HR: 0830h
AN: B31D-0340    [PDF]
TI: Stable Isotope Analyses of Phosphate Oxygen From Micro-samples of Biological Apatite: A new Routine Procedure for Silverphosphate Micro-precipitation and the Removal of Organic Contamination
AU: * Wiedemann-Bidlack, F B
EM: fbidlack@forsyth.org
AF: Dept. of Biomineralization, The Forsyth Institute, 140 The Fenway, Boston, MA 02155 United States
AU: Colman, A S
EM: a.colman@gl.ciw.edu
AF: Geophysical Laboratory, The Carnegie Institution, 5251 Broad Branch Road, Washington, DC 20015 United States
AU: Fogel, M L
EM: fogel@gl.ciw.edu
AF: Geophysical Laboratory, The Carnegie Institution, 5251 Broad Branch Road, Washington, DC 20015 United States
AB: Oxygen isotope analyses in bone and teeth of living and fossil animals are widely used for testing hypotheses about variability of diet and habitat. For the analysis of environmental or dietary changes in the past, tooth enamel has become the preferred study material, because its mineral content is higher than bone and dentine, and the relatively large size of the carbonato-apatite crystals of enamel make it more stable against {\it post mortem} diagenetic alteration than dentine or bone. Intra-tooth sampling of dental enamel is increasingly used for the investigation of seasonal climate variability, taking advantage of both the high correlation between an animal's drinking water and the $\delta$$^{18}$O in its mineralized tissues and the incremental growth pattern of tooth enamel. The different oxygen-containing ions of bioapatite (phosphate, carbonate, and hydroxyl group) incorporate into the mineral lattice at different rates during enamel mineralization, and differ in their susceptibility against {\it post mortem} diagenetic alteration. In addition, it is difficult to account for the different reaction chemistries of phosphate, carbonate, and hydroxyl group using isotope analysis techniques that include all oxygen contained in the enamel (e.g., laser ablation). These problems can be addressed analyzing phosphate oxygen only. However, two major factors limit the potential of $\delta$$^{18}$O analyses in dental enamel: A) the starting sample size for isotope analyzes often precludes the use of small teeth or the intra-tooth sampling of a given tooth; B) Small amounts of biogenic organic material in tooth enamel (less than 1% by wt) can reduce the precision and lead to anomalous analytical results in $\delta$$^{18}$O measurements on Ag$_{3}$PO$_{4}$ produced from tooth enamel. A new procedure was developed for the pre-treatment and $\delta$$^{18}$O analysis of phosphate from small samples (500 $\mu$g) of tooth enamel containing organic matter. Ag$_{3}$PO${4}$ was precipitated quantitatively for analysis of $\delta$$^{18}$O$_{phosphate}$ using a Thermoquest-Finnigan TC/EA coupled to Delta$^{\it Plus}$ XL. A sodium hypochlorite sample pre-treatment step was determined to remove organic matter quantitatively without altering the isotopic composition of the phosphate oxygen. The reproducibility of $\delta$$^{18}$O values for pretreated samples (0.2-0.3 $\permil$, 1$\sigma$) is much better than for samples without pre-treatment (1.2 $\permil$, 1$\sigma$). Phosphate oxygen isotope standards processed using this technique gave measured values indistinguishable from the standard composition, demonstrating the accuracy of the new technique.
DE: 0400 Biogeosciences
DE: 1600 GLOBAL CHANGE (New category)
DE: 1694 Instruments and techniques
SC: Biogeosciences [B]
MN: 2003 Fall Meeting