Hydrological transformations induced by climate warming are causing Arctic annual fluvial energy to shift from skewed (snowmelt-dominated) to multimodal (snowmelt- and rainfall-dominated) distributions. We integrated decade-long hydrometeorological and biogeochemical data from the High Arctic to show that shifts in the timing and magnitude of annual discharge patterns and stream power budgets are causing Arctic material transfer regimes to undergo fundamental changes. Increased late summer rainfall enhanced terrestrial-aquatic connectivity for dissolved and particulate material fluxes. Permafrost disturbances (<3% of the watersheds’ areal extent) reduced watershed-scale dissolved organic carbon export, offsetting concurrent increased export in undisturbed watersheds. To overcome the watersheds’ buffering capacity for transferring particulate material (30 ± 9 Watt), rainfall events had to increase by an order of magnitude, indicating the landscape is primed for accelerated geomorphological change when future rainfall magnitudes and consequent pluvial responses exceed the current buffering capacity of the terrestrial-aquatic continuum.

Records of fluvial suspended sediment fluxes are sensitive indicators of hydrometeorological and permafrost change. Here we document the watershed-scale suspended sediment flux response to a period of hydrometeorological change and landscape disturbance in two High Arctic rivers.Net in-channel and extra-channel sediment storage and changing hydrometeorological conditions dampen the downstream transport of increased sediment delivery from localized permafrost slope disturbances. Our results show that the impact of permafrost disturbance is likely a smaller effect than a shift toward a pluvially (rainfall) dominated hydrological regime in these environments. Suspended sediment transport is energy limited under contemporary hydrometeorological conditions, and the transition from a nival to pluvial dominated flow and sediment transfer regime will likely accelerate landscape change in the High Arctic.

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Climate warming and changing precipitation patterns have thermally (active layer deepening) and physically (permafrost-thaw related mass movements) disturbed permafrost-underlain watersheds across much of the Arctic, increasing the transfer of dissolved and particulate material from terrestrial to aquatic ecosystems. We examined the multiyear (2006-2017) impact of thermal and physical permafrost disturbances on all of the major components of fluvial flux. Thermal disturbances increased the flux of dissolved organic carbon (DOC), but localized physical disturbances decreased multiyear DOC flux. Physical disturbances increased major ion and suspended sediment flux, which remained elevated a decade after disturbance, and changed carbon export from a DOC to a particulate organic carbon (POC) dominated system. As the magnitude and frequency of physical permafrost disturbance intensifies in response to Arctic climate change, disturbances will become an increasingly important mechanism to deliver POC from terrestrial to aquatic ecosystems. Although nival runoff remained the primary hydrological driver, the importance of pluvial runoff as driver of fluvial flux increased following both thermal and physical permafrost disturbance. We conclude the transition from a nival-dominated fluvial regime to a regime where rainfall runoff is proportionately more important will be a likely tipping point to accelerated High Arctic change. Fluvial fluxes of dissolved and particulate material from Arctic watersheds are strongly controlled by the presence of permafrost. Arctic fluvial systems have adapted to strong seasonality in flow generation and relatively low inputs of permafrost-derived terrestrial material (e.g., sediment, carbon), with downstream aquatic ecosystems also adapted to this type of low energy regime 1-2. However, Arctic fluvial systems are changing due to permafrost disturbance caused by climate warming and shifting precipitation patterns 3-6. Coupled climate-terrestrial models consistently predict widespread permafrost thaw and disturbance over the next century 7. Multiple pan-Arctic studies show that observed climate change is already transferring significant quantities of terrestrial material to downstream aquatic ecosystems 8-10 as a physical response to increases in the magnitude, frequency, and type of permafrost disturbance 11-14. Several types of widely observed permafrost disturbance can be broadly grouped into two main disturbance types: thermal and physical 15. Thermal disturbance refers to climatic conditions that alter the extent of soil thaw and/or active layer depth (e.g., above average summer air temperatures), usually during one or multiple thaw seasons. Thermal disturbances may have little geomorphic expression on the land surface, but a measurable impact on surface water quality as sub-surface drainage connectivity changes with increased thaw and active layer depths 16-17. Physical disturbance refers to permafrost-thaw related mass movements that displace or rearrange the physical properties of the ...