Cellular calcium pathways and isotope fractionation in Emiliania huxleyi
- Nikolaus Gussone1,
- Gerald Langer2,
- Silke Thoms2,
- Gernot Nehrke2,
- Anton Eisenhauer3,
- Ulf Riebesell4 and
- Gerold Wefer5
- 1Research Centre Ocean Margins, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany
- 2Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
- 3Leibniz Institute of Marine Sciences at the University of Kiel, Dienstgebäude Ostufer, Wischhofstraße 1-3, 24148 Kiel, Germany
- 4Leibniz Institute of Marine Sciences at the University of Kiel, Dienstgebäude Westufer, Düsternbrooker Weg 20, 24105 Kiel, Germany
- 5Research Centre Ocean Margins, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany
Abstract
The marine calcifying algae Emiliania huxleyi (coccolitho phores) was grown in laboratory cultures under varying conditions with respect to the environmental parameters of temperature and carbonate ion concentration [CO32−] concentration. The Ca isotope composition of E. huxleyi's coccoliths reveals new insights into fractionation processes during biomineralization. The temperature-dependent Ca isotope fractionation resembles previous calibrations of inorganic and biogenic calcite and aragonite. Unlike inorganically precipitated calcite, the [CO32−] concentration of the medium has no significant effect on the Ca isotope composition of the coccoliths. These results indicate a decoupling of the chemical properties of the bulk medium and the calcifying vesicle. Cellular Ca pathways of E. huxleyi indicate that fractionation cannot occur at the crystal surface, as occurs during inorganic precipitation. The dominant processes leading to the observed Ca isotope fractionation pattern in E. huxleyi are most likely the dehydration of the Ca aquocomplex at the plasma membrane and the attachment of dissolved Ca to proteins of Ca channels. The independence of Ca isotope fractionation from [CO32−] and the small temperature dependence of E. huxleyi are also important for defining the isotopic signature of the oceanic Ca sink. Since coccolithophores contribute to about half the global CaCO3 production, a relatively uniform isotopic composition of the oceanic Ca sink is further supported.
Footnotes
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- Accepted 12 March 2006.
- Received 17 February 2006.
- Revision received 10 March 2006.
- Geological Society of America
