What do we know about Fossil Organic Carbon stock and fluxes in supergene environments?
Résumé
CO2 concentration is regulated by processes controlling the carbon fluxes occurring between different carbon pools such as atmosphere, ocean, hydrosphere, soil, biomass, and lithosphere. However, some controversies persist on the nature and quantification of carbon stocks and fluxes acting in supergene environment such as soils and rivers pools. For example, Meybeck (1993) considers that FOC released by weathering of sedimentary and metamorphic rocks can reflect up to 40-45% of POC annually carried by major rivers, instead of others numerous authors (Holland, 1978; Adams and Faure, 1996) that do not take into account this FOC yield. Up to now, at a global scale, we only know an initial estimation of the annual organic yield induced by carbonates and shales chemical weathering that reach 0.1 Gt C y-1 (Di-Giovanni et al., 2002). No FOC fluxes have been reported for chemical weathering of sands and sandstones, as well as those inherited from mechanical weathering of all sedimentary rocks, altought mechanical weathering is 4 to 11 higher than chemical one (Probst, 1992; Gaillardet, pers. com.). In addition to these gaps concerning FOC fluxes, the role of erosional processes on those of FOC in global carbon cycle (source or sink of CO2) and the FOC stock available in surficial layer of sedimentary rocks and rapidly reload in supergene carbon pools, remain unresolved.