Close coupling of N‐cycling processes expressed in stable isotope data at the redoxcline of the Baltic Sea

Frey, Claudia; Dippner, Joachim W.; Voß, Maren

doi:10.1002/2013gb004642

Cited by 13 publications

(15 citation statements)

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“…In July 2008, frozen and acidified samples were also similar, though not necessarily measured at the same depths (Figure f). These values are quite similar to those seen in the oxycline and suboxic zone of the Baltic Sea (Frey et al, ).…”

Section: Resultssupporting

confidence: 89%

“…However, the calculated δ 15 N‐N 2 of the in situ biological N 2 in the oxycline in March 2005 ranged from +7‰ to +38‰. Even though these isotope effects are reduced in systems like the Black and Baltic Seas, where reactants are completely consumed in the suboxic zone (Frey et al, ; Konovalov et al, ), in all normal cases, the reactant, NO x − , should become more enriched and the product, N 2 , more depleted.…”

Section: Discussionmentioning

confidence: 99%

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Detection of Transient Denitrification During a High Organic Matter Event in the Black Sea

Fuchsman

Paul

Staley

et al. 2019

Global Biogeochemical Cycles

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N2 production by denitrification can occur in anoxic water or potentially inside organic particles. Here we compare data from the Black Sea, a permanently anoxic basin, during two organic matter regimes: suspended particulate organic matter concentrations were high in the oxycline after the spring bloom in March 2005 compared to lower organic matter concentrations in June 2005, May and October 2007, July 2008, and May 2001. For all cruises, N2 gas had a maximum in the suboxic zone (O2 < 10 μmol/L). During the high organic matter event (March 2005), an additional shallower N2 gas and δ15N‐N2 maxima occurred above the suboxic zone in the oxycline where oxygen concentrations were 30–50 μmol/L. Examination of 16S rRNA indicated that anammox bacteria were not present in the oxycline. The δ15N of biologically produced N2 in the oxycline in March 2005 was significantly enriched (+7‰ to +38‰), not depleted, as would be expected from water column fractionation. A simple diffusion calculation indicated that ammonium produced from remineralization inside particles could be oxidized to nitrate and then completely consumed by denitrification inside the particle. In this calculation, half of denitrified N atoms originated from organic N [δ15N = 11‰] and half of N atoms originated from ambient nitrate [δ15N = 5‰–7‰], producing enriched δ15N‐N2 values. We suggest that denitrifiers were active in microzones inside particulates in hypoxic waters above the suboxic zone of the Black Sea. Denitrification in particles may also explain previous data from the oxycline above ocean oxygen deficient zones.

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Section: Resultssupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Detection of Transient Denitrification During a High Organic Matter Event in the Black Sea

Fuchsman

Paul

Staley

et al. 2019

Global Biogeochemical Cycles

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“…We still observed lower than expected 15 ε NO3‐ red , despite only using data points deeper than 100 m (the peak in chlorophyll α being at ~50 m depth) to minimize NO 3 − assimilation effects (Table ). One explanation could be partial suppression of 15 ε NO3‐ red at low [NO 3 − ] within the OMZ as the system approached nearly complete substrate consumption (NO 3 − and NO 2 − ), as suggested by previous studies [ Granger et al, ; Kritee et al, ; Frey et al, ]. However, the onset of this asymptotic behavior between δ 15 N‐NO 3 − (or DIN) and ln[f] was observed in this study at lower substrate concentrations ([NO 3 − ] or ([NO 3 − ] + [NO 2 − ]) < ~13 µmol L −1 ) as compared to the threshold of ~35μmol L −1 reported by Kritee et al [] for laboratory experiments.…”

Section: Resultssupporting

confidence: 61%

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

Bourbonnais

Altabet

Charoenpong

et al. 2015

Global Biogeochemical Cycles

105

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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 (NO 3 À ), nitrite (NO 2 À ), and biogenic N 2 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 NO 3 À was nearly exhausted, we measured the highest δ 15 N values for both NO 3 À and NO 2 À (up to~70‰ and 50‰) ever reported for an OMZ.Correspondingly, N deficit and biogenic N 2 -N concentrations were also the highest near the eddy's center (up tõ 40 μmol L À1 ). δ 15 N-N 2 also varied with biogenic N 2 production, following kinetic isotopic fractionation during NO 2 À reduction to N 2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ε for NO 3 À reduction (up to~30‰ in the presence of NO 2 À ).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 (NO 3 À + NO 2 À ) or from the appearance of N 2 and changes in isotopic composition. Further, we calculated the separate ε values for NO 3 À reduction to NO 2 À and NO 2 À reduction to N 2 of~16-21‰ and~12‰, respectively, when the effect of NO 2 À oxidation could be removed. These results, together with the relationship between N and O of NO 3 À isotopes and the difference in δ 15 N between NO 3 À and NO 2 À , confirm a role for NO 2 À oxidation in increasing the apparent ε associated with NO 3 À 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.

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“…12,20 A reduced ε in the presence of oxygen due to a reduced CSNR rate was previously reported, 20 but oxygen does not seem to be the reason for the low ε apparent of 4.7‰ found in the Baltic Sea redoxcline. 26 The only significant impact on 15 ε occurred under unstirred conditions, as previously described for a Marinobacter culture. 20 In that study, diffusion limitation due to a diffusive boundary layer around each cell was excluded as an explanation because the bacterial cells were too small and the substrate concentrations too high to result in a concentration gradient, which may also have been the case in our study.…”

Section: Oxygen Sensitivity Of Chemolithoautotrophicmentioning

confidence: 61%

N and O Isotope Fractionation in Nitrate during Chemolithoautotrophic Denitrification by Sulfurimonas gotlandica

Frey

Hietanen

Jürgens

et al. 2014

Environ. Sci. Technol.

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Chemolithoautotrophic denitrification is an important mechanism of nitrogen loss in the water column of euxinic basins, but its isotope fractionation factor is not known. Sulfurimonas gotlandica GD1(T), a recently isolated bacterial key player in Baltic Sea pelagic redoxcline processes, was used to determine the isotope fractionation of nitrogen and oxygen in nitrate during denitrification. Under anoxic conditions, nitrate reduction was accompanied by nitrogen and oxygen isotope fractionation of 23.8 ± 2.5‰ and 11.7 ± 1.1‰, respectively. The isotope effect for nitrogen was in the range determined for heterotrophic denitrification, with only the absence of stirring resulting in a significant decrease of the fractionation factor. The relative increase in δ(18)ONO3 to δ(15)NNO3 did not follow the 1:1 relationship characteristic of heterotrophic, marine denitrification. Instead, δ(18)ONO3 increased slower than δ(15)NNO3, with a conserved ratio of 0.5:1. This result suggests that the periplasmic nitrate reductase (Nap) of S. gotlandica strain GD1(T) fractionates the N and O in nitrate differently than the membrane-bound nitrate reductase (Nar), which is generally prevalent among heterotrophic denitrifiers and is considered as the dominant driver for the observed isotope fractionation. Hence in the Baltic Sea redoxcline, other, as yet-unidentified factors likely explain the low apparent fractionation.

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Close coupling of N‐cycling processes expressed in stable isotope data at the redoxcline of the Baltic Sea

Cited by 13 publications

References 100 publications

Detection of Transient Denitrification During a High Organic Matter Event in the Black Sea

Detection of Transient Denitrification During a High Organic Matter Event in the Black Sea

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

N and O Isotope Fractionation in Nitrate during Chemolithoautotrophic Denitrification by Sulfurimonas gotlandica

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