Abstract
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.
Highlights
IntroductionIron-Coupled Anaerobic Oxidation of Methane is the second most powerful anthropogenic greenhouse gas in the atmosphere, after carbon dioxide, and it plays an important role in marine and atmospheric chemistry [1]
Iron-Coupled Anaerobic Oxidation of Methane is the second most powerful anthropogenic greenhouse gas in the atmosphere, after carbon dioxide, and it plays an important role in marine and atmospheric chemistry [1].Considered on an equivalent mass basis, methane, which has a relative global warming potential of 265, 34 times higher than that of CO2 present in the atmospheric environment, contributes to 16% of global warming [2,3,4]
Fe-anaerobic oxidation of methane (AOM) in the marine sediments has been identified by the elevated concentrations of dissolved iron in the methanic zone
Summary
Iron-Coupled Anaerobic Oxidation of Methane is the second most powerful anthropogenic greenhouse gas in the atmosphere, after carbon dioxide, and it plays an important role in marine and atmospheric chemistry [1]. Due to a large amount of sulfate in the oceanic ecosystem, sulfate reduction coupled AOM (as shown in Equation (1)), which can be conducted only via microbes, is considered the major AOM process in marine sediments and has been a subject of intense investigation for decades [8,9]. All the above implies that iron-coupled AOM (Fe-AOM) might play an important role in marine methane oxidization and might have been underestimated, especially in sulfate-depleted environments [11,12]. Sulfate-dependent AOM is considered to be the most significant process for methane consumption, especially for marine ecosystems, AOM via iron reduction is reported to occur in some marine and freshwater environments with depleted sulfate and nitrate [13]. The studies pertaining to the conditions, microbiology, and geochemistry of Fe-AOM are summarized, and the environmental significance of Fe-AOM and challenges for future research are discussed
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