Origin and fate of methane in the Eastern Tropical North Pacific oxygen minimum zone

Panagiota-Myrsini Chronopoulou, Felicity Shelley, William J Pritchard, Susanna T Maanoja, Mark Trimmer

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    Abstract

    Oxygen minimum zones (OMZs) contain the largest pools of oceanic methane but its origin and fate are poorly understood. High-resolution (<15 m) water column profiles revealed a 300 m thick layer of elevated methane (20–105 nM) in the anoxic core of the largest OMZ, the Eastern Tropical North Pacific. Sediment core incubations identified a clear benthic methane source where the OMZ meets the continental shelf, between 350 and 650 m, with the flux reflecting the concentration of methane in the overlying anoxic water. Further incubations characterised a methanogenic potential in the presence of both porewater sulphate and nitrate of up to 88 nmol g−1day−1 in the sediment surface layer. In these methane-producing sediments, the majority (85%) of methyl coenzyme M reductase alpha subunit (mcrA) gene sequences clustered with Methanosarcinaceae (greater than or equal to96% similarity to Methanococcoides sp.), a family capable of performing non-competitive methanogenesis. Incubations with 13C-CH4 showed potential for both aerobic and anaerobic methane oxidation in the waters within and above the OMZ. Both aerobic and anaerobic methane oxidation is corroborated by the presence of particulate methane monooxygenase (pmoA) gene sequences, related to type I methanotrophs and the lineage of Candidatus Methylomirabilis oxyfera, known to perform nitrite-dependent anaerobic methane oxidation (N-DAMO), respectively.
    Original languageEnglish
    Pages (from-to)1386–1399
    Number of pages14
    JournalISME Journal
    Volume11
    Early online date28 Feb 2017
    DOIs
    Publication statusPublished - 2017
    Publication typeA1 Journal article-refereed

    Publication forum classification

    • Publication forum level 3

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