Oxygen isotope analysis of animal bone phosphate: Method refinement, influence of consolidants, and reconstruction of palaeotemperatures for Holocene sites

Abstract

A new method to isolate phosphate from bones for oxygen isotope analysis was developed and tested. A graphite-reduction technique introduced by O'Neil et al. (1994; Israel Journal of Earth Sciences 43, 203-212) is much simpler and quicker than conventional fluorination techniques and was refined in this study. Problems that may arise during the preparation of bone tissue with high organic content were solved by adding two steps of pre-treatment to remove organic substances before complete dissolution of the bone. The reproducibility of δ18O values is very good, not only for commercial silver phosphate (±0·25‰) and synthetic hydroxyapatite (±0·22‰) but also for modern and fossil bones with different degrees of preservation (±0·16‰). Interlaboratory comparisons were made with NIST-120c, NIST-120b, and the University of Michigan Standard-1. The values for all standards are in good agreement with values obtained both with conventional fluorination and the graphite-reduction method (δ18O(p): 21·7; 20·0; 12·2‰ versus SMOW, respectively). Additionally, the influence of consolidants on the preparation and oxygen isotope analysis was investigated. This investigation was deemed necessary, because fragile and brittle animal remains from archaeological and palaeontological sites are often preserved with these materials before samples can be taken for isotopic analysis. Modern and fossil bones of different degrees of preservation were treated with Mowilith, Shellac, Zaponlack, and Ponal, and subsequently, oxygen isotope analyses were performed in the normal way. No measurable effect of these consolidants was observed on the analyses for δ18O(p). The new procedure has been successfully used to analyse oxygen isotope ratios of cattle and pig bones from Holocene archaeological sites in different climate zones. Calculations of the δ18O values of meteoric water and of mean temperatures using the δ18O(p) values illustrate that isotopic compositions of bones from these terrestrial mammals reflect the climatic conditions of their environment very precisely. (C) 2000 Academic Press.