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

Abstract

Abstract. The chemical weathering of minerals is a primary control on atmospheric CO2 levels and Earth's climate over geological timescales. As climate warming and precipitation intensify at high latitudes, glaciated terrains across the circumpolar north are poised for rapid geomorphic change and associated changes in mineral weathering dynamics. Here, we determine how the effects of permafrost thaw on mineral weathering sources and inorganic carbon cycling and export integrate across watershed scales (from ~ 2 to 1000 km2) in a permafrost terrain within a former glacial margin and dominated by relatively inorganic sediments (Peel Plateau, Canada). Our work was conducted along three nested transects with varying intensities of retrogressive thaw slump (RTS) thermokarst activity: a 550 m transect along a first-order thaw stream within a RTS; a 14 km transect along a stream which directly received RTS inputs; and a 70 km transect along a larger stream which received inputs from RTS-affected tributaries. In the thaw stream, rapid sulfuric acid weathering of carbonate tills appeared to amplify CO2 efflux to the atmosphere and HCO3− export downstream, where DIC and CO2 stable isotopes revealed a shift to an abiotic-inorganic driven aquatic carbon cycle. Along the intermediate transect, DIC concentrations were ten times higher in the RTS-affected reach than in the undisturbed headwaters, and decreased downstream with decreasing RTS area. Along the largest transect, HCO3− concentrations increased by two orders of magnitude in association with RTS activity, despite RTSs covering only ~ 0.5 % of the landscape. Statistical modeling of hydrochemical measurements and geospatial landscape data showed that RTSs were a primary landscape driver of HCO3− export across watershed scales. Constraining sources and rates of mineral weathering across diverse permafrost terrains will help to understand future changes in Arctic aquatic carbon cycling, as our results suggest that abiotic-inorganic processes may become prevalent.