USING OXYGEN ISOTOPIC ANALYSES OF BISON TOOTH ENAMEL AS A PROXY FOR RECONSTRUCTING THE OXYGEN ISOTOPIC RATIOS OF SURFACE WATER

The oxygen isotopic values of bones and teeth from mammals often tracks the oxygen isotopic composition of surface water and/or precipitation, and thus may be used to reconstruct paleoclimatic changes. However, the isotopic values of different mammals taxa display different relationships to the oxygen isotopic values of surface water. Thus, before the isotopic values of a fossil taxa can accurately interpreted, we must first determine what isotopic patterns are displayed by a taxa’s modern equivalent. I therefore analyzed the distribution and variability of the oxygen isotope ratios of modern bison (Bison bison) from North America. Bison have great potential for providing information about paleoenvironmental conditions in North America, since bison remains are abundant in Holocene and Pleistocene deposits across much of the continent.

I analyzed the oxygen isotopic ratios of carbonate from bulk samples of tooth enamel from modern bison. Teeth were collected from 11 sites located in California, Montana, Oklahoma, Nebraska, North Dakota, South Dakota, Utah, and Wyoming. I examined the variability of oxygen isotopes within and among different populations and compared the average oxygen isotopic values of each population to previous measurements of the average values of local surface waters. I found that the oxygen isotopic values of individual bison within a given population vary less than 5‰; average standard deviations for a population was 1.2‰ (1σ). No significant differences in variability were found among bison populations from different environments. Although individuals within a population displayed a range of values, the average oxygen isotopic values of bison enamel showed a good correlation with the values of local surface waters (R² > 0.8, p < .05). Therefore, analyzes of the average oxygen isotopic values of bison tooth enamel should serve as a good proxy for reconstructing the oxygen isotope ratios of local surface waters.