Climate forcing controls on carbon terrestrial fluxes during shale weathering
Abstract
Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO<sub>2</sub>) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO<sub>2</sub> (1.02 mol C/m<sup>2</sup>/y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO<sub>2</sub> drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO<sub>2</sub> flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m<sup>2</sup>/y). We show that shale CO<sub>2</sub> consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO<sub>2</sub> transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO<sub>2(g)</sub> egress patterns and thus must be considered when inferring soil CO<sub>2</sub> drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO<sub>2</sub> sink.
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Cited By (16 times, 2 in Knowledge Hub)
References (64)
9 in Knowledge Hub, 55 external