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| Titel |
Evidence for efficient regenerated production and dinitrogen fixation in nitrogen-deficient waters of the South Pacific Ocean: impact on new and export production estimates |
| VerfasserIn |
P. Raimbault, N. Garcia |
| 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 ; 5, no. 2 ; Nr. 5, no. 2 (2008-03-05), S.323-338 |
| Datensatznummer |
250002369
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| Publikation (Nr.) |
 copernicus.org/bg-5-323-2008.pdf |
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| Zusammenfassung |
| One of the major objectives of the BIOSOPE cruise, carried out on the R/V
Atalante from October-November 2004 in the South Pacific Ocean, was to
establish productivity rates along a zonal section traversing the
oligotrophic South Pacific Gyre (SPG). These results were then compared to
measurements obtained from the nutrient – replete waters in the Chilean
upwelling and around the Marquesas Islands. A dual 13C/15N isotope
technique was used to estimate the carbon fixation rates, inorganic nitrogen
uptake (including dinitrogen fixation), ammonium (NH4) and nitrate
(NO3) regeneration and release of dissolved organic nitrogen (DON). The SPG
exhibited the lowest primary production rates (0.15 g C m−2 d−1),
while rates were 7 to 20 times higher around the Marquesas Islands and in
the Chilean upwelling, respectively. In the very low productive area of the
SPG, most of the primary production was sustained by active regeneration
processes that fuelled up to 95% of the biological nitrogen demand.
Nitrification was active in the surface layer and often balanced the
biological demand for nitrate, especially in the SPG. The percentage of
nitrogen released as DON represented a large proportion of the inorganic
nitrogen uptake (13–15% in average), reaching 26–41% in the SPG, where
DON production played a major role in nitrogen cycling. Dinitrogen fixation
was detectable over the whole study area; even in the Chilean upwelling, where
rates as high as 3 nmoles l−1 d−1 were measured. In these
nutrient-replete waters new production was very high (0.69±0.49 g C m−2 d−1)
and essentially sustained by nitrate levels. In the
SPG, dinitrogen fixation, although occurring at much lower daily rates
(≈1–2 nmoles l−1 d−1), sustained up to 100% of the
new production (0.008±0.007 g C m−2 d−1) which was two
orders of magnitude lower than that measured in the upwelling. The annual
N2-fixation of the South Pacific is estimated to 21×1012g,
of which 1.34×1012g is for the SPG only. Even if our "snapshot"
estimates of N2-fixation rates were lower than that expected from a
recent ocean circulation model, these data confirm that the N-deficiency
South Pacific Ocean would provide an ideal ecological niche for the
proliferation of N2-fixers which are not yet identified. |
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