Marine denitrification rates determined from a global 3-D inverse model

DeVries, Tim; Deutsch, Curtis; Rafter, Patrick A.; Primeau, François

doi:10.5194/bg-10-2481-2013

Cited by 136 publications

(138 citation statements)

References 48 publications

Supporting

Mentioning

107

Contrasting

Order By: Relevance

“…However, models including this process suggest that BD does not contribute to fostering N 2 fixation in the oligotrophic North Atlantic [Weber and Deutsch, 2012]. This is consistent with observational estimates of relatively low rates of North Atlantic BD [DeVries et al, 2013] and resulting P* supply [Palter et al, 2011].…”

Section: Resultssupporting

confidence: 67%

A new perspective on environmental controls of marine nitrogen fixation

Landolfi

Koeve

Dietze

et al. 2015

Geophysical Research Letters

View full text Add to dashboard Cite

Growing slowly, marine N2 fixers are generally expected to be competitive only where nitrogen (N) supply is low relative to that of phosphorus (P) with respect to the cellular N:P ratio (R) of nonfixing phytoplankton. This is at odds with observed high N2 fixation rates in the oligotrophic North Atlantic where the ratio of nutrients supplied to the surface is elevated in N relative to the average R (16:1). In this study, we investigate several mechanisms to solve this puzzle: iron limitation, phosphorus enhancement by preferential remineralization or stoichiometric diversity of phytoplankton, and dissolved organic phosphorus (DOP) utilization. Combining resource competition theory and a global coupled ecosystem‐circulation model, we find that the additional N and energy investments required for exoenzymatic breakdown of DOP give N2 fixers a competitive advantage in oligotrophic P‐starved regions. Accounting for this mechanism expands the ecological niche of N2 fixers also to regions where the nutrient supply is high in N relative to R, yielding, in our model, a pattern consistent with the observed high N2 fixation rates in the oligotrophic North Atlantic.

show abstract

Section: Resultssupporting

confidence: 67%

A new perspective on environmental controls of marine nitrogen fixation

Landolfi

Koeve

Dietze

et al. 2015

Geophysical Research Letters

View full text Add to dashboard Cite

show abstract

“…MOBI experiments #4 and #5 predict BD rates on the continental shelves (60 and 108 Tg N yr −1 , respectively) that are on the low-end of most recent estimates (80-125 Tg N yr −1 ) (Bianchi et al, 2012;Bohlen et al, 2012;DeVries et al, 2013) and much lower than another estimate of 250 Tg N yr −1 (Seitzinger et al, 2006). If much more BD is occurring on the continental shelves than predicted by MOBI, this can impact the isotope effect of BD because δ 15 NO − 3 of bottom water on the shelves is on average ∼ 1.5 ‰ higher compared to the deep ocean in the model due to its close proximity to surface NO − 3 utilization.…”

Section: Discussionmentioning

confidence: 98%

“…These values were chosen to produce WCD rates that lie within the range of modern estimates between 50 and 150 Tg N yr −1 . Note that recent studies report a new low-end estimate for water column denitrification rate (∼ 50 Tg N yr −1 ) (Eugster and Gruber, 2013;DeVries et al, 2013), which is not explicitly tested in our model experiments that cover the range 75-140 Tg N yr −1 .…”

Section: Water Column Denitrification Experimentsmentioning

confidence: 93%

“…In the water column, studies suggest global rates between 50 and 150 Tg N yr −1 and in the sediments generally between 100 and 300 Tg N yr −1 (Middelburg et al, 1996;Galloway et al, 2004;Codispoti, 2007;Bohlen et al, 2012;DeVries et al, 2013;Eugster and Gruber, 2012). Since the high-end estimates for denitrification are substantially larger than the high-end estimates for N 2 fixation, it has led to the debate whether the ocean could be rapidly losing as much as 400 Tg N yr −1 (Codispoti et al, 2001;Brandes and Devol, 2002;Seitzinger et al, 2006;Codispoti, 2007), about 0.07 % of the total nitrate inventory per year, or whether the nitrogen budget is more balanced (Gruber and Sarmiento, 1997;Altabet, 2007;Bianchi et al, 2012).…”

