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^◦N, between 20^◦W and 50^◦E) and Southern Ocean (south of 50^◦S, between 70^◦W and 30^◦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)) µmol m⁻² d⁻¹ and 8.98 ± 0.91 µmol 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 µmol 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 µmol 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.