Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

Brett F. Thornton1, 2, John Prytherch2, 3, Kristian Andersson1, Ian M. Brooks4, Dominic Salisbury4, Michael Tjernström2, 3, Patrick M. Crill1, 2

1Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden.
2Bolin Centre for Climate Research, Stockholm University, 106 91 Stockholm, Sweden.
3Department of Meteorology, Stockholm University, 106 91 Stockholm, Sweden.
4School of Earth and Environment, University of Leeds, Leeds, UK.

Abstract
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.

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