Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions.

We demonstrate direct eddy covariance (EC) observations of methane (CH) fluxes between the sea and atmosphere from an icebreaker in the eastern Arctic Ocean. EC-derived CH emissions averaged 4.58, 1.74, and 0.14 mg m day in the Laptev, East Siberian, and Chukchi seas, respectively, corresponding to annual sea-wide fluxes of 0.83, 0.62, and 0.03 Tg year. These EC results answer concerns that previous diffusive emission estimates, which excluded bubbling, may underestimate total emissions. We assert that bubbling dominates sea-air CH fluxes in only small constrained areas: A ~100-m area of the East Siberian Sea showed sea-air CH fluxes exceeding 600 mg m day; in a similarly sized area of the Laptev Sea, peak CH fluxes were ~170 mg m day. Calculating additional emissions below the noise level of our EC system suggests total ESAS CH emissions of 3.02 Tg year, closely matching an earlier diffusive emission estimate of 2.9 Tg year.