Fluvial Response to a Period of Hydrometeorological Change and Landscape Disturbance in the Canadian High Arctic.

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. Plain Language Summary: The long‐term impact and response of High Arctic river systems to climate and landscape change remain poorly constrained. We investigate the effects of climate and permafrost change on sediment transport in two High Arctic rivers in Canada (75°N) during a period of rapid climate change and landscape disturbance using a 15‐year record of suspended sediment export—the longest record of its kind in the High Arctic. We find that increased sediment erosion from permafrost landscape disturbances has not increased the downstream‐suspended sediment export beyond an immediate, short‐lived response due to (1) the rivers ability to store additional sediment and (2) offsetting hydroclimatic controls. Our findings further suggest that these river systems are potentially in a transition period, shifting from a snowmelt to a rainfall dominated flow regime, but current rainfall magnitudes are below a critical threshold to mobilize additional sediment in these systems. We conclude that increased rainfall magnitude is likely to be the tipping point to significant long‐term geomorphic change and downstream effects in the Canadian High Arctic. Key Points: High Arctic fluvial systems moderate the response of increased sediment delivery from localized disturbances through in‐channel storageNival generated geomorphic energy has decreased over time, coincident with the increased importance of sporadic pluvial eventsModern rainfall magnitudes are typically below the threshold to cause widespread mobilization of additional sediment in these systems [ABSTRACT FROM AUTHOR]