Oceanic nitrogen cycling and N<sub>2</sub>O flux perturbations in the Anthropocene

Landolfi, Angela; Somes, Christopher J.; Koeve, Wolfgang; Zamora, Lauren; Oschlies, Andreas

doi:10.1002/2017gb005633

Cited by 57 publications

(87 citation statements)

References 101 publications

(174 reference statements)

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“…The increase in NO 2 − reduction, however, leads to an increase in global water column N loss from an average of 61 Tg N/year in the base model to 72 and 89 Tg N/year for the K m NXR = 5 μM and K m NXR = 20 μM cases, respectively. This increase in water column N loss is at the higher end of many recent estimates (Table 1; Landolfi et al, 2017), though still within the range of uncertainty. Higher rates of N loss with reduced NO 2 − oxidation are consistent with the idea that "recycling" of NO 3 − via NO 2 − oxidation prevents N from being lost from the DIN pool via NO 2 − reduction (Bristow et al, 2017;Casciotti et al, 2013;Penn et al, 2016).…”

Section: Sensitivity Of Nitrite Oxidation To Model Parameterssupporting

confidence: 61%

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Martin

Primeau

Casciotti

2019

Global Biogeochemical Cycles

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We present results from a global inverse marine nitrogen (N) cycle model that include nitrate (NO3−) and nitrite (NO2−) concentrations and their N isotopic compositions as constraints on N cycle process rates in marine oxygen deficient zones (ODZs). NO2− is an important intermediate in the N cycle, particularly in ODZs where it is a substrate in the N loss processes, denitrification, and anammox. Similar to earlier work, our model yields a total water column N loss rate of 61 ± 10 Tg N/year. However, by including NO2− and its N isotopic composition, we are able to assess the relative contributions of denitrification and anammox to N loss and examine some of the potential drivers of that balance. We find that anammox contributes 60% of global water column N loss, dominating N loss along the edges of ODZs, while denitrification is more important in the anoxic ODZ cores. The decoupling of anammox and denitrification is supported by NO2− oxidation, which co‐occurs with NO3− reduction and anammox in ODZs. High rates of NO2− oxidation (up to 400 nM/day), which are tightly coupled to heterotrophic NO3− reduction, are required to match NO3− and NO2− concentration and isotope observations in marine ODZs. Lowering the rate of NO2− oxidation in ODZs by adjusting O2‐sensitive parameters results in higher rates of water column N loss, highlighting the role of NO2− oxidation in maintaining the marine fixed N inventory.

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Section: Sensitivity Of Nitrite Oxidation To Model Parameterssupporting

confidence: 61%

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Martin

Primeau

Casciotti

2019

Global Biogeochemical Cycles

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“…The Intergovernmental Panel on Climate Change reports that the ocean contributes 3.8 Tg‐N/year (1 Tg = 10 12 g), ~21% of the total N 2 O emissions (Ciais et al, ). However, incomplete understanding of marine N 2 O production pathways and their sensitivities to environmental factors resulted in large uncertainties of current N 2 O emission estimates (1.8–9.4 Tg‐N/year) and limited our ability to predict future N 2 O emission under the changing ocean and climate (Battaglia & Joos, ; Landolfi et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…However, incomplete understanding of marine N 2 O production pathways and their sensitivities to environmental factors resulted in large uncertainties of current N 2 O emission estimates (1. 8-9.4 Tg-N/year) and limited our ability to predict future N 2 O emission under the changing ocean and climate (Battaglia & Joos, 2018;Landolfi et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Global Nitrous Oxide Production Determined by Oxygen Sensitivity of Nitrification and Denitrification

