MAMMOTH TOOTH ENAMEL OXYGEN AND CARBON STABLE ISOTOPE VARIATION

The carbon and oxygen stable isotope composition of mammoth tooth enamel is used as a proxy for ecological conditions such as vegetation type and temperature. Enamel precipitates from the occlusal (wear) surface to the root possibly over several years, thus providing an ecological proxy spanning multiple seasons. To preserve the fossil, however, only a small number of enamel areas are commonly sampled, so the isotopic variability along the enamel plate is unclear. In this study, we measured variations in the carbon and oxygen stable isotope values in the carbonate component of tooth enamel along enamel plates from five mammoth teeth of poorly known provenance. All enamel plates showed smooth compositional variations along their lengths, but four had standard deviations well above expected analytical reproducibility, reflecting preserved seasonal variation in both oxygen (climate) and carbon (diet). Four teeth had oxygen isotope values between 16.4 and 19.7‰ (V-SMOW) with the fifth tooth values between 14.2 and 15.6‰. These oxygen isotope value differences probably indicate different time periods or geographic areas during tooth growth, since the lower values imply significantly colder conditions. The four larger teeth had carbon isotope values of -7.9 to -11.4‰ (V-PDB), significantly higher than a smaller tooth (-13.3‰ to -11.6‰). The unusually low carbon isotope values from the smaller tooth may reflect milk as a food source since this tooth was likely from a young animal. With analytical errors for oxygen and carbon isotopes of c.0.3‰ and 0.1‰ respectively, zoning up to ~3‰ in both isotopes imply that retrieving the full range of climate and dietary records will require subsampling long sections of teeth or multiple teeth.