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| Titel |
What prevents nitrogen depletion in the oxygen minimum zone of the eastern tropical South Pacific? |
| VerfasserIn |
B. Su, M. Pahlow, H. Wagner  , A. Oschlies |
| 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 ; 12, no. 4 ; Nr. 12, no. 4 (2015-02-24), S.1113-1130 |
| Datensatznummer |
250117826
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| Publikation (Nr.) |
 copernicus.org/bg-12-1113-2015.pdf |
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| Zusammenfassung |
| Local coupling between nitrogen fixation and denitrification in
current biogeochemical models could result in runaway feedback in
open-ocean oxygen minimum zones (OMZs), eventually stripping OMZ
waters of all fixed nitrogen. This feedback does not seem to operate
at full strength in the ocean, as nitrate does not generally become
depleted in open-ocean OMZs. To explore in detail the possible mechanisms that
prevent nitrogen depletion in the OMZ of the eastern tropical South
Pacific (ETSP), we develop a box model with fully prognostic cycles
of carbon, nutrients and oxygen in the upwelling region and its
adjacent open ocean. Ocean circulation is calibrated with
Δ14C data of the ETSP. The sensitivity of the
simulated nitrogen cycle to nutrient and oxygen exchange and
ventilation from outside the model domain and to remineralization
scales inside an OMZ is analysed. For the entire range of model
configurations explored, we find that the fixed-N inventory can be
stabilized at non-zero levels in the ETSP OMZ only if the
remineralization rate via denitrification is slower than that via
aerobic respiration. In our optimum model configuration, lateral
oxygen supply into the model domain is required at rates sufficient to
oxidize at least about one fifth of the export production in the model
domain to prevent anoxia in the deep ocean. Under these conditions,
our model is in line with the view of phosphate as the ultimate
limiting nutrient for phytoplankton, and implies that for the
current notion of nitrogen fixation being favoured in N-deficit
waters, the water column of the ETSP could even be a small net
source of nitrate. |
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