Ma, Xiao, Bange, Hermann W. , Eirund, Gesa K. and Arévalo-Martínez, Damian L. (2020) Nitrous oxide and hydroxylamine measurements in the Southwest Indian Ocean. Journal of Marine Systems, 209 . Art.Nr. 103062. DOI 10.1016/j.jmarsys.2018.03.003.

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Abstract

Highlights:
• Enhanced surface N2O saturations were found between 5°S and 10°S in the SWIO.
• The SWIO was a rather weak source of N2O to the atmosphere.
• A distinct N2O maximum was found at about 1000 m.
• The distributions of NH2OH in the water column were highly variable.
• Nitrification was the major formation pathway of N2O in the SWIO.

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.

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