Volcanic CO₂ flux into the atmosphere

Marie Edmonds (Cambridge University)

Volcanoes are a primary mechanism for the transfer of carbon from the interior of Earth (mantle and crust) to the surface environment. Over Earth history, volcanic outgassing has played a central role in setting the atmospheric concentration of CO₂. Quantifying the magnitude of the volcanic CO₂ flux in the present day is a significant challenge. Over the past 10 years important advances have been made in instrumentation to measure and monitor volcanic CO₂, and recently the very first observations of volcanic CO₂ from space were published. The magnitude of the volcanic CO₂ flux into the atmosphere in the present day can now be estimated, although significant uncertainties remain. The data reveal that the volcanic CO₂ flux is a small fraction (of the order of 1%) of the estimated anthropogenic flux of CO₂ into the atmosphere. Long term datasets at individual volcanoes reveal that the CO₂ flux may be highly variable with time. There are a few volcanoes and volcanic regions that dominate the volcanic CO₂ flux, including large continental volcanic centres such as Yellowstone (USA) and Mount Etna (Italy).  The isotopic composition of the carbon tells us about carbon provenance: arc volcanoes outgas carbon that is isotopically heavier than typical mantle values and is derived partly from the subducting slab, and partly from the assimilation of limestones in the crust. Over geological time, it is likely that the relative importance of continental volcanoes would have waxed and waned, with implications for both the atmospheric concentration of CO₂ and the isotopic composition of Earth’s surface reservoir.