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

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. (C) 2010 Elsevier B.V. All rights reserved.