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Removal of organic magnesium in coccolithophore calcite

Removal of organic magnesium in coccolithophore calcite
Removal of organic magnesium in coccolithophore calcite
Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.
0016-7037
226-239
Blanco-Ameijeiras, S.
12b97bf7-375f-44c5-8bac-1dd0efc0b7bd
Lebrato, M.
1c458a19-0f2a-4e52-90e1-66c53a44c73f
Stoll, H.M.
0983a8c4-a2bc-4af5-becc-b774f3e29363
Iglesias-Rodriguez, M.D.
f93f3be3-83b0-46c1-a5f8-e42ad1e30674
Méndez-Vicente, A.
968eb550-f767-47bb-938e-708ab6264e2d
Sett, S.
4e90e5f0-05d7-4e28-a24c-2d5251d5fd9c
Müller, M.N.
b1bba61d-7e2d-4dfd-a1bc-b37bfa3b28c4
Oschlies, A.
1e17ff79-6084-4a56-b130-7d39dcd7568f
Schulz, K.G.
bb1f434a-7223-442d-95d4-c4dbf8346dd1
Blanco-Ameijeiras, S.
12b97bf7-375f-44c5-8bac-1dd0efc0b7bd
Lebrato, M.
1c458a19-0f2a-4e52-90e1-66c53a44c73f
Stoll, H.M.
0983a8c4-a2bc-4af5-becc-b774f3e29363
Iglesias-Rodriguez, M.D.
f93f3be3-83b0-46c1-a5f8-e42ad1e30674
Méndez-Vicente, A.
968eb550-f767-47bb-938e-708ab6264e2d
Sett, S.
4e90e5f0-05d7-4e28-a24c-2d5251d5fd9c
Müller, M.N.
b1bba61d-7e2d-4dfd-a1bc-b37bfa3b28c4
Oschlies, A.
1e17ff79-6084-4a56-b130-7d39dcd7568f
Schulz, K.G.
bb1f434a-7223-442d-95d4-c4dbf8346dd1

Blanco-Ameijeiras, S., Lebrato, M., Stoll, H.M., Iglesias-Rodriguez, M.D., Méndez-Vicente, A., Sett, S., Müller, M.N., Oschlies, A. and Schulz, K.G. (2012) Removal of organic magnesium in coccolithophore calcite. Geochimica et Cosmochimica Acta, 89, 226-239. (doi:10.1016/j.gca.2012.04.043).

Record type: Article

Abstract

Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.

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Published date: 15 July 2012
Organisations: Ocean Biochemistry & Ecosystems

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Local EPrints ID: 341236
URI: https://eprints.soton.ac.uk/id/eprint/341236
ISSN: 0016-7037
PURE UUID: f177fb36-1312-4efd-b92d-b00958415a77

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Date deposited: 18 Jul 2012 09:43
Last modified: 16 Jul 2019 21:58

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Contributors

Author: S. Blanco-Ameijeiras
Author: M. Lebrato
Author: H.M. Stoll
Author: M.D. Iglesias-Rodriguez
Author: A. Méndez-Vicente
Author: S. Sett
Author: M.N. Müller
Author: A. Oschlies
Author: K.G. Schulz

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