Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

We demonstrate direct eddy covariance (EC) observations of methane (CH₄) fluxes between the sea and atmosphere from an icebreaker in the eastern Arctic Ocean. EC-derived CH₄ emissions averaged 4.58, 1.74, and 0.14 mg m^-2 day^-1 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^-1. These EC results answer concerns that previous diffusive emission estimates, which excluded bubbling, may underestimate total emissions. We assert that bubbling dominates sea-air CH₄ fluxes in only small constrained areas: A ~100-m² area of the East Siberian Sea showed sea-air CH₄ fluxes exceeding 600 mg m^-2 day^-1; in a similarly sized area of the Laptev Sea, peak CH₄ fluxes were ~170 mg m^-2 day^-1. Calculating additional emissions below the noise level of our EC system suggests total ESAS CH₄ emissions of 3.02 Tg year^-1, closely matching an earlier diffusive emission estimate of 2.9 Tg year^-1.