Nitrous oxide (N2O) is a powerful greenhouse gas, and oceanic sources account for up to one third of the total natural flux to the atmosphere. In oxygen‐deficient zones (ODZs) like the Eastern Tropical North Pacific (ETNP), N2O can be produced and consumed by several biological processes. In this study, the concentration and isotopocule ratios of N2O from a 2016 cruise in the ETNP were analyzed to examine sources of and controls on N2O cycling across this region. Along the north‐south transect, three distinct biogeochemical regimes were identified: background, core‐ODZ, and high‐N2O stations. Background stations were characterized by smaller variations in N2O concentration and isotopic profiles relative to the other regimes. Core‐ODZ stations were characterized by co‐occurring N2O production and consumption at anoxic depths, indicated by high δ18O‐N2O (>90‰) and low δ15N2Oβ(<−10‰) values, and confirmed by a time‐dependent model, which indicated that N2O production via denitrification was significant and may occur with a nonzero site preference. High‐N2O stations, located at the periphery of a mesoscale eddy, were defined by N2O reaching 126.07 ± 12.6 nM and low oxygen concentrations expanding into near‐surface isopycnals. At these stations, model results indicated significant N2O production from ammonia‐oxidizing archaea and denitrification from nitrate at the N2O maximum within the oxycline, while bacterial nitrification and denitrification from nitrite were insignificant. This study also represents the first in the ETNP to link N2O production mechanisms to a mesoscale eddy through isotopocule measurements, suggesting the importance of eddies to spatiotemporal variability in N2O cycling and emissions from this region.
Marine oxygen‐deficient zones represent a natural source of nitrous oxide (N2O), a potent greenhouse gas and ozone‐depleting agent. To investigate controls on N2O production, the responses of ammonia oxidation (AO) to nitrite () and N2O with respect to oxygen (O2), ammonium () and concentrations were evaluated using tracer incubations in the Eastern Tropical North Pacific. Within the oxycline, additions of and O2stimulated N2O production according to Michaelis–Menten kinetics, indicating that both substrates were limiting, and that N2O production, even if the exact mechanisms remain uncertain, is mediated by predictable kinetics. Low half‐saturation constants for (12–28 nM) and O2(460 ± 130 nM) during N2O production indicate that AO communities are well adapted to low concentrations of both substrates. Hybrid N2O formation (i.e., from one and one unlabeled nitrogen (N) source, e.g., , NO) accounted for ~ 90% of the N2O production from and was robust across the different O2, , and conditions. Lack of response to variable substrate concentrations implies that the unlabeled N source was not limiting for N2O production. Although both O2and were key modulators of N2O production rates, N2O yield (N2O produced per produced) seemed to be controlled solely by O2. The N2O yield increased when O2concentrations dropped below the half‐saturation concentration for AO to (< 1.4
- NSF-PAR ID:
- 10397069
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 68
- Issue:
- 2
- ISSN:
- 0024-3590
- Format(s):
- Medium: X Size: p. 424-438
- Size(s):
- p. 424-438
- Sponsoring Org:
- National Science Foundation
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