Global Fjords as Minor Sources of Nitrous Oxide to the Atmosphere

Abstract We report high‐resolution observations of N 2 O sea‐air fluxes at six fjords spanning arctic, subarctic, and temperate climates. Icelandic and Swedish fjords were sources of N 2 O at 97.6 ± 10.5 and 19.9 ± 19.3 μg N 2 O m −2 day −1 , respectively. These fjords showed increasing N 2 O concentrations toward the head. In contrast, a Greenland fjord exhibited net N 2 O uptake at −8.3 ± 7.8 μg N 2 O m −2 day −1 with decreasing concentration toward the head of the fjord. Individual fjords appear to have unique N 2 O drivers such as temperature, salinity, chlorophyll, and pH but no overarching driver was identified across all fjords. In Icelandic and Swedish fjords, low oxygen in subsurface waters and aquaculture activities may have enhanced N 2 O emissions. Globally, fjords release 7.9 ± 1.7 Gg N 2 O yr −1 to the atmosphere, which represents 2%–13% of global emissions from coastal ecosystems. These N 2 O emissions offset 3.5% of CO 2 sequestration in fjords.