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