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| Titel |
Top-down, bottom-up and physical controls on diatom-diazotroph assemblage growth in the Amazon River plume |
| VerfasserIn |
M. R. Stukel, V. J. Coles, M. T. Brooks, 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 ; 11, no. 12 ; Nr. 11, no. 12 (2014-06-19), S.3259-3278 |
| Datensatznummer |
250117472
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| Publikation (Nr.) |
 copernicus.org/bg-11-3259-2014.pdf |
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| Zusammenfassung |
| The nutrient-rich waters of the Amazon River plume (ARP) support dense blooms
of diatom-diazotroph assemblages (DDAs) that introduce large quantities of
new nitrogen to the planktonic ecosystem and, unlike other nitrogen-fixers,
are likely to directly fuel vertical carbon flux. To investigate the factors
controlling DDA blooms, we develop a five phytoplankton (cyanobacteria,
diatoms, unicellular microbial diazotrophs, DDAs, and
Trichodesmium), two zooplankton model and embed it within a
1/6° resolution physical model of the tropical and subtropical
Atlantic. The model generates realistic DDA blooms in the ARP and also
exhibits basin-wide primary production, nitrogen fixation, and grazing rates
consistent with observed values. By following ARP water parcels with
synthetic Lagrangian drifters released at the river mouth we are able to
assess the relative impacts of grazing, nutrient supply, and physical forcing
on DDA bloom formation. DDA bloom formation is stimulated in the
nitrogen-poor and silica-rich water of the ARP by decreases in grazing
pressure when mesozooplankton (which co-occur in high densities with coastal
diatom blooms) concentrations decrease. Bloom termination is driven primarily
by silica limitation of the DDAs. In agreement with in situ data, this net
growth niche for DDAs exists in a salinity range from ∼20–34 PSU,
although this co-occurrence is coincidental rather than causative. Because
net growth rates are relatively modest, bloom formation in ARP water parcels
depends critically on the time spent in this ideal habitat, with high DDA
biomass only occurring when water parcels spent >23 days in the optimal
habitat niche. |
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