Flux of volcanic CO₂ emission estimated from melt inclusions and fluid transport modelling

Volcanic CO₂ degassing is considered the primary process that controls the global carbon cycle over geological timescales. However, fluxes of CO₂ from individual volcanoes, in particular those in past activities, have been poorly constrained. One way to estimate the flux is by using the H₂O-CO₂ systematics of melt inclusions, which, according to petrological studies, records fluxing of a deep-derived CO₂-rich fluid in the deep to shallow-level crustal magmatic systems. Assuming that this fluid fluxing is the process of volcanic CO₂ emission, we quantified the fluxes of CO₂ by combining a fluid transport model with melt inclusion data. We formulated CO₂ fluxing as an advective fluid flow in a basaltic magma column with exchanging volatiles, and applied it to the melt inclusion data from Mount Etna, the type locality of a CO₂-emitting volcano. The flux of CO₂ was calculated to be 2.4-6.0kt/day, which is consistent with the observed volcanic CO₂ emission rate of 1-10kt/day. We propose that this method potentially provides a means to quantify CO₂ emission rates in past volcanic activities. Because CO₂ fluxing is an open-system process, the estimated CO₂ emission over geological timescales evaluated with this method should give much higher values than evaluations based simply on the volume of the erupted magmas.