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

• Published in: Global biogeochemical cycles 2022-04, Vol.36 (4), p.n/a
• Main Authors: Manning, Cara C. M., Zheng, Zhiyin, Fenwick, Lindsay, McCulloch, Ross D., Damm, Ellen, Izett, Robert W., Williams, William J., Zimmermann, Sarah, Vagle, Svein, Tortell, Philippe D.
• Format: Article
• Language: English
• Subjects: Arctic Ocean; biogeochemistry; Climate change; Consumption; Depletion; Emissions; Future climates; Gases; Greenhouse effect; Greenhouse gases; Interannual variability; Isotopes; Methane; Nitrous oxide; Oceans; Oxidation; Ozone; Ozone depletion; Ozone layer; Ozonosphere; Polar regions; Rivers; Sediment; Sediments; Summer; Synopsis; Variability; Water circulation; Water column
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1029/2021GB007185

Between 2015 and 2018, we collected approximately 2,000 water column measurements of methane (CH4) and nitrous oxide (N2O) concentrations in the North American Arctic Ocean during summer and early fall. We also obtained 25 measurements of CH4 and N2O concentrations in rivers along the Northwest Passage and Ellesmere Island in midsummer 2017–2019. Our results show that N2O is generated in the highly productive Bering and Chukchi Seas and transported northeastward, producing a persistent subsurface N2O peak in the Beaufort Sea. The Chukchi and Beaufort Sea sediments are a significant source of CH4 to the water column. These sedimentary sources and associated water column consumption display significant spatial gradients and interannual variability. CH4 isotope data demonstrate the importance of CH4 oxidation across the study region. We find that rivers are not a significant source of CH4 or N2O to the Arctic Ocean at the time of year sampled. The estimated annual sea‐air flux across the study region (2.3 million km2) had a median (first quartile, third quartile) of 0.009 (0.002, 0.023) Tg CH4 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 CH4 and N2O budgets. Our expansive data set, with observations at many repeat stations, provides a synopsis of present‐day Arctic CH4 and N2O distributions and their range of variability, as well as a benchmark against which future climate‐dependent changes can be evaluated. Plain Language Summary Methane (CH4) and nitrous oxide (N2O) are powerful greenhouse gases, and N2O contributes to the depletion of the ozone layer. Rapid warming could change Arctic emissions of CH4 and N2O. To date, most Arctic studies of CH4 and N2O have focused on small geographic regions and/or not involved repeat observations across multiple years. To address these limitations, we collected approximately 2,000 measurements of CH4 and N2O across the North American Arctic Ocean between 2015 and 2018 in summer and early fall, including many repeat stations. We show that N2O is produced in the Bering and Chukchi Seas and transported eastward into the Beaufort Sea. The Chukchi and Beaufort Sea sediments are a considerable source of CH4 to the water column. These sedimentary sources and the associated water column consumption display significant variability. We collected river measurements between 2017 and 2019, which demonstrated that rivers are not a subst