Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry

Roland, M.; Serrano-Ortiz, P.; Kowalski, A. S.; Goddéris, Y.; Sánchez-Cañete, E. P.; Ciais, P.; Domingo, F.; Cuezva, S.; Sanchez-Moral, S.; Longdoz, B.; Yakir, D.; Van Grieken, R.; Schott, J.; Cardell, C.; Janssens, I. A.

CO 2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO 2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or nighttime CO 2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO 2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO 2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO 2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO 2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO 2 exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO 2 during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO 2 production. At night, ventilation ceases and the depleted CO 2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO 2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil–atmosphere CO 2 exchanges in dry regions \mbox{with carbonate soils}.

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Roland, M. / Serrano-Ortiz, P. / Kowalski, A. S. / et al: Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry. 2013. Copernicus Publications.

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