SOurces and SInks of the CO2 soil Emissions in active and quiescent volcanoes – SOSIE

The SOSIE project will quantify the budget and identify the causes of the temporal and spatial variability of diffuse volcanic CO2 emissions. Diffuse CO2 emissions from the soil over large volcanic regions represent more than the emissions from permanently degassing craters and during eruptions. Between the deep magmatic source and the surface, processes of accumulation, sequestration and remobilization of CO2 in the subsurface, the hydrosphere, the soil and the biosphere complicate the spatial and temporal distribution of these emissions and currently constitute a major scientific barrier in the understanding of the carbon cycle and geochemical volcano monitoring. We will address this problem with comprehensive approach to the evolution and transfer of magmatic fluids based on a chemical, mineralogical and biological study of reference sites located in the Indian Ocean covering a very wide range of volcanic, tectonic, environmental settings and CO2 flux and geochemical signatures. The project thus targets both tropical (La Reunion, Mayotte) and subpolar (Kerguelen) contexts, on volcanoes with variable eruptive dynamics and magmatic plumbing systems. The project also addresses for the first time the origin of negative flow sites whose origin remains unclear and which could constitute major natural carbon sinks. By highlighting processes governing the mobility of carbon in different geological reservoirs, the project will, on the one hand, highlight new possible carbon sequestration and remobilization mechanisms and, on the other hand, improve the interpretation of geochemical time series for monitoring volcanic and seismic activity.