Geology

Organic chemistry

Oceanography

Chemistry

Earth science

Climatology

Environmental science

Methane

Nature Geoscience

Anaerobic oxidation of methane provides a globally important, yet poorly constrained barrier for the vast amounts of methane produced in the subseafloor. Here we provide a global map and budget of the methane flux and degradation in diffusion-controlled marine sediments in relation to the depth of the methane oxidation barrier. Our new budget suggests that 45–61 Tg of methane are oxidized with sulfate annually, with approximately 80% of this oxidation occurring in continental shelf sediments (&lt;200 m water depth). Using anaerobic oxidation as a nearly quantitative sink for methane in steady-state diffusive sediments, we calculate that ~3–4% of the global organic carbon flux to the seafloor is converted to methane. We further report a global imbalance of diffusive methane and sulfate fluxes into the sulfate–methane transition with no clear trend with respect to the corresponding depth of the methane oxidation barrier. The observed global mean net flux ratio between sulfate and methane of 1.4:1 indicates that, on average, the methane flux to the sulfate–methane transition accounts for only ~70% of the sulfate consumption in the sulfate–methane transition zone of marine sediments. Much of the methane produced by the deep subseafloor biosphere is consumed by anaerobic methane oxidation with sulfate in continental shelf sediments, according to a global map and calculated budgets of methane fluxes and degradation.

Global diffusive fluxes of methane in marine sediments