Hydroxylamine as a Potential Indicator of Nitrification in the Open Ocean

Abstract

Abstract Hydroxylamine (NH2OH), a short‐lived intermediate in the nitrogen cycle, is a potential precursor of nitrous oxide (N2O) in the ocean. However, measurements of NH2OH in the ocean are sparse. Here we present a data set of depth profiles of NH2OH from the equatorial Atlantic Ocean and the eastern tropical South Pacific and compare it to N2O, nitrate, and nitrite profiles under varying oxygen conditions. The presence of NH2OH in surface waters points toward surface nitrification in the upper 100 m. Overall, we found a ratio of 1:3 between NH2OH and N2O in open ocean areas when oxygen concentrations were >50 μmol/L. In the equatorial Atlantic Ocean and the open ocean eastern tropical South Pacific, where nitrification is the dominant N2O production pathway, stepwise multiple regressions demonstrated that N2O, NH2OH, and nitrate concentrations were highly correlated, suggesting that NH2OH is a potential indicator for nitrification.