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. As climate warming and precipitation increase at high latitudes, permafrost terrains across the circumpolar north are poised for intensifiedgeomorphic activity and sediment mobilization that are expected to persist for millennia. In previously glaciated permafrost terrain, ice-richdeposits are associated with large stores of reactive mineral substrate. Over geological timescales, chemical weathering moderates atmosphericCO2 levels, raising the prospect that mass wasting driven by terrain consolidation following thaw (thermokarst) may enhance weathering ofpermafrost sediments and thus climate feedbacks. The nature of these feedbacks depends upon the mineral composition of sediments (weathering sources)and the balance between atmospheric exchange of CO2 vs. fluvial export of carbonate alkalinity (Σ[HCO3-,CO32-]). Working in the fluvially incised, ice-rich glacial deposits of the Peel Plateau in northwestern Canada, we determine theeffects of slope thermokarst in the form of retrogressive thaw slump (RTS) activity on mineral weathering sources, CO2 dynamics, andcarbonate alkalinity export and how these effects integrate across watershed scales (∼ 2 to 1000 km2). We worked along threetransects in nested watersheds with varying connectivity to RTS activity: a 550 m transect along a first-order thaw stream within a largeRTS, a 14 km transect along a stream which directly received inputs from several RTSs, and a 70 km transect along a larger streamwith headwaters that lay outside of RTS influence. In undisturbed headwaters, stream chemistry reflected CO2 from soil respirationprocesses and atmospheric exchange. Within the RTS, rapid sulfuric acid carbonate weathering, prompted by the exposure of sulfide- andcarbonate-bearing tills, appeared to increase fluvial CO2 efflux to the atmosphere and propagate carbonate alkalinity across watershedscales. Despite covering less than 1 % of the landscape, RTS activity drove carbonate alkalinity to increase by 2 orders of magnitude alongthe largest transect. Amplified export of carbonate alkalinity together with isotopic signals of shifting DIC and CO2 sources along thedownstream transects highlights the dynamic nature of carbon cycling that may typify glaciated permafrost watersheds subject to intensification ofhillslope thermokarst. The balance between CO2 drawdown in regions where carbonic acid weathering predominates and CO2 releasein regions where sulfides are more prevalent will determine the biogeochemical legacy of thermokarst and enhanced weathering in northern permafrostterrains. Effects of RTSs on carbon cycling can be expected to persist for millennia, indicating a need for their integration into predictions ofweathering–carbon–climate feedbacks among thermokarst terrains.

Thermokarst amplifies fluvial inorganic carbon cycling and export across watershed scales on the Peel Plateau, Canada