title: Origin and fate of methane in the Eastern Tropical North Pacific oxygen minimum zone.
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-1in 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 (⩾96% similarity to Methanococcoides sp.), a family capable of performing non-competitive methanogenesis. Incubations with13C-CH4showed 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.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Panagiota-Myrsini
authors.initials: PM
authors.lastname: Chronopoulou
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Felicity
authors.initials: F
authors.lastname: Shelley
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: William J
authors.initials: WJ
authors.lastname: Pritchard
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Susanna T
authors.initials: ST
authors.lastname: Maanoja
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Trimmer
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001419:Bacteria / Q000235:genetics*; D008697:Methane / Q000737:chemistry*; D009566:Nitrates; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D010140:Pacific Ocean; D012623:Seawater / Q000737:chemistry* / Q000382:microbiology; D014871:Water Microbiology
chemical_list: D009566:Nitrates; D010105:Oxygenases; C021555:methane monooxygenase; D008697:Methane; D010100:Oxygen