Nitrous oxide variability at sub-kilometre resolution in the Atlantic sector of the Southern Ocean

The Southern Ocean is an important region for global nitrous oxide (N 2 O) cycling. The contribution of different source and sink mechanisms is, however, not very well constrained due to a scarcity of seawater data from the area. Here we present high-resolution surface N 2 O measurements from the Atlantic sector of the Southern Ocean, taking advantage of a relatively new underway setup allowing for collection of data during transit across mesoscale features such as frontal systems and eddies. Covering a range of different environments and biogeochemical settings, N 2 O saturations and sea-to-air fluxes were highly variable: Saturations ranged from 96.5% at the sea ice edge in the Weddell Sea to 126.1% across the Polar Frontal Zone during transit to South Georgia. Negative sea-to-air fluxes (N 2 O uptake) of up to −1.3 µmol m −2 d −1 were observed in the Subantarctic Zone and highest positive fluxes (N 2 O emission) of 14.5 µmol m −2 d −1 in Stromness Bay, coastal South Georgia. Although N 2 O saturations were high in areas of high productivity, no correlation between saturations and chlorophyll a (as a proxy for productivity) was observed. Nevertheless, there is a clear effect of islands and shallow bathymetry on N 2 O production as inferred from supersaturations.