Stable oxygen isotopes of dental biomineral: differentiation at the intra- and inter-tissue level of modern shark teeth

Abstract

In situ oxygen isotopic composition of the sandbar shark (Carcharhinus plumbeus) teeth grown at a constant water temperature and salinity were analysed by high precision and high spatialresolution secondary ion mass spectrometry, targeting dental biomineral within the parallel-bundled enameloid (PBE), the tangle-bundled enameloid (TBE) and the dentine. Measured δ¹⁸O values had comparable inter-tissue variability in each tooth analysed. The PBE enameloid had the smallest scatter of oxygen isotope ratios, while the TBE enameloid had slightly higher intra-tissue variation of δ¹⁸O, but similar average values. The dentine had largest variability and lower average δ¹⁸O. The enameloid of shark teeth is therefore recommended as a target biomineral and a preferential biogeochemical reference for environmental and palaeoenvironmental studies.

Keywords::

• biomineral
• bioapatite
• stable oxygen isotopes
• enameloid
• sharks

Acknowledgements

The research was supported by the 7FP Marie Curie Individual Intra-European Fellowship project 274090 “Vertebrate Isotopes and environment”, the Knut and Alice Wallenberg Foundation Grant (Prof. Per E. Ahlberg, Uppsala University, Sweden), and the NordSIM facility (Swedish Museum of Natural History) which is supported by the research councils of Denmark, Norway and Sweden, the Geological Survey of Finland and the Swedish Museum of Natural History. The authors are particularly grateful to Per E. Ahlberg and Benjamin P. Kear (Uppsala University, Sweden) for their active support to this project, and Micahel M. Joachimski (University of Erlangen-Nuremberg, Germany) for his help with determining the value of Durango apatite standard. The authors thank Julie A. Trotter (University of Western Australia) for her indispensible advices while establishing the experimental protocol, Ivan J. Sansom (University of Birmingham, UK) and senior ecologist Scott Blaker (Blackpool Sea Life Center, UK) for providing the shark teeth, Lev Ilyinsky and Kerstin Lindén for the experimental assistance at the NORDSIM Ion Microprobe Laboratory (Swedish Museum of Natural History, Stockholm) and Plamen S. Andreev (University of Birmingham, UK) for advices on neoselachian dental histology. Torsten Vennemann and Henning Blom are greatly acknowledged for their detailed review and valuable comments, which have significantly improved the quality of this paper. This article is a contribution to the International Geosciences Programme IGCP 591 project. This is NordSIM contribution number 352.