Methane Emissions From Seabed to Atmosphere in Polar Oceans Revealed by Direct Methane Flux Measurements

Sea-air methane flux was measured directly by the eddy-covariance method across approximately 60,000 km of Arctic and Antarctic cruises during a number of summers. The Arctic Ocean (north of 60 degrees N, between 20 degrees W and 50 degrees E) and Southern Ocean (south of 50 degrees S, between 70 degrees W and 30 degrees E) are found to be on-shelf sources of atmospheric methane with mean sea-air fluxes of 9.17 +/- 2.91 (SEM (standard error of the mean)) mu mol m-2 d-1 and 8.98 +/- 0.91 mu mol m-2 d-1, respectively. Off-shelf, this region of the Arctic Ocean is found to be a source of methane (mean flux of 2.39 +/- 0.68 mu mol m-2 d-1), while this region of the Southern Ocean is found to be a methane sink (mean flux of -0.77 +/- 0.37 mu mol m-2 d-1). The highest fluxes observed are found around west Svalbard, South Georgia, and South Shetland Islands and Bransfield Strait; areas with evidence of the presence of methane flares emanating from the seabed. Hence, this study may provide evidence of direct emission of seabed methane to the atmosphere in both the Arctic and Antarctic. Comparing with previous studies, the results of this study may indicate an increase in sea-air flux of methane in areas with seafloor seepage over timescales of several decades. As climate change exacerbates rising water temperatures, continued monitoring of methane release from polar oceans into the future is crucial. The amount of methane released from oceans into the atmosphere is uncertain. Most oceanic methane is stored in the seabed and can escape into the water at seafloor seeps, but the extent to which it escapes into the atmosphere remains unclear. This study uses a relatively new method, eddy-covariance, to measure sea-air methane fluxes during Arctic and Antarctic cruises. This is the first time this technique has been applied to sea-air methane fluxes in both polar oceans. Our findings show that on-shelf regions of the Arctic and Southern Oceans release methane into the atmosphere, with average fluxes of 9.17 +/- 2.91 mu mol m-2 d-1 and 8.98 +/- 0.91 mu mol m-2 d-1, respectively. We also identified areas with significant methane release in regions where methane has been found seeping into the water from the seabed. This study provides potential evidence that methane from seabed seeps may be directly emitted into the atmosphere in both the Arctic and Antarctic. Comparing with earlier studies, there is indication that the amount of methane released has increased over the last decades. As climate change drives increasing water temperatures, there is a potential for increased methane release from the seabed into the atmosphere, therefore on-going observations of methane release from polar oceans are necessary. Coastal regions of the Arctic Ocean and Southern Ocean are found to be sources of atmospheric methane The ocean releases elevated quantities of methane where seabed methane seeps have been observed in both the Arctic and Southern Oceans This study suggests a possible rise in methane release from oceanic areas with seabed seeps over last decades compared with a prior study