Journal article
Removal of organic magnesium in coccolithophore calcite
Geochimica et Cosmochimica Acta, Vol.89, pp.226-239
2012
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Abstract
<p>Coccolithophore calcite refers to the plates of calcium carbonate (CaCO<sub>3</sub>) 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 (H<sub>2</sub>O<sub>2</sub>) were tested on synthetic pellets, prepared by mixing reagent grade CaCO<sub>3</sub> with organic matter from the non-calcifying marine algae <em>Chlorella autotrophica</em> and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH<sub>2</sub>OH·HCl + NH<sub>4</sub>OH)] followed by three consecutive oxidations (using H<sub>2</sub>O<sub>2</sub>) 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 <em>Emiliania huxleyi</em>, <em>Calcidiscus leptoporus</em> and <em>Gephyrocapsa oceanica</em>. 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 (</p>
Details
- Title
- Removal of organic magnesium in coccolithophore calcite
- Creators
- S Blanco-Ameijeiras - University of SouthamptonM Lebrato - Helmholtz Centre for Ocean Research KielH M Stoll - University of OviedoM D Iglesias-Rodriguez - University of SouthamptonA Méndez-Vicente - University of OviedoS Sett - Helmholtz Centre for Ocean Research KielM N Muller - Institute for Marine and Antarctic StudiesA Oschlies - Helmholtz Centre for Ocean Research KielKai G Schulz - Southern Cross University
- Publication Details
- Geochimica et Cosmochimica Acta, Vol.89, pp.226-239
- Identifiers
- 2930; 991012822048002368
- Academic Unit
- Science; Faculty of Science and Engineering; Centre for Coastal Biogeochemistry; School of Environment, Science and Engineering
- Resource Type
- Journal article