Intra-tooth oxygen isotope variation in a known population of red deer: Implications for past climate and seasonality reconstructions

Over the last decade oxygen isotopes from herbivore teeth have frequently been used as a proxy for palaeoclimatic conditions, yet our knowledge of how accurately the isotope signatures of an animal reflect seasonal climatic fluctuations remains limited. Our study on modern red deer from a known location aimed to assess the degree to which seasonal climate changes are reflected in red deer teeth. Our analyses of sequential sub-samples from red deer second and third molars showed that enamel carbonate δ18O values vary within teeth and that the pattern of intra-tooth isotopic variation broadly corresponds to that observed in precipitation δ18O over an annual cycle. The pattern of intra-tooth isotopic variation and absolute values are similar for individuals born in the same year. As the population range in intra-tooth δ18O values closely matches that estimated for the local precipitation and the calculated range in temperature corresponds with that recorded on the Isle of Rum, we conclude that red deer intra-tooth oxygen isotope signatures are a good palaeoclimate and seasonality proxy. In addition, all deer have recorded the lowest δ18O of the cycle (winter minimum) in the same location of the M3 crown, demonstrating the potential utility of this sampling protocol to infer birth seasonality in red deer.