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

confidence: 99%

See 1 more Smart Citation

Isotopic constraints on the pre-industrial oceanic nitrogen budget

2013

View full text Add to dashboard Cite

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

show abstract

“…Oceanic waters characterized by oxygen-deficient conditions (<4.5 μmol·L −1 O 2 ) account for <0.1% of total ocean volume but for >30% of fixed nitrogen (N) loss (3)(4)(5)(6) due to the onset of anaerobic processes, including denitrification and anammox (7)(8)(9)(10). Both field and modeling observations point to the expansion of low oxygen regions as a result of global warming (11).…”

mentioning

confidence: 99%

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Bristow

Dalsgaard

Tiano

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

202

209

View full text Add to dashboard Cite

A major percentage of fixed nitrogen (N) loss in the oceans occurs within nitrite-rich oxygen minimum zones (OMZs) via denitrification and anammox. It remains unclear to what extent ammonium and nitrite oxidation co-occur, either supplying or competing for substrates involved in nitrogen loss in the OMZ core. Assessment of the oxygen (O 2 ) sensitivity of these processes down to the O 2 concentrations present in the OMZ core (<10 nmol·L −1 ) is therefore essential for understanding and modeling nitrogen loss in OMZs. We determined rates of ammonium and nitrite oxidation in the seasonal OMZ off Concepcion, Chile at manipulated O 2 levels between 5 nmol·L −1 and 20 μmol·L −1 . Rates of both processes were detectable in the low nanomolar range (5-33 nmol·L −1 O 2 ), but demonstrated a strong dependence on O 2 concentrations with apparent half-saturation constants (K m s) of 333 ± 130 nmol·L −1 O 2 for ammonium oxidation and 778 ± 168 nmol·L −1 O 2 for nitrite oxidation assuming one-component Michaelis-Menten kinetics. Nitrite oxidation rates, however, were better described with a two-component Michaelis-Menten model, indicating a high-affinity component with a K m of just a few nanomolar. As the communities of ammonium and nitrite oxidizers were similar to other OMZs, these kinetics should apply across OMZ systems. The high O 2 affinities imply that ammonium and nitrite oxidation can occur within the OMZ core whenever O 2 is supplied, for example, by episodic intrusions. These processes therefore compete with anammox and denitrification for ammonium and nitrite, thereby exerting an important control over nitrogen loss.is a key factor regulating biogeochemical cycling in the marine environment (1). Although the vast majority of the ocean remains well oxygenated, subsurface regions of extreme oxygen depletion can persist along eastern boundaries of the world's ocean basins. These regions are known as oxygen minimum zones (OMZs) and are located within the eastern tropical North and South Pacific, the Arabian Sea, and off the coast of Namibia, where oxygen depletion results from poor ventilation and a high export of organic matter from productive surface waters, generating high rates of subsurface oxygen consumption (2, 3).Oceanic waters characterized by oxygen-deficient conditions (<4.5 μmol·L −1 O 2 ) account for <0.1% of total ocean volume but for >30% of fixed nitrogen (N) loss (3-6) due to the onset of anaerobic processes, including denitrification and anammox (7-10). Both field and modeling observations point to the expansion of low oxygen regions as a result of global warming (11). Thus, to evaluate the biogeochemical impact of these regions, it is imperative to understand fully how oxygen controls the cycling of substrates involved in nitrogen loss pathways.Recent studies have quantified the oxygen sensitivity of anaerobic OMZ nitrogen transformations, finding that denitrification has relatively low oxygen tolerance with a half-inhibition concentration (IC 50 ) of 0.3 μmol·L −1 , compared with higher values for...

show abstract

Marine denitrification rates determined from a global 3-D inverse model

Cited by 136 publications

References 48 publications

A new perspective on environmental controls of marine nitrogen fixation

A new perspective on environmental controls of marine nitrogen fixation

Isotopic constraints on the pre-industrial oceanic nitrogen budget

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Contact Info

Product

Resources

About