Buitenhuis

Suntharalingam

et al. 2018

Global Biogeochemical Cycles

127

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The ocean is estimated to contribute up to ~20% of global fluxes of atmospheric nitrous oxide (N2O), an important greenhouse gas and ozone depletion agent. Marine oxygen minimum zones contribute disproportionately to this flux. To further understand the partition of nitrification and denitrification and their environmental controls on marine N2O fluxes, we report new relationships between oxygen concentration and rates of N2O production from nitrification and denitrification directly measured with 15N tracers in the Eastern Tropical Pacific. Highest N2O production rates occurred near the oxic‐anoxic interface, where there is strong potential for N2O efflux to the atmosphere. The dominant N2O source in oxygen minimum zones was nitrate reduction, the rates of which were 1 to 2 orders of magnitude higher than those of ammonium oxidation. The presence of oxygen significantly inhibited the production of N2O from both nitrification and denitrification. These experimental data provide new constraints to a multicomponent global ocean biogeochemical model, which yielded annual oceanic N2O efflux of 1.7–4.4 Tg‐N (median 2.8 Tg‐N, 1 Tg = 1012 g), with denitrification contributing 20% to the oceanic flux. Thus, denitrification should be viewed as a net N2O production pathway in the marine environment.

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“…We applied the University of Victoria (UVic) Earth System Model (ESM) version 2.9 (Weaver et al, 2001), which has been used in several studies to investigate ocean oxygen dynamics (Schmittner et al, 85 2007;Oschlies et al, 2008;Getzlaff et al, 2016;Keller et al, 2016;Landolfi et al, 2017). The UVic model consists of a terrestrial model based on TRIFFID and MOSES (Meissner et al, 2003), an atmospheric energy-moisture-balance model (Fanning and Weaver, 1996), a sea-ice model (Bitz and Lipscomb, 1999) and the general ocean circulation model MOM2 (Pacanowski, 1996).…”

Section: Modelmentioning

confidence: 99%

Ocean Phosphorus Inventory and Ocean Deoxygenation: Large Uncertainties in Future Projections on Millennial Timescales

Kemena

Oschlies

Koeve

et al. 2018

Preprint

Self Cite

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Previous studies have suggested that weathering and benthic phosphorus (P) fluxes, triggered by 10 climate warming, can increase the oceanic P inventory on millennial time scales, promoting ocean productivity and deoxygenation. In this study, we assessed the major uncertainties in projected P inventories and their imprint on ocean deoxygenation using an Earth system model of intermediate complexity for a business-as-usual carbon dioxide (CO 2 ) emission scenario until year 2300 and subsequent linear decline to zero emissions until year 3000. 15Model results suggest a large spread in the simulated oceanic P inventory due to uncertainties in (1) assumptions for weathering parameters, (2) the representation of bathymetry on slopes and shelves in the model bathymetry, (3) the parametrization of benthic P fluxes and (4) the representation of sediment P inventories. Our best estimate for changes in the global ocean P inventory by the year 5000 caused by global warming amounts to +30% compared to pre-industrial levels. Weathering, benthic 20 and anthropogenic fluxes of P contributed +25%, +3% and +2% respectively. The total range of oceanic P inventory changes across all model simulations varied between +2% and +60%. Suboxic volumes were up to 5 times larger than in a model simulation with a constant oceanic P inventory.Considerably large amounts of the additional P left the ocean surface unused by phytoplankton via physical transport processes as preformed P. Nitrogen fixation was not able to adjust the oceanic 25 nitrogen inventory to the increasing P levels or to compensate for the nitrogen loss due to increased denitrification. This is in contrast to palaeo reconstructions of large-scale deoxygenation events.We suggest that uncertainties in P weathering, nitrogen fixation and benthic P feedbacks need to be reduced to achieve more reliable projections of oceanic deoxygenation on millennial timescales.

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Oceanic nitrogen cycling and N₂O flux perturbations in the Anthropocene

Cited by 57 publications

References 101 publications

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Global Nitrous Oxide Production Determined by Oxygen Sensitivity of Nitrification and Denitrification

Ocean Phosphorus Inventory and Ocean Deoxygenation: Large Uncertainties in Future Projections on Millennial Timescales

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Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene

Cited by 57 publications

References 101 publications

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3‐D Inverse Model

Global Nitrous Oxide Production Determined by Oxygen Sensitivity of Nitrification and Denitrification

Ocean Phosphorus Inventory and Ocean Deoxygenation: Large Uncertainties in Future Projections on Millennial Timescales

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Oceanic nitrogen cycling and N₂O flux perturbations in the Anthropocene