Nitrous oxide in the North Atlantic Ocean

Walter, Sylvia; Bange, Hermann W.; Breitenbach, U.; Wallace, Douglas W.R.

doi:10.5194/bg-3-607-2006

Cited by 83 publications

(108 citation statements)

References 51 publications

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“…The N 2 O amount in the sample can be calculated from the peak area with a precision of 2 % (based on analysis of replicates) and the sample volume, which is determined by sample weight, water temperature and salinity, with a precision of 0.02 %. The overall precision of 2 % is comparable to the 1.8 % concentration uncertainty achieved for GC-ECD measurements by Walter et al (2006) and 2.6 % for GC-MS measurements by McIlvin and Casciotti (2010). …”

Section: Gc-ms Measurements Of Discrete Samplessupporting

confidence: 56%

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Grefe

Kaiser

2014

Ocean Sci.

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Abstract. Dissolved nitrous oxide (N 2 O) concentrations are usually determined by gas chromatography (GC). Here we present laboratory tests and initial field measurements using a novel setup comprising a commercially available laser-based analyser for N 2 O, carbon monoxide and water vapour coupled to a glass-bed equilibrator. This approach is less labourintensive and provides higher temporal and spatial resolution than the conventional GC technique. The standard deviation of continuous equilibrator or atmospheric air measurements was 0.2 nmol mol −1 (averaged over 5 min). The shortterm repeatability for reference gas measurements within 1 h of each other was 0.2 nmol mol −1 or better. Another indicator of the long-term stability of the analyser is the standard deviation of the calibrated N 2 O mole fraction in marine air, which was between 0.5 and 0.7 nmol mol −1 . The equilibrator measurements were compared with purge-and-trap gas chromatography-mass spectrometry (GC-MS) analyses of N 2 O concentrations in discrete samples from the Southern Ocean and showed agreement to within the 2 % measurement uncertainty of the GC-MS method. The equilibrator response time to concentration changes in water was from 142 to 203 s, depending on the headspace flow rate. The system was tested at sea during a north-to-south transect of the Atlantic Ocean. While the subtropical gyres were slightly undersaturated, the equatorial region was a source of nitrous oxide to the atmosphere, confirming previous findings (Forster et al., 2009)

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Section: Gc-ms Measurements Of Discrete Samplessupporting

confidence: 56%

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Grefe

Kaiser

2014

Ocean Sci.

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“…Profile data from the North Atlantic [35] suggest there is no significant N 2 O production this deep. However, assuming even that true North Atlantic subsurface production amounts only to half of what is predicted by our method would change the global production estimate only by approximately 5 per cent.…”

Section: (D) Integrated Production Estimatesmentioning

confidence: 95%

Global oceanic production of nitrous oxide

Freing

Wallace

Bange

2012

Phil. Trans. R. Soc. B

143

151

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We use transient time distributions calculated from tracer data together with in situ measurements of nitrous oxide (N 2 O) to estimate the concentration of biologically produced N 2 O and N 2 O production rates in the ocean on a global scale. Our approach to estimate the N 2 O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We estimate that the oceanic N 2 O production is dominated by nitrification with a contribution of only approximately 7 per cent by denitrification. This indicates that previously used approaches have overestimated the contribution by denitrification. Shelf areas may account for only a negligible fraction of the global production; however, estuarine sources and coastal upwelling of N 2 O are not taken into account in our study. The largest amount of subsurface N 2 O is produced in the upper 500 m of the water column. The estimated global annual subsurface N 2 O production ranges from 3.1 + 0.9 to 3.4 + 0.9 Tg N yr 21. This is in agreement with estimates of the global N 2 O emissions to the atmosphere and indicates that a N 2 O source in the mixed layer is unlikely. The potential future development of the oceanic N 2 O source in view of the ongoing changes of the ocean environment (deoxygenation, warming, eutrophication and acidification) is discussed.

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“…For the first time in the Namibian upwelling system, N 2 O samples were collected off Walvis Bay at around 23 • S during the FRS Africana cruise in December 2009 within the framework of the GENUS project (Geochemistry and Ecology of the Namibian upwelling system). The collected samples were poisoned with mercuric chloride onboard and measurements were done after the cruise at IFM-GEOMAR, Germany, by using the static equilibration method according to Walter et al (2006). All data enumerated above will be compared to simulations outputs for the same geographical positions (except for DON because there are no available measurements in the Namibian upwelling system) and the same climatological months.…”

Section: Data Usedmentioning

confidence: 99%

Coupled physical/biogeochemical modeling including O<sub>2</sub>-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela

et al. 2013

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Abstract. The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e.g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this model in a 3-D realistic coupled physical/biogeochemical configuration in the Namibian upwelling system (northern Benguela) using the high-resolution hydrodynamic ROMS model. We present here a validation using in situ and satellite data as well as diagnostic metrics and sensitivity analyses of key parameters and N2O parameterizations. The impact of parameter values on the OMZ off Namibia, on N loss, and on N2O concentrations and emissions is detailed. The model realistically reproduces the vertical distribution and seasonal cycle of observed oxygen, nitrate, and chlorophyll a concentrations, and the rates of microbial processes (e.g, NH4+ and NO2− oxidation, NO3− reduction, and anammox) as well. Based on our sensitivity analyses, biogeochemical parameter values associated with organic matter decomposition, vertical sinking, and nitrification play a key role for the low-oxygen water content, N loss, and N2O concentrations in the OMZ. Moreover, the explicit parameterization of both steps of nitrification, ammonium oxidation to nitrate with nitrite as an explicit intermediate, is necessary to improve the representation of microbial activity linked with the OMZ. The simulated minimum oxygen concentrations are driven by the poleward meridional advection of oxygen-depleted waters offshore of a 300 m isobath and by the biogeochemical activity inshore of this isobath, highlighting a spatial shift of dominant processes maintaining the minimum oxygen concentrations off Namibia. In the OMZ off Namibia, the magnitude of N2O outgassing and of N loss is comparable. Anammox contributes to about 20% of total N loss, an estimate lower than currently assumed (up to 50%) for the global ocean.

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Nitrous oxide in the North Atlantic Ocean

Abstract: Abstract. In order to get a comprehensive picture of the distribution of nitrous oxide (N 2 O) in the North Atlantic Ocean, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and cold-

Cited by 83 publications

References 51 publications

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Global oceanic production of nitrous oxide

Coupled physical/biogeochemical modeling including O<sub>2</sub>-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela

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Nitrous oxide in the North Atlantic Ocean

Abstract: Abstract. In order to get a comprehensive picture of the distribution of nitrous oxide (N 2 O) in the North Atlantic Ocean, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and cold-

Cited by 83 publications

References 51 publications

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Equilibrator-based measurements of dissolved nitrous oxide in the surface ocean using an integrated cavity output laser absorption spectrometer

Global oceanic production of nitrous oxide

Coupled physical/biogeochemical modeling including O&lt;sub&gt;2&lt;/sub&gt;-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela

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Product

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Coupled physical/biogeochemical modeling including O<sub>2</sub>-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela