Multi-isotopic and trace element evidence against different formation pathways for oyster microstructures

Geochimica et Cosmochimica Acta, vol. 308, pp. 326–352

Abstract

Shells of oysters (Ostreidae) are predominantly composed of foliated and chalky calcite microstructures. The formation process of the more porous chalky structure is subject to debate, with some studies suggesting that it is not formed directly by the oyster but rather through microbial mineralization within the shell. Here, this hypothesis is tested in modern shells of the Pacific oyster (Crassostrea gigas) from coastal regions in France and the Netherlands. We combine measurements of stable carbon, oxygen, nitrogen, sulfur, and clumped isotope ratios with high-resolution spatially resolved element (Na, Mg, Cl, S, Mn and Sr) data and microscopic observations of chalky and foliated microstructures in the oyster shells. Our results show no isotopic differences between the different microstructures, arguing against formation of the chalky calcite by microorganisms. However, we observe a small difference in the oxygen isotope ratio (0.32‰) and clumped isotope composition (0.017‰) between the microstructures, which is likely caused by sampling biases due to seasonal differences in growth rate and the short timespan over which the chalky microstructure forms. We therefore recommend sampling profiles through the foliated microstructure to control for strong seasonal variability recorded in the shell which can bias environmental reconstructions. High-resolution (25–50 µm) Na, Mg, Cl, S, Mn and Sr profiles yield empirical distribution coefficients between seawater and shell calcite for these elements. Significant differences in element concentrations and distribution coefficients were confirmed between the two microstructures, likely reflecting differences in mineralization rates or inclusion of non-lattice-bound elements. Only Mg/Ca ratios in the foliated microstructure vary predictably with growth seasonality, and we show that these can be used to establish accurate oyster shell chronologies. The observed effect of mineralization rate on element incorporation into oyster shells should be considered while developing potential element proxies for paleoclimate reconstructions. Trace element proxies in oyster shells should be interpreted with caution, especially when element chemical properties were measured in different microstructures.

Authors 13

1. Niels Jonathan de Winter corresponding

   Vrije Universiteit Brussel · Utrecht University

   Affiliation as printed

   AMGC Research Group, Vrije Universiteit Brussel, Brussels, Belgium

   Dept. of Earth Sciences, Utrecht University, Utrecht, the Netherlands

2. Linda K. Dämmer

   University of Bonn · Royal Netherlands Institute for Sea Research

   Affiliation as printed

   Environmental Geology, Department of Geology, Institute of Geosciences, University of Bonn, Bonn, Germany

   Ocean Systems Department, Royal Netherlands Institute for Sea Research, Texel, the Netherlands

3. Michaela Falkenroth Aachen Neotectonics and Natural Hazards Research Group

   University of Bonn · Royal Netherlands Institute for Sea Research · RWTH Aachen University

   Affiliation as printed

   Environmental Geology, Department of Geology, Institute of Geosciences, University of Bonn, Bonn, Germany

   Neotectonics and Natural Hazards Research Group, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen, Germany

   Ocean Systems Department, Royal Netherlands Institute for Sea Research, Texel, the Netherlands

4. Gert‐Jan Reichart

   Utrecht University · Royal Netherlands Institute for Sea Research

   Affiliation as printed

   Dept. of Earth Sciences, Utrecht University, Utrecht, the Netherlands

   Ocean Systems Department, Royal Netherlands Institute for Sea Research, Texel, the Netherlands

5. Simone Moretti

   Max Planck Institute for Chemistry

   Affiliation as printed

   Max Planck Institute for Chemistry, Otto Hahn Institute, Mainz, Germany

6. Alfredo Martínez‐García

   Max Planck Institute for Chemistry

   Affiliation as printed

   Max Planck Institute for Chemistry, Otto Hahn Institute, Mainz, Germany

7. Nils Höche

   Johannes Gutenberg University Mainz

   Affiliation as printed

   Institute of Geosciences, University of Mainz, Mainz, Germany

8. Bernd R. Schöne

   Johannes Gutenberg University Mainz

   Affiliation as printed

   Institute of Geosciences, University of Mainz, Mainz, Germany

9. Katerina Rodiouchkina

   Ghent University

   Affiliation as printed

   Atomic and Mass Spectrometry - A&MS Research Group, Department of Chemistry, Ghent University, Ghent, Belgium

10. Steven Goderis

    Vrije Universiteit Brussel

    Affiliation as printed

    AMGC Research Group, Vrije Universiteit Brussel, Brussels, Belgium

11. Frank Vanhaecke

    Ghent University

    Affiliation as printed

    Atomic and Mass Spectrometry - A&MS Research Group, Department of Chemistry, Ghent University, Ghent, Belgium

12. Sonja M. van Leeuwen

    Royal Netherlands Institute for Sea Research

    Affiliation as printed

    Coastal Systems Department, Royal Netherlands Institute for Sea Research, Texel, the Netherlands

13. Martin Ziegler

    Utrecht University

    Affiliation as printed

    Dept. of Earth Sciences, Utrecht University, Utrecht, the Netherlands