Iron-Coupled Anaerobic Oxidation of Methane in Marine Sediments: A Review

Anaerobic oxidation of methane (AOM) is one of the major processes of oxidizing methane in marine sediments. Up to now, extensive studies about AOM coupled to sulfate reduction have been conducted because SO42- is the most abundant electron acceptor in seawater and shallow marine sediments. However, other terminal electron acceptors of AOM, such as NO3-, NO2-, Mn(IV), Fe(III), are more energetically favorable than SO42-. Iron oxides, part of the major components in deep marine sediments, might play a significant role as an electron acceptor in the AOM process, mainly below the sulfate-methane interface, mediated by physiologically related microorganisms. Iron-coupled AOM is possibly the dominant non-sulfate-dependent AOM process to consume methane in marine ecosystems. In this review, the conditions for iron-coupled AOM are summarized, and the forms of iron oxides as electron acceptors and the microbial mechanisms are discussed.