The missing carbon budget puzzle piece: shallow-water hydrothermal vents contribution to global CO2 fluxes

The release of CO2 gases from volcanoes and their secondary geothermal manifestations are an important contributor to the global carbon budget. While degassing from mid ocean ridges is relatively well-constrained, the contribution of shallow submarine volcanic degassing to the atmosphere is less clear. Shallow-water hydrothermal vents are common seafloor features present at depths shallower than 200 m near submarine volcanic areas, releasing a gas phase composed mainly of CO2 mixed with other trace gases. Despite their widespread distribution, a limited number of studies have investigated shallow-water vents CO2 flux to the atmosphere. Based on available data and through three different data expansion techniques, we estimate that shallow-water hydrothermal vents can contribute between 20 and 128 Mt CO2 yr-1 globally, increasing previous estimates of global volcanic CO2 fluxes by ~9 to ~22 %. We conclude that shallow-water hydrothermal vents might be a significant, yet neglected contributor to the global carbon budget, and systematic studies are needed to increase the data available and better constrain their carbon contribution to the atmosphere.