Global Fjords as Minor Sources of Nitrous Oxide to the Atmosphere

We report high-resolution observations of N₂O sea-air fluxes at six fjords spanning arctic, subarctic, and temperate climates. Icelandic and Swedish fjords were sources of N₂O at 97.6 ± 10.5 and 19.9 ± 19.3 μg N₂O m⁻² day⁻¹, respectively. These fjords showed increasing N₂O concentrations toward the head. In contrast, a Greenland fjord exhibited net N₂O uptake at −8.3 ± 7.8 μg N₂O m⁻² day⁻¹ with decreasing concentration toward the head of the fjord. Individual fjords appear to have unique N₂O 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 N₂O emissions. Globally, fjords release 7.9 ± 1.7 Gg N₂O yr⁻¹ to the atmosphere, which represents 2%–13% of global emissions from coastal ecosystems. These N₂O emissions offset 3.5% of CO₂ sequestration in fjords.