Global gas flux from mud volcanoes: A significant source of fossil methane in the atmosphere and the ocean

[1] There are yet unidentified sources of fossil methane (CH4) in the atmosphere. Mud volcanoes (MVs) are a potentially significant but poorly quantified geologic source of fossil hydrocarbon gases and CO2 to the atmosphere and the ocean not included in the current models of sources and sinks. Our statistical analysis of 36 previous measurements and estimates of gas flux from individual MVs suggests that the global gas flux may be as high as similar to33 Tg yr(-1) (similar to15.9 Tg yr(-1) during quiescent periods plus similar to17.1 Tg yr(-1) during eruptions). Onshore and shallow offshore MVs are estimated to contribute similar to6 Tg yr(-1) of greenhouse gases directly to the atmosphere. MVs may contribute similar to9% of fossil CH4 missing in the modern atmospheric CH4 budget, and similar to12% in the preindustrial budget. Large volumes (similar to27 Tg yr(-1)) of gas may escape from deep-water MVs, suggesting that global gas flux from the seafloor may be underestimated.