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.
