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Coccolithophores on the North-West European Shelf: calcification rates and environmental controls

Coccolithophores on the North-West European Shelf: calcification rates and environmental controls
Coccolithophores on the North-West European Shelf: calcification rates and environmental controls
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.
1726-4170
3919-3940
Poulton, A.J.
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Stinchcombe, M.C.
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Achterberg, E.P.
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Bakker, D.E.
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Dumousseaud, C.
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Lawson, H.E.
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Lee, G.A.
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Richier, S.
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Suggett, D.J.
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Young, J.R.
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Poulton, A.J.
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Stinchcombe, M.C.
433dd398-15f7-4730-9f1e-992d65bec70b
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9
Bakker, D.E.
49d46b0f-d823-4416-b1f9-deb2debedafd
Dumousseaud, C.
31cc4879-0d45-4674-8eba-93105ee25c2e
Lawson, H.E.
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Lee, G.A.
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Richier, S.
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Suggett, D.J.
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Young, J.R.
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Poulton, A.J., Stinchcombe, M.C., Achterberg, E.P., Bakker, D.E., Dumousseaud, C., Lawson, H.E., Lee, G.A., Richier, S., Suggett, D.J. and Young, J.R. (2014) Coccolithophores on the North-West European Shelf: calcification rates and environmental controls. Biogeosciences, 11 (14), 3919-3940. (doi:10.5194/bg-11-3919-2014).

Record type: Article

Abstract

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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Submitted date: January 2014
Accepted/In Press date: February 2014
Published date: 25 July 2014
Organisations: Marine Biogeochemistry, Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 360942
URI: http://eprints.soton.ac.uk/id/eprint/360942
ISSN: 1726-4170
PURE UUID: a6d85cd8-2ecf-4b69-8f5f-0d58a46909bf
ORCID for C. Dumousseaud: ORCID iD orcid.org/0000-0001-5995-902X

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Date deposited: 07 Jan 2014 13:38
Last modified: 25 Jun 2024 01:42

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Contributors

Author: A.J. Poulton
Author: M.C. Stinchcombe
Author: E.P. Achterberg
Author: D.E. Bakker
Author: C. Dumousseaud ORCID iD
Author: H.E. Lawson
Author: G.A. Lee
Author: S. Richier
Author: D.J. Suggett
Author: J.R. Young

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