Oral

IACS

C05 - Cryospheric biogeochemical cycles and environmental effects

An Unbalancing Act of Sulfuric Acid Weathering in Glacial Carbon Cycling

Biogeochemical reactions within glacier environments may exert a considerable influence on the global carbon cycle, potentially generating feedbacks that modulate planetary climate dynamics. The precise net CO2 impact of glacier weathering remains a complex and somewhat unresolved question, primarily due to the intricate interplay of counteracting weathering processes. In this study, we present a comprehensive investigation into glacier meltwater chemistry across regional to global scales, designed to elucidate the diverse combinations of weathering reactions that collectively determine the glacial CO2 source-sink dynamic. In contrast to prior assessments largely focused on silicate weathering in isolation, our data-driven framework, leveraging a substantial dataset of 850 meltwater samples from nine globally distributed mountain ranges, with a particular emphasis on High Mountain Asia, suggests the existence of regionally distinct weathering reaction combinations. Our analysis tentatively identifies two primary weathering modes: silicate-dominated regimes, which appear to be characterized by net CO2 uptake from the atmosphere, and sulfide-oxidation-dominated regimes, which seem to exhibit net CO2 release, with precipitation variability potentially acting as a secondary modulator of these modes. We observed that sulfuric acid, derived from pyrite oxidation, interlinks these modes, likely by enhancing carbonate mineral dissolution while leaving silicate weathering kinetics comparatively unaffected. These regionally varying weathering modes, seemingly governed by the integrated lithology-water chemistry nexus, may have distinct implications for regional CO2 balancing and could potentially leave discernible hydrochemical signatures within proglacial systems. Overall, this work aims to provide a systematic and simplified conceptual framework for better understanding the complex function and regionally expressed variability of glacier weathering within the broader context of global biogeochemical cycles and their climatic implications.