Philippe D. Tortell

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.