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| Titel |
Modeling the impact of iron and phosphorus limitations on nitrogen fixation in the Atlantic Ocean |
| VerfasserIn |
V. J. Coles, R. R. Hood |
| 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 ; 4, no. 4 ; Nr. 4, no. 4 (2007-07-06), S.455-479 |
| Datensatznummer |
250001847
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| Publikation (Nr.) |
 copernicus.org/bg-4-455-2007.pdf |
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| Zusammenfassung |
| The overarching goal of this study is to simulate subsurface N* (sensu,
Gruber and Sarmiento, 1997; GS97) anomaly patterns in the North Atlantic Ocean
and
determine the basin wide rates of N2-fixation that are required to do
so. We present results from a new Atlantic implementation of a coupled
physical-biogeochemical model that includes an explicit, dynamic
representation of N2-fixation with light, nitrogen, phosphorus and iron
limitations, and variable stoichiometric ratios. The model is able to
reproduce nitrogen, phosphorus and iron concentration variability to first
order. The latter is achieved by incorporating iron deposition directly into
the model's detrital iron compartment which allows the model to reproduce sharp
near surface gradients in dissolved iron concentration off the west coast of
Africa and deep dissolved iron concentrations that have been observed in
recent observational studies. The model can reproduce the large scale N*
anomaly patterns but requires relatively high rates of surface nitrogen
fixation to do so (1.8×1012 moles N yr−1 from
10° N–30° N,
3.4×1012 moles N yr−1 from 25° S–65° N). In
the model the
surface nitrogen fixation rate patterns are not co-located with subsurface
gradients in N*. Rather, the fixed nitrogen is advected away from its source
prior to generating a subsurface N* anomaly. Changes in the phosphorus
remineralization rate (relative to nitrogen) linearly determine the surface
nitrogen fixation rate because they change the degree of phosphorus
limitation, which is the dominant limitation in the Atlantic in the model.
Phosphorus
remineralization rate must be increased by about a factor of 2 (relative to
nitrogen) in order to generate subsurface N* anomalies that are comparable
to the observations. We conclude that N2-fixation rate estimates for
the Atlantic (and globally) may need to be revised upward, which will help
resolve imbalances in the global nitrogen budget suggested by Codispoti et
al. (2001) and Codispoti (2007). |
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