Methane fluxes from the sea to the atmosphere across the Siberian shelf seas

The Laptev and East Siberian Seas have been proposed as a substantial source of methane (CH4) to the atmosphere. During summer 2014, we made unique high‐resolution simultaneous measurements of CH4 in the atmosphere above, and surface waters of, the Laptev and East Siberian Seas. Turbulence‐driven sea‐air fluxes along the ship's track were derived from these observations; an average diffusive flux of 2.99 mg m−2 d−1 was calculated for the Laptev Sea and for the ice‐free portions of the western East Siberian Sea, 3.80 mg m−2 d−1. Although seafloor bubble plumes were observed at two locations in the study area, our calculations suggest that regionally, turbulence‐driven diffusive flux alone accounts for the observed atmospheric CH4 enhancements, with only a local, limited role for bubble fluxes, in contrast to earlier reports. CH4 in subice seawater in certain areas suggests that a short‐lived flux also occurs annually at ice‐out. Key Points Methane sea‐air flux in the East Siberian Arctic shelf region appears larger than other shelf seas An under‐ice accumulation of methane during ice‐covered seasons is rapidly released at ice melt Sea‐air methane flux is regionally dominated by turbulence‐driven diffusive fluxes, not bubble fluxes