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| Titel |
Phosphorus speciation and transformation along transects in the Benguela upwelling region |
| VerfasserIn |
Monika Nausch, Günther Nausch, Volker Mohrholz, Martin Schmidt |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088622
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| Publikation (Nr.) |
 EGU/EGU2014-2747.pdf |
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| Zusammenfassung |
| Transformation of phosphate (PO4) introduced by upwelling into the surface was studied in the upper 20 m layer along four transects perpendicular to the coast of Namibia from August 27th to September 15th 2011. Concentrations of inorganic nutrients, dissolved and particulate organic phosphorus (DOP, POP), and particulate organic carbon and nitrogen (POC, PON) were measured and the respective stoichiometry were determined besides measurements of [³³PO4]uptake rates. The fate and interactions of these components are described in relation to both, the distance from the coast and a calculated "pseudoage" of the water masses along perpendicular transects. PO4 decreased from 1.6 µM in the upwelling cell near the coast to 0.4 µM at remote stations. The decrease in PO4 was lower than that of nitrate, resulting in a lower N:P ratio seawards (from 12-16 to 5-9). Based on [³³P]PO4 uptake measurements, a median PO4 turnover time of 57 days corresponding to a distance of about 100 km from the shore, indicated complete PO4 consumption within the transects and thus the need for an additional PO4 supply to sustain the gradient. PO4 depletion was only partially reflected in increasing DOP concentrations. In our bioassays, DOP was produced by heterotrophic bacteria but was mineralized again to PO4 within a few days. Accordingly, PO4 depletion is not evidenced by increasing POP concentrations along the transects. Consistent with declining POC and PON concentrations, produced particulate matter is removed from the upper surface layer and seems to be predominantly transformed in the pelagic layer. Only a small proportion is exported by sedimentation into deeper water layers or to the bottom. In summary, the observed PO4 gradient in the upper 20m surface layer seems to be the result from remineralization and/or input from layers below besides input in the upwelling center. |
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