Nitrous oxide and hydroxylamine measurements in the Southwest Indian Ocean

Hydroxylamine as a Potential Indicator of Nitrification in the Open Ocean

“…NH 2 OH and N 2 O Distribution NH 2 OH concentrations ranged from 2.0 to 9.5 nmol/L (MSM18/2) in the equatorial Atlantic, from 0.6 to 23.8 nmol/L (M90) in the open ocean ETSP, and from 1.5 to 20.0 nmol/L (M91) in the coastal ETSP ( Figure 2). Maximum NH 2 OH concentrations of up to 23.8 nmol/L were higher compared to the only other open ocean NH 2 OH study from Ma et al (2018) in the Southwest Indian Ocean where highest measured concentrations were 6.8 nmol/L and most concentrations were below 2 nmol/L. However, in the equatorial Atlantic and in most of the surface waters in the ETSP, NH 2 OH was indeed present in low concentrations in the surface waters.…”

“…Maximum NH 2 OH concentrations of up to 23.8 nmol/L were higher compared to the only other open ocean NH 2 OH study from Ma et al (2018) in the Southwest Indian Ocean where highest measured concentrations were 6.8 nmol/L and most concentrations were below 2 nmol/L. Except of the study from Ma et al (2018), previous NH 2 OH measurements were done without the SA solution, which could have led to an overestimation of the concentrations since NO 2 − can produce significant amounts of N 2 O through the decomposition of HNO 2 as a consequence of the acidification of the samples during FAS conversion (Kock & Bange, 2013). However, even if we only consider NH 2 OH concentrations at stations were O 2 concentrations were > 50 μmol/L, concentrations are still higher with up to 14.3 nmol/L.…”

“…General NH 2 OH Distribution in the Open OceanComparing our results from the Equatorial Atlantic and the open ocean ETSP (M90) with the results fromMa et al (2018) from the SW Indian Ocean, we find a similar relationship of 1:3 for NH 2 OH to N 2 O in all three areas for samples with O 2 concentrations >50 μmol/L Similar to the equatorial Atlantic, a significant positive correlation was also observed between NH 2 OH and N 2 O at the offshore stations pointing toward active nitrification contributing to the N 2 O accumulation in this area.3.4.…”

“…Data from the Indian Ocean are fromMa et al (2018). Data from the Indian Ocean are fromMa et al (2018).…”

“…NH 2 OH (nmol/L) versus N 2 O (nmol/L) for the equatorial Atlantic (black dots, cruise MSM 18/2), the ETSP (light gray squares, cruise M90), and the Indian Ocean (dark gray triangles) for samples with O 2 > 50 μmol/L and their regression lines. Data from the Indian Ocean are fromMa et al (2018).…”