Stable isotope composition and concentration systematics of Ca and trace elements (Zn, Sr) in single aliquots of fossil bone and enamel

Abstract

Measurements of modern bone and tooth enamel show that calcium stable isotopes (δ44Ca), zinc (δ66Zn), and strontium (δ88Sr) have great potential as ecological and dietary tracers for studies on fossil material. Despite the fact that these three elements can be recovered using sequential chromatographic extraction from a single aliquot, a multi-proxy study has not been attempted yet, which would allow a less destructive analysis of precious fossil material. The present study consists of analyzing δ44Ca, δ66Zn, δ88Sr, and 87Sr/86Sr values in fossil bone and tooth enamel of carnivore and herbivore mammals from the Camiac cave (Upper Pleistocene, Gironde, France). Our study aims at (1) developing a protocol for Ca, Zn, and Sr stable isotope analyses from a single fossil bone or enamel aliquot; (2) testing the respective preservation of biological isotopic signatures in bone and tooth enamel; and (3) comparing the patterning of the different isotopic systems in a fossil mammal community. In the present study, fossil enamel samples have not been leached, as it has been done so far for Zn isotope analyses, but fossil bone samples have been leached using diluted acetic acid or were left unleached. Using inclusive statistical analyses, we identify the effect of leaching on bone chemical compositions, and the concentration and isotope composition of Ca, Zn, and Sr in leached bone and unleached enamel show no sizeable diagenetic overprint. We report for the first time δ66Zn values in fossil bone. The results show that bone δ66Zn values mirror the pattern already observed in enamel, e.g., a significant trophic 66Zn depletion between herbivores and carnivores. Bone δ44Ca and δ88Sr values also mirror those in enamel, and the results highlight a clear distinction between ruminants and non-ruminants, the latter being 44Ca-enriched. The present study focuses on the importance of analyzing several isotopic systems in a single fossil bone or enamel aliquot and shows encouraging results for the preservation of biological isotopic signatures in fossil bone, despite the longstanding dread of a so-called associated pervasive diagenesis. The present study will therefore be useful to consider any precious fossil material with limited destructive sampling possibilities.