Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 11, issue 24
Biogeosciences, 11, 7207–7217, 2014
https://doi.org/10.5194/bg-11-7207-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 11, 7207–7217, 2014
https://doi.org/10.5194/bg-11-7207-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 Dec 2014

Research article | 17 Dec 2014

Identifying vital effects in Halimeda algae with Ca isotopes

C. L. Blättler1,*, S. M. Stanley2, G. M. Henderson1, and H. C. Jenkyns1 C. L. Blättler et al.
  • 1University of Oxford, Department of Earth Sciences, Oxford, UK
  • 2University of Hawai`i, Department of Geology & Geophysics, Honolulu, HI, USA
  • *now at: Princeton University, Department of Geosciences, Princeton, NJ, USA

Abstract. Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (−0.6‰) appears to be much smaller than that for the algal aragonite (−1.4‰), similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

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Halimeda algae were used as a test organism to untangle some of the specific factors that influence skeletal composition, in particular Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater. Comparison of the skeletal Ca-isotope ratios with inorganic carbonate forms indicates the effects of mineralogy and Rayleigh distillation of Ca on the geochemistry of their carbonate skeletons.
Halimeda algae were used as a test organism to untangle some of the specific factors that...
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