry of streams on the Peel Plateau, our measurements of the inorganic and organic chemistry of solutes in permafrost and of rill runoff thaw streams within RTSs reveal that potentially large stores of ions, carbon, and nutrients within regional permafrost are susceptible to exposure and mobilization following thaw. Our terrestrial laser-ranging measurements of RTS depth (i.e. headwall height) provide an opportunity to assess past and future morphological change. Together, these observations provide a snapshot of the geochemical and geomorphologic change that may be expected as thermokarst intensifies across the Canadian Arctic.