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Hidden, abiotic CO₂ flows and gaseous reservoirs in the terrestrial carbon cycle: Review and perspectives

Serrano-Ortiz, Penélope, Roland, Marilyn, Sanchez-Moral, Sergio, Janssens, Ivan A., Domingo, Francisco, Goddéris, Yves, Kowalski, Andrew S.
Agricultural and forest meteorology 2010 v.150 no.3 pp. 321-329
carbon dioxide, biogeochemical cycles, carbon sequestration, soil weathering, calcite, precipitation, soil chemistry, geochemistry, simulation models, gas emissions, deserts, temporal variation, seasonal variation, caves, gas exchange, net ecosystem exchange
This review article analyzes different abiotic processes that could contribute to the global carbon cycle on short time scales, beginning with high rates of net CO₂ release or uptake measured over ecosystems by the FLUXNET community. The two main abiotic interpretations for these “anomalous” measurements are weathering processes and subterranean cavity ventilation. After analyzing their mechanisms and drivers, we evaluate their possible relevance and contributions in the studies mentioned above. Analyzing weathering (calcite dissolution and precipitation) chemistry and using a geochemical model, we conclude that CO₂ dissolution processes could explain the measured CO₂ release following dry season rain events, but their contribution is far from sufficient to explain large magnitudes of daytime CO₂ emissions or annual CO₂ uptake measured in some desert ecosystems. In this context, we hypothesize and evaluate a further abiotic mechanism: the role of subterranean cavities as a temporal depot of CO₂, along with their seasonal ventilation. A first approximation estimates that the subterranean CO₂ pool (and its potential ventilation) could represent more than half of the total CO₂ content of the atmosphere. Therefore, the non-negligible potential contribution to the net ecosystem carbon balance requires further investigation towards a better understanding of its drivers.