Simulating the global distribution of nitrogen isotopes in the ocean

Somes, Christopher J.; Schmittner, Andreas; Galbraith, Eric D.; Lehmann, Moritz F.; Altabet, Mark A.; Montoya, Joseph P.; Letelier, Ricardo M.; Mix, Alan C; Bourbonnais, Annie; Eby, Michael

doi:10.1029/2009gb003767

Cited by 211 publications

(225 citation statements)

References 110 publications

(149 reference statements)

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“…However, apart from one Paleoproterozoic δ 15 N dataset that has been explained by that mechanism (Papineau et al, 2009), there is so far no evidence of partial NH 4 + assimilation and hence for a large deep marine NH 4 + reservoir. This observation may suggest that NH 4 + concentrations were similar to or lower than modern marine NO 3 -levels (~30μM), which are assimilated quantitatively in most environments except at high latitudes (Altabet and Francois, 1994;Somes et al, 2010). The Black Sea with its 100 μM of NH 4 + is an imperfect analogue, because upwelling is weak and so this NH 4 + is not readily bioavailable to organisms at the surface (Özsoy and Ünlüata, 1997).…”

Section: Was the Precambrian Ocean Rich In Nh 4 + ?mentioning

confidence: 99%

“…Fractionations associated with NO 3 -assimilation are often not expressed because assimilation typically goes to completion (Altabet and Francois, 1994;Thunell et al, 2004), except in modern Arctic settings (Somes et al, 2010). Under oxic conditions, marine sediments therefore approach the isotopic composition of NO 3 -in the overlying water column (Altabet and Francois, 1994;Thunell et al, 2004).…”

Section: A Primer On Nitrogen Isotopes In Geological Samplesmentioning

confidence: 99%

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The evolution of Earth's biogeochemical nitrogen cycle

Stüeken

Kipp

Koehler

et al. 2016

Earth-Science Reviews

328

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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Section: Was the Precambrian Ocean Rich In Nh 4 + ?mentioning

confidence: 99%

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

328

287

View full text Add to dashboard Cite

show abstract

“…Given the logistical challenges of generating extensive spatial and temporal coverage of observational data, the development of robust isoscapes would be greatly improved with a more mechanistic understanding of what establishes and maintains isoscape structure. This will likely require developing process-based, coupled biogeochemical-physical ocean models to reconstruct baseline marine isoscapes (Schmittner et al 2008;Somes et al 2010). Enhanced knowledge of isotopic routing and fractionation factors, particularly of individual compound classes, is also necessary to fully realize the potential of ocean ecogeochemistry.…”

Section: Applicationsmentioning

confidence: 99%

A review of ecogeochemistry approaches to estimating movements of marine animals

McMahon

Hamady

Thorrold

2013

Limnology & Oceanography

345

313

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Ecogeochemistry-the application of geochemical techniques to fundamental questions in population and community ecology-has been used in animal migration studies in terrestrial environments for several decades; however, the approach has received far less attention in marine systems. This review includes comprehensive meta-analyses of organic zooplankton d 13 C and d 15 N values at the base of the food web, dissolved inorganic carbon d 13 C values, and seawater d 18 O values to create, for the first time, robust isoscapes for the Atlantic Ocean. These isoscapes present far greater geographic variability in multiple geochemical tracers than was previously thought, thus forming the foundation for reconstructions of habitat use and migration patterns of marine organisms. We review several additional tracers, including trace-element-to-calcium ratios and heavy element stable isotopes, to examine anadromous migrations. We highlight the value of the ecogeochemistry approach by examining case studies on three components of connectivity: dispersal and natal homing, functional connectivity, and migratory connectivity. We also discuss recent advances in compound-specific stable carbon and nitrogen isotope analyses for tracking animal movement. A better understanding of isotopic routing and fractionation factors, particularly of individual compound classes, is necessary to realize the full potential of ecogeochemistry.

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“…The main source of δ 15 N into the pre-industrial ocean is from diazotrophs that fix 15 N-depleted atmospheric N 2 into their biomass (δ 15 N Diaz = −2-0 ‰) relative to the deep ocean δ 15 NO − 3 = 5 ‰ (Sigman et al, 2000;Somes et al, 2010b), with minor contributions from atmospheric deposition (δ 15 N dep = ∼ −4 ‰) and rivers (δ 15 N riv = ∼ 1-4 ‰) (Brandes and Devol, 2002). Denitrifying bacteria preferentially consume 15 N-depleted nitrate, the lighter and more reactive isotope, during WCD (ε WCD = 20-30 ‰), leaving the oceanic nitrate pool 15 N-enriched (Cline and Kaplan, 1975;Brandes et al, 1998;Voss et al, 2001).…”

Section: J Somes Et Al: Isotopic Constraints On the Pre-industrimentioning

confidence: 99%

Isotopic constraints on the pre-industrial oceanic nitrogen budget

2013

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The size of the bioavailable (i.e., "fixed") nitrogen inventory in the ocean influences global marine productivity and the biological carbon pump. Despite its importance, the pre-industrial rates for the major source and sink terms of the oceanic fixed nitrogen budget, N₂ fixation and denitrification, respectively, are not well known. These processes leave distinguishable imprints on the ratio of stable nitrogen isotopes, δ¹⁵N, which can therefore help to infer their patterns and rates. Here we use δ¹⁵N observations from the water column and a new database of seafloor measurements to constrain rates of N₂ fixation and denitrification predicted by a global three-dimensional Model of Ocean Biogeochemistry and Isotopes (MOBI). Sensitivity experiments were performed to quantify uncertainties associated with the isotope effect of denitrification in the water column and sediments. They show that the level of nitrate utilization in suboxic zones, that is the balance between nitrate consumption by denitrification and nitrate replenishment by circulation and mixing (dilution effect), significantly affects the isotope effect of water column denitrification and thus global mean δ¹⁵NO₃^–. Experiments with lower levels of nitrate utilization within the suboxic zone (i.e., higher residual water column nitrate concentrations, ranging from 20 to 32 μM) require higher ratios of benthic to water column denitrification, BD : WCD = 0.75–1.4, to satisfy the global mean NO₃^– and δ¹⁵NO₃^– constraints in the modern ocean. This suggests that nitrate utilization in suboxic zones plays an important role in global nitrogen isotope cycling. Increasing the net fractionation factor ϵ_BD for benthic denitrification (ϵ_BD = 0–4‰) requires even higher ratios, BD : WCD = 1.4–3.5. The model experiments that best reproduce observed seafloor δ¹⁵N support the middle to high-end estimates for the net fractionation factor of benthic denitrification (ϵ_BD = 2–4‰). Assuming a balanced fixed nitrogen budget, we estimate that pre-industrial rates of N₂ fixation, water column denitrification, and benthic denitrification were between 195–350 (225), 65–80 (76), and 130–270 (149) Tg N yr⁻¹, respectively, with our best model estimate (ϵ_BD = 2‰) in parentheses. Although uncertainties still exist, these results suggest that marine N₂ fixation is occurring at much greater rates than previously estimated and the residence time for oceanic fixed nitrogen is between ~ 1500 and 3000 yr

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Simulating the global distribution of nitrogen isotopes in the ocean

Cited by 211 publications

References 110 publications

The evolution of Earth's biogeochemical nitrogen cycle

The evolution of Earth's biogeochemical nitrogen cycle

A review of ecogeochemistry approaches to estimating movements of marine animals

Isotopic constraints on the pre-industrial oceanic nitrogen budget

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