Reduced isotope fractionation by denitrification under conditions relevant to the ocean

Kritee, K.; Sigman, Daniel M.; Granger, Julie; Ward, Bess B.; Jayakumar, Amal; Deutsch, Curtis

doi:10.1016/j.gca.2012.05.020

Cited by 140 publications

(173 citation statements)

References 88 publications

(127 reference statements)

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“…This possibility will be explored further in the next section. Unlikely explanations for our relatively low ε values for N-loss include the effects of decreasing NO − 3 concentration (Kritee et al, 2012) and contributions from organic N via anammox to biogenic N 2 . Lack of curvature in the Rayleigh plots demonstrates a lack of dependence of substrate concentration (Fig.…”

Section: Isotope Effects For N-lossmentioning

confidence: 58%

Nitrogen cycling in shallow low-oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

Bourbonnais

Larkum

et al. 2016

Biogeosciences

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Abstract. O 2 deficient zones (ODZs) of the world's oceans are important locations for microbial dissimilatory nitrate (NO − 3 ) reduction and subsequent loss of combined nitrogen (N) to biogenic N 2 gas. ODZs are generally coupled to regions of high productivity leading to high rates of N-loss as found in the coastal upwelling region off Peru. Stable N and O isotope ratios can be used as natural tracers of ODZ Ncycling because of distinct kinetic isotope effects associated with microbially mediated N-cycle transformations. Here we present NO − 3 and nitrite (NO − 2 ) stable isotope data from the nearshore upwelling region off Callao, Peru. Subsurface oxygen was generally depleted below about 30 m depth with concentrations less than 10 µM, while NO − 2 concentrations were high, ranging from 6 to 10 µM, and NO − 3 was in places strongly depleted to near 0 µM. We observed for the first time a positive linear relationship between NO − 2 δ 15 N and δ 18 O at our coastal stations, analogous to that of NO − 3 N and O isotopes during NO − 3 uptake and dissimilatory reduction. This relationship is likely the result of rapid NO − 2 turnover due to higher organic matter flux in these coastal upwelling waters. No such relationship was observed at offshore stations where slower turnover of NO − 2 facilitates dominance of isotope exchange with water. We also evaluate the overall isotope fractionation effect for N-loss in this system using several approaches that vary in their underlying assumptions. While there are differences in apparent fractionation factor (ε) for N-loss as calculated from the δ 15 N of NO − 3 , dissolved inorganic N, or biogenic N 2 , values for ε are generally much lower than previously reported, reaching as low as 6.5 ‰. A possible explanation is the influence of sedimentary N-loss at our inshore stations which incurs highly suppressed isotope fractionation.

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Section: Isotope Effects For N-lossmentioning

confidence: 58%

Nitrogen cycling in shallow low-oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

Bourbonnais

Larkum

et al. 2016

Biogeosciences

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“…More recent work suggests that sedimentary denitrification imparts a net fractionation of -3‰ (Kessler et al, 2014;Rooze and Meile, 2016), i.e. producing N 2 gas with δ 15 N N2 = +2‰, while water-column denitrification only has a net fractionation of -12.5‰ (δ 15 N N2 = -7.5‰) (Kritee et al, 2012;Rooze and Meile, 2016). In that case, the mass balance of the two processes would be 68% to 32%.…”

Section: A Primer On Nitrogen Isotopes In Geological Samplesmentioning

confidence: 99%

The evolution of Earth's biogeochemical nitrogen cycle

Stüeken

Kipp

Koehler

et al. 2016

Earth-Science Reviews

329

287

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Nitrogen is an essential nutrient for all life on Earth and it acts as a major control on biological productivity in the modern ocean. Accurate reconstructions of the evolution of life over the course of the last four billion years therefore demand a better understanding of nitrogen bioavailability and speciation through time. The biogeochemical nitrogen cycle has evidently been closely tied to the redox state of the ocean and atmosphere. Multiple lines of evidence indicate that the Earth"s surface has passed in a non-linear fashion from an anoxic state in the Hadean to an oxic state in the later Phanerozoic. It is therefore likely that the nitrogen cycle has changed markedly over time, with potentially severe implications for the productivity and evolution of the biosphere. Here we compile nitrogen isotope data from the literature and review our current understanding of the evolution of the nitrogen cycle, with particular emphasis on the Precambrian. Combined with recent work on redox conditions, trace metal availability, sulfur and iron cycling on the early Earth, we then use the nitrogen isotope record as a platform to test existing and new hypotheses about biogeochemical pathways that may have controlled nitrogen availability through time. Among other things, we conclude that (a) abiotic nitrogen sources were likely insufficient to sustain a large biosphere, thus favoring an early origin of biological N 2 fixation, (b) evidence of nitrate in the Neoarchean and Paleoproterozoic confirm current views of increasing surface oxygen levels at those times, (c) abundant ferrous iron and sulfide in the midPrecambrian ocean may have affected the speciation and size of the fixed nitrogen reservoir, and (d) nitrate availability alone was not a major driver of eukaryotic evolution.

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“…When NO 2 À oxidation and NO 3 À reduction occur at the organismal scale, the enzymatic isotope effects of the two processes can be underexpressed due to substantial consumption of the substrate within the cells of nitrifiers and denitrifiers [e.g., Kritee et al, 2012]. Thus, compensating NO 3 À reduction and NO 2 À oxidation by a consortium of nitrate reducers and nitrite oxidizers in an ocean water parcel are unlikely to approximate the equilibrium N isotope effect between NO 3 À and NO 2 À .…”

Section: /2015gb005350mentioning

confidence: 99%

Enzyme‐level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

Kemeny

Weigand

Zhang

et al. 2016

Global Biogeochemical Cycles

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Reduced isotope fractionation by denitrification under conditions relevant to the ocean

Cited by 140 publications

References 88 publications

Nitrogen cycling in shallow low-oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

Nitrogen cycling in shallow low-oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

The evolution of Earth's biogeochemical nitrogen cycle

Enzyme‐level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

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