Ratios of cave bear tooth enamel: a record of climate variability during the Pleistocene

Abstract

The oxygen isotope composition of apatitic phosphate in the teeth and bones of certain animals reflects the oxygen isotope composition of the water they ingest. The isotopic composition of meteoric water is, in turn, well-correlated with mean annual temperature so that there is potential for recovering paleotemperatures of the regions where the animals lived. Cave bear teeth have been examined for this purpose. Analyses were made of enamel from 53 canine teeth of cave bears (males, females, adults, and juveniles) from 4 sites in Spain. Phosphate was isolated as Ag3PO4 and reacted with graphite to produce CO2 for isotopic analysis. Reproducibility of the analyses was normally 0.1–0.2‰. The oxygen isotope compositions of teeth from both the coastal site of Cueva de Santa Isabel (350-200 ka) and the inland site of Cueva Mayor (350 ka) were uniform (< 1.4‰ total variation per site) with mean δ18O values of 18.9‰ and 17.2‰, respectively. Interpretations of these data include differences in global temperature between glacial and interglacial periods, and differences due to geographic locations of the sites (e.g., elevation and distance from the sea). The teeth from Cueva del Reguerillo (90-60 ka) in central Spain were more variable in isotopic composition, with an average value between those of teeth from the other caves. Cave bear teeth appear to preserve their original oxygen isotope composition, can be dated, and occur in abundance in many locations of Europe and the Near East. The abundance of the teeth and their large size allows samples used for paleoclimate studies to be restricted to enamel of one type of tooth. The δ18O values of enamel and dentine from one tooth commonly differ. Thus the comparison of oxygen isotope composition among teeth from different individuals, sites, or times, is facilitated if only enamel is used. Restricting analyses to only one type of tooth reduces variability due to changes of diet during the period of tooth growth. The simple evolutionary line of descent of cave bears and the small number of species reduces the effects of interspecific differences in oxygen isotope fractionation. They thus provide a good potential source of material for detailed investigations of Pleistocene climates.