Extreme hydrological events amplify weathering-derived inorganic carbon fluxes in the Arctic permafrost active layer

Chemical weathering plays a key role in regulating long-term atmospheric CO₂, yet the balance between CO₂-consuming and CO₂-releasing weathering pathways in Arctic catchments remains poorly constrained. Here, we present the first high-resolution, multi-decadal (1997–2022) assessment of net carbon fluxes from a heavily monitored small High Arctic river catchment in NE Greenland. Net CO₂ release is dominated by sulfuric acid weathering of carbonates driven by sulfide oxidation from pyrite minerals, as supported by δ³⁴S_SO4, δ¹⁸O_SO4, and δ¹⁸O_H2O isotopic tracers that together trace sulfide from other sulfur sources in river waters. River pH has increased by >1.5 units over the last 20+ years, consistent with progressive acid neutralisation by carbonate dissolution and coincident with progressive deepening of the active layer. 

Our results reveal intensifying sulfuric acid-carbonate weathering in response to Arctic warming and a strengthening hydrological cycle, highlighting the sensitivity of Arctic carbon fluxes to deepening of active layers, evolving flowpaths, enhanced water-rock interactions, and geomorphic disturbance. Further, we show that extreme erosional events exert contrasting controls on catchment-scale carbon fluxes: glacial lake outburst floods reduce or temporarily reverse net CO₂ release. Erosion therefore does not exert a unidirectional control on weathering-driven carbon fluxes in Arctic systems.

These findings challenge the assumption that enhanced Arctic weathering will necessarily promote long-term CO₂ sequestration and underscore the need to account for lithology-specific and process-driven controls when assessing cryosphere–carbon feedbacks under future climate change.