N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment

dc.contributor.author Bourbonnais, Annie
dc.contributor.author Altabet, Mark A.
dc.contributor.author Charoenpong, Chawalit N.
dc.contributor.author Larkum, Jennifer
dc.contributor.author Hu, Haibei
dc.contributor.author Bange, Hermann W.
dc.contributor.author Stramma, Lothar
dc.date.accessioned 2015-08-18T17:29:03Z
dc.date.available 2015-12-06T09:27:18Z
dc.date.issued 2015-06-06
dc.description Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 29 (2015): 793-811, doi:10.1002/2014GB005001. en_US
dc.description.abstract Mesoscale eddies in Oxygen Minimum Zones (OMZs) have been identified as important fixed nitrogen (N) loss hotspots that may significantly impact both the global rate of N-loss as well as the ocean's N isotope budget. They also represent “natural tracer experiments” with intensified biogeochemical signals that can be exploited to understand the large-scale processes that control N-loss and associated isotope effects (ε; the ‰ deviation from 1 in the ratio of reaction rate constants for the light versus heavy isotopologues). We observed large ranges in the concentrations and N and O isotopic compositions of nitrate (NO3−), nitrite (NO2−), and biogenic N2 associated with an anticyclonic mode-water eddy in the Peru OMZ during two cruises in November and December 2012. In the eddy's center where NO3− was nearly exhausted, we measured the highest δ15N values for both NO3− and NO2− (up to ~70‰ and 50‰) ever reported for an OMZ. Correspondingly, N deficit and biogenic N2-N concentrations were also the highest near the eddy's center (up to ~40 µmol L−1). δ15N-N2 also varied with biogenic N2 production, following kinetic isotopic fractionation during NO2− reduction to N2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ε for NO3− reduction (up to ~30‰ in the presence of NO2−). However, the overall ε for N-loss was calculated to be only ~13–14‰ (as compared to canonical values of ~20–30‰) assuming a closed system and only slightly higher assuming an open system (16–19‰). Our results were similar whether calculated from the disappearance of DIN (NO3− + NO2−) or from the appearance of N2 and changes in isotopic composition. Further, we calculated the separate ε values for NO3− reduction to NO2− and NO2− reduction to N2 of ~16–21‰ and ~12‰, respectively, when the effect of NO2− oxidation could be removed. These results, together with the relationship between N and O of NO3− isotopes and the difference in δ15N between NO3− and NO2−, confirm a role for NO2− oxidation in increasing the apparent ε associated with NO3− reduction. The lower ε for N-loss calculated in this study could help reconcile the current imbalance in the global N budget if representative of global OMZ N-loss. en_US
dc.description.embargo 2015-12-06 en_US
dc.description.sponsorship This work was supported by the Deutsche Forschungsgemeinschaft- project SFB-754 (www.sfb754.de), SOPRAN II (grant FKZ 03F0611A; www.sopran.pangaea.de), NSF grants OCE 0851092 and OCE 1154741 to M.A.A., and a NSERC Postdoctoral Fellowship to A.B. en_US
dc.format.mimetype application/pdf
dc.identifier.citation Global Biogeochemical Cycles 29 (2015): 793-811 en_US
dc.identifier.doi 10.1002/2014GB005001
dc.identifier.uri https://hdl.handle.net/1912/7464
dc.language.iso en_US en_US
dc.publisher John Wiley & Sons en_US
dc.relation.uri https://doi.org/10.1002/2014GB005001
dc.subject Mesoscale eddy en_US
dc.subject Isotope effects en_US
dc.subject N-loss en_US
dc.title N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment en_US
dc.type Article en_US
dspace.entity.type Publication
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