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| Titel |
Coupled physical/biogeochemical modeling including O2-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela |
| VerfasserIn |
E. Gutknecht, I. Dadou, B. Vu, G. Cambon, J. Sudre, V. Garçon, E. Machu, T. Rixen, A. Kock, A. Flohr, A. Paulmier, G. Lavik |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 6 ; Nr. 10, no. 6 (2013-06-03), S.3559-3591 |
| Datensatznummer |
250018270
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| Publikation (Nr.) |
 copernicus.org/bg-10-3559-2013.pdf |
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| Zusammenfassung |
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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