Nitrous oxide during the onset of the A tlantic cold tongue

The tropical Atlantic exerts a major influence in climate variability through strong air‐sea interactions. Within this region, the eastern side of the equatorial band is characterized by strong seasonality, whereby the most prominent feature is the annual development of the Atlantic cold tongue (ACT). This band of low sea surface temperatures (∼22–23°C) is typically associated with upwelling‐driven enhancement of surface nutrient concentrations and primary production. Based on a detailed investigation of the distribution and sea‐to‐air fluxes of N 2 O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N 2 O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring‐summer. We observed a strong influence of the surface currents of the EEA on the N 2 O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward‐flowing North Equatorial Countercurrent and the cold westward‐flowing South Equatorial Current. Estimated sea‐to‐air fluxes of N 2 O from the ACT (mean 5.18 ± 2.59 μmol m −2 d −1 ) suggest that in May–July 2011 this cold‐water band doubled the N 2 O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N 2 O.