Pelagic methane oxidation in the northern Chukchi Sea

Significant amounts of methane reside in sediments along the continental margins and slope of the Arctic Ocean. Methanotrophic bacteria oxidize methane to bicarbonate and also assimilate some methane-derived carbon into biomass. Their metabolism transforms methane to other forms of carbon and sequesters it within the system, reducing its emission to the atmosphere. Increases in water temperatures driven by global climate change may accelerate the methane flux from the benthos into the water column, potentially increasing the importance of methanotrophic consumption as a methane sink. We report methane concentrations and oxidation rates in the water column of the Chukchi Sea from August 2017. This area is characterized by seasonally high nutrient concentrations that fuel high rates of pelagic primary productivity and subsequent sedimentation of organic matter, which stimulates benthic methanogenesis. Methane concentrations in the study area ranged from 6 to 72 nmol L-1, consistent with previously published measurements. Methane oxidation rates were as high as 580 pmol L-1 d(-1), similar to the rates measured in the East Siberian Arctic Shelf. Depth-integrated methane oxidation rates were lower than methane efflux rates, suggesting that physiochemical factors prevent the methanotrophic microbial community from efficiently removing methane from the ecosystem. Still, methanotrophic bacteria provide an ecosystem service by removing a fraction of methane prior to its efflux to the atmosphere.