A study on the gechemical processes that control the production and the consumption of atmospheric CO2 in Alpine region

On geological time-scales the CO2 fluxes from the solid Earth to the atmosphere mainly result from volcanism and metamorphic-decarbonation processes, while the CO2 fluxes from atmosphere to solid Earth mainly depend on silicate and carbonate weathering, biogenic precipitation and removal of CaCO3 and volcanic gases - seawater interactions. We show a balance for Alpine region between CO2 fixed by weathering and CO2 emitted by springs. The dissolved load of streams originates from rain, pollution, evaporite dissolution, silicate and carbonate weathering. We quantified each contributions for 33 sampled rivers. Depending on time-scales we used different equations to quantificate the CO2 fixed by weathering. The CO2 production was estimated from a database with composition of more than 1000 springs (both data from litterature and new data). For each point through an isotopic and mass balance approach we estimated: Ccarb (carbon from carbonate dissolution), Cinf (atmospheric and biogenic CO2) and Cdeep (CO2 from deep degassing). For each spring the flux of deep CO2 is given by Cdeep X Q/A, (Q: flow rate, A: recharge area), or by Cdeep X IE, (IE: effective infltration, IE=Q/A). IE have been estimated using a water balance model. The results shows: deep-CO2 rich springs are located along the more important Alpine tectonic structures and in the basins external to the Alps, Alpine chain at the present seems to be a sink for atmospheric CO2 but it is probably a source on long term.