Methane (CH₄) in the ocean is to a large extend consumed by microorganisms. During anaerobic decay within the sea floor, microbes convert methane with the help of sulphate (SO₄^2-). This process produces hydrogen sulphide anions (HS^-) and hydrogen sulphide (H₂S), which are closely related chemically and occur naturally together, as well as bicarbonate (CaCO₃). Bicarbonate can react with calcium ions (Ca²⁺) to precipitate as calcium carbonate (CaCO₃). During aerobic decay (in the water column) oxygen (O₂) from the water is consumed. Carbon dioxide (CO₂) and water (H₂O) are produced. If large amounts of methane are released in the future from the gas hydrates in the sea floor, aerobic decay could result in the creation of oxygen minimum zones. The carbon dioxide produced could also contribute to ocean acidification.

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