INTER-TOOTH AND INTRA-TOOTH VARIATION IN THE OXYGEN-ISOTOPE COMPOSITION OF MAMMALIAN TOOTH ENAMEL PHOSPHATE - IMPLICATIONS FOR PALEOCLIMATOLOGICAL AND PALEOBIOLOGICAL RESEARCH

Significant differences in the delta(18)O(p) value between teeth, and even within a single tooth were observed in a detailed study of the ox ygen isotope composition of tooth enamel phosphate (delta(18)O(p)) of hypsodont teeth from bison and sheep jaws. The permanent molars and pr emolars of a fossil adult bison from eastern Wyoming (similar to 500 y r B.P.) and a modern sheep from California were analyzed. The bison is assumed to have been free-ranging with a variety of possible water so urces, whereas the sheep was raised on a ranch. Inter-tooth variabilit y in delta(18)O(p) for the bison compared to the sheep (5.6 parts per thousand and 3.5 parts per thousand, respectively) may be a result of behavioral differences. Analyses of multiple samples from the m3 of bo th the bison and sheep vary to a similar degree (3.5 parts per thousan d) in a similar cyclic pattern down the length of the tooth, a pattern which is interpreted to be seasonal. When present, inter- and intra-t ooth variations in delta(18)O(p) are controlled by the water and food ingested by the mammals during the period of enamel formation. In thes e localities, well waters, surface waters, and mother's milk have diff erent isotopic compositions at different times of the year. The data u nderscore the role of biology and behavior in determining delta(18)O(p ) values, and the need to understand how they vary for a population of interest. If these variations are taken into account, the delta(18)O( p) values of single samples from small, late-forming teeth (e.g. premo lars) can be used as a proxy for the delta(18)O value of local meteori c water for long-term climate studies. Multiple samples from a single third molar may provide information on the duration and timing of enam el growth, seasonality, as well as long-term climate change.