Sources and sinks of N2O in the subpolar and polar North Atlantic

The Arctic Ocean is particularly sensitive to climate change. Its ecosystem structure and function are prone to be disturbed by fast warming and massive retreat of sea-ice, which in turn, might result in feedbacks on climate. Moreover, such drastic changes are expected to influence the meridional fluxes of heat, freshwater and biogeochemical tracers between subpolar areas and the Arctic. As the third most important greenhouse gas and major ozone-depleting substance in the stratosphere, nitrous oxide (N₂O) is a crucial gas to study in order to assess the ocean’s role in the production and exchange of climate-relevant compounds to the atmosphere. Between 2018 and 2019 we conducted ship-based surveys to elucidate the source-sink dynamics of N₂O in the subpolar-polar North Atlantic. Based on results from those campaigns, we show the distribution and spatial variability of surface N₂O, which ranged from moderate supersaturation (positive sea-air fluxes) in ice-free subpolar areas to unusually strong undersaturation (negative sea-air fluxes) in partially or fully ice-covered areas. We also present a comprehensive overview of the water column distribution of N₂O in the region, and by combining this data with hydrographic and chemical (O₂ and inorganic nutrients) information, we trace back the origin of the dominant water masses so as to illustrate the connectivity between the Fram Strait and the Nordic Seas off southeast Greenland. This analysis is used to discuss how the meridional water mass exchange in the region influences the balance of local vs. remote N₂O production and its spatial variability. Furthermore, we use the results from collocated molecular analyses (functional gene markers) to infer the occurrence and abundances of the main microbial communities responsible for the cycling of N₂O. This contribution is relevant for assessments of expected changes in trace gas emissions with further climate-driven changes in the Arctic Ocean.