Interannual Variability in Methane and Nitrous Oxide Concentrations and Sea‐Air Fluxes Across the North American Arctic Ocean (2015–2019)

Between 2015 and 2018, we collected approximately 2,000 water column measurements of methane (CH 4 ) and nitrous oxide (N 2 O) concentrations in the North American Arctic Ocean during summer and early fall. We also obtained 25 measurements of CH 4 and N 2 O concentrations in rivers along the Northwest Passage and Ellesmere Island in midsummer 2017–2019. Our results show that N 2 O is generated in the highly productive Bering and Chukchi Seas and transported northeastward, producing a persistent subsurface N 2 O peak in the Beaufort Sea. The Chukchi and Beaufort Sea sediments are a significant source of CH 4 to the water column. These sedimentary sources and associated water column consumption display significant spatial gradients and interannual variability. CH 4 isotope data demonstrate the importance of CH 4 oxidation across the study region. We find that rivers are not a significant source of CH 4 or N 2 O to the Arctic Ocean at the time of year sampled. The estimated annual sea‐air flux across the study region (2.3 million km 2 ) had a median (first quartile, third quartile) of 0.009 (0.002, 0.023) Tg CH 4 y −1 and −0.003 (−0.013, 0.010) Tg N y −1 . These results suggest that the North American Arctic Ocean currently plays a negligible role in global CH 4 and N 2 O budgets. Our expansive data set, with observations at many repeat stations, provides a synopsis of present‐day Arctic CH 4 and N 2 O distributions and their range of variability, as well as a benchmark against which future climate‐dependent changes can be evaluated.