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| Titel |
Coccolithophores on the north-west European shelf: calcification rates and environmental controls |
| VerfasserIn |
A. J. Poulton, M. C. Stinchcombe, E. P. Achterberg, D. C. E. Bakker, C. Dumousseaud, H. E. Lawson, G. A. Lee, S. Richier, D. J. Suggett, J. R. Young |
| 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. 14 ; Nr. 11, no. 14 (2014-07-25), S.3919-3940 |
| Datensatznummer |
250117526
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| Publikation (Nr.) |
 copernicus.org/bg-11-3919-2014.pdf |
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| Zusammenfassung |
| Coccolithophores are a key functional group in terms of the pelagic
production of calcium carbonate (calcite), although their contribution to
shelf sea biogeochemistry, and how this relates to environmental conditions,
is poorly constrained. Measurements of calcite production (CP) and
coccolithophore abundance were made on the north-west European shelf to
examine trends in coccolithophore calcification along natural gradients of
carbonate chemistry, macronutrient availability and plankton composition.
Similar measurements were also made in three bioassay experiments where
nutrient (nitrate, phosphate) and pCO2 levels were manipulated.
Nanoflagellates (< 10 μm) dominated chlorophyll biomass and
primary production (PP) at all but one sampling site, with CP ranging from
0.6 to 9.6 mmol C m−2 d−1. High CP and coccolithophore abundance
occurred in a diatom bloom in fully mixed waters off Heligoland, but not in two distinct coccolithophore blooms in the central North Sea and Western
English Channel. Coccolithophore abundance and CP showed no correlation with
nutrient concentrations or ratios, while significant (p < 0.01)
correlations between CP, cell-specific calcification (cell-CF) and irradiance
in the water column highlighted how light availability exerts a strong
control on pelagic CP. In the experimental bioassays, Emiliania-huxleyi-dominated coccolithophore communities in shelf waters (northern
North Sea, Norwegian Trench) showed a strong response in terms of CP to
combined nitrate and phosphate addition, mediated by changes in cell-CF and
growth rates. In contrast, an offshore diverse coccolithophore community (Bay
of Biscay) showed no response to nutrient addition, while light availability or mortality may have been more important in controlling this
community. Sharp decreases in pH and a rough halving of calcite saturation
states in the bioassay experiments led to decreased CP in the Bay of Biscay
and northern North Sea, but not the Norwegian Trench. These decreases in CP
were related to slowed growth rates in the bioassays at elevated pCO2
(750 μatm) relative to those in the ambient treatments. The
combined results from our study highlight the variable coccolithophore
responses to irradiance, nutrients and carbonate chemistry in north-west
European shelf waters, which are mediated by changes in growth rates, cell-CF
and species composition. |
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