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| Titel |
Chemometric perspectives on plankton community responses to natural iron fertilisation over and downstream of the Kerguelen Plateau in the Southern Ocean |
| VerfasserIn |
T. W. Trull, D. M. Davies, F. Dehairs, A.-J. Cavagna, M. Lasbleiz, E. C. Laurenceau-Cornec, F. d'Ovidio, F. Planchon, K. Leblanc, B. Quéguiner, S. Blain |
| 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 (2015-02-18), S.1029-1056 |
| Datensatznummer |
250117822
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| Publikation (Nr.) |
 copernicus.org/bg-12-1029-2015.pdf |
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| Zusammenfassung |
We examined phytoplankton community responses to natural iron fertilisation
at 32 sites over and downstream from the Kerguelen Plateau in the Southern
Ocean during the austral spring bloom in October–November 2011. The community
structure was estimated from chemical and isotopic measurements (particulate
organic carbon – POC; 13C-POC; particulate nitrogen – PN; 15N-PN; and
biogenic silica – BSi) on size-fractionated samples from surface waters (300,
210, 50, 20, 5, and 1 μm fractions). Higher values of 13C-POC (vs.
co-located 13C values for dissolved inorganic carbon – DIC) were taken
as indicative of faster growth rates and higher values of 15N-PN (vs.
co-located 15N-NO3 source values) as indicative of greater nitrate
use (rather than ammonium use, i.e. higher f ratios).
Community responses varied in relation to both regional circulation and the
advance of the bloom. Iron-fertilised waters over the plateau developed
dominance by very large diatoms (50–210 μm) with high BSi / POC ratios,
high growth rates, and significant ammonium recycling (lower f ratios) as
biomass built up. In contrast, downstream polar frontal waters with a similar
or higher iron supply were dominated by smaller diatoms (20–50 μm)
and exhibited greater ammonium recycling. Stations in a deep-water
bathymetrically trapped recirculation south of the polar front with lower
iron levels showed the large-cell dominance observed on the plateau but
much less biomass. Comparison of these communities to surface water nitrate
(and silicate) depletions as a proxy for export shows that the low-biomass
recirculation feature had exported similar amounts of nitrogen to the high-biomass blooms over the plateau and north of the polar front. This suggests
that early spring trophodynamic and export responses differed between
regions with persistent low levels vs. intermittent high levels of iron
fertilisation. |
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