Nitrous oxide and hydroxylamine measurements in the Southwest Indian Ocean

Abstract

The southwestern basin of the Indian Ocean (SWIO) remains a rather under-sampled region with regard to nitrogen-cycle processes. Here we present the results of extensive nitrous oxide (N2O) measurements as well as the first reported open ocean measurements of hydroxylamine (NH2OH). Enhanced N2O sea-to-air fluxes were found in the zonal band between 5°S and 10°S as a result of wind-driven upwelling, and N2O depth profiles showed supersaturation throughout the water column with a distinct maximum at about 1000 m. Excess N2O (ΔN2O) was found to be positively correlated with apparent oxygen utilization (AOU) and nitrate. Although the water column distribution of NH2OH was highly variable, combined analysis with N2O and nutrient data allows us to argue for nitrification as the major formation pathway of N2O in the SWIO. © 2018 Elsevier B.V.