Nitrous oxide during the onset of the Atlantic cold tongue

Abstract

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 N2O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N2O 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 N2O 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 N2O 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 N2O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N2O.

N2O Emissions From the Northern Benguela Upwelling System

“…Atmospheric N 2 O data were linearly interpolated over the time of the cruises and then used for the computation of the equilibrium concentrations, saturations, and sea-air fluxes of N 2 O. Sea-air flux densities of N 2 O (F N 2 O ) were computed as described in Arévalo-Martínez et al (2017) with instantaneous wind speeds taken from the ship's weather system (standardized to 10 m height; Garrat, 1977). N 2 O saturations (N 2 O sat ) were obtained from the concentration (C) ratio between seawater (sw) and atmospheric equilibrium (atm) values (N 2 O sat = C sw /C atm ·100).…”

“…N 2 O saturations (N 2 O sat ) were obtained from the concentration (C) ratio between seawater (sw) and atmospheric equilibrium (atm) values (N 2 O sat = C sw /C atm ·100). Sea-air flux densities of N 2 O (F N 2 O ) were computed as described in Arévalo-Martínez et al (2017) with instantaneous wind speeds taken from the ship's weather system (standardized to 10 m height; Garrat, 1977).…”

Hydroxylamine as a Potential Indicator of Nitrification in the Open Ocean

“…Additionally, Arévalo-Martínez et al (2017) showed, based on an inverse relationship between N 2 O and sea surface temperature, that N 2 O-enriched waters are transported to the surface during the upwelling season in the equatorial Atlantic. In areas like the equatorial Atlantic where nitrification is the major pathway of N 2 O formation (Arévalo-Martínez et al, 2017;Walter et al, 2006;Yoshida et al, 1989), NH 2 OH can be, therefore, interpreted as an indicator for active nitrification. Furthermore, a significant amount of oceanic N 2 O is thought to originate from archaeal rather than from bacterial nitrification (Löscher et al, 2012;Santoro et al, 2011).…”

“…However, this is the first time showing that there is a significant correlation between NH 2 OH and N 2 O in the open ocean. In areas like the equatorial Atlantic where nitrification is the major pathway of N 2 O formation (Arévalo-Martínez et al, 2017;Walter et al, 2006;Yoshida et al, 1989), NH 2 OH can be, therefore, interpreted as an indicator for active nitrification.…”

“…that were already published inArévalo-Martínez et al (2017) and complemented the data set with NH 2 OH concentrations at those four stations. We found a significant correlation between NH 2 OH and N…”