INTRA-TOOTH VARIATIONS IN DELTA-O-18 (PO4) OF MAMMALIAN TOOTH ENAMEL AS A RECORD OF SEASONAL-VARIATIONS IN CONTINENTAL CLIMATE VARIABLES

Regular intra-tooth variations in the delta(18)O value of mammalian to oth enamel phosphate (delta(18)O(p)) have been considered a potential measure of seasonal changes in continental climate variables since the y were first observed. In order to investigate this possibility in mor e detail, analyses were made of teeth from a number of mammalian herbi vores (sheep, cattle, elk, and pigs) that lived over a wide range of g eographic locations, ecological settings, and climatic conditions (Iow a, Florida, Wyoming, Iceland,. England, Croatia, and the Philippines). The lack of intra-tooth delta(18)O(p) variations in teeth of cattle t hat were given tap water to drink provides strong evidence that the un derlying cause of observed intra-tooth variations is primarily a chang e in the isotopic composition of ingested water. In concert with this interpretation, the range of intra-tooth delta(18)O(p) values and thei r absolute values from each locality mirror observed differences in th e range and absolute delta(18)O values of local precipitation (delta(1 8)O(pt)) and in climate variables. Thus intra-tooth delta(18)O(p) valu es can indeed be considered a qualitative measure of seasonal climate change in continental settings. Quantitative use of intra-tooth delta( 18)O(p) values as a climate proxy is possible, but is hindered by lack of detailed information on aspects of mammalian physiology, behavior, and perhaps local hydrology that may also play a role in influencing delta(18)O(p). This problem is exemplified by the different range in d elta(18)O(p) values measured for sheep and cattle from the same locali ty around York, UK (3.4 vs. 2.6 parts per thousand, respectively). The observed difference most likely reflects a difference in the relative amount of leaf water ingested by the two species. Future studies of w ell-constrained samples are required to test physiological models and to develop empirical relations that accurately relate delta(18)O(p) to delta(18)O(pt). In addition to their use as indicators of seasonality , intra-tooth variations in delta(18)O(p) values provide valuable info rmation for longer-term climate change and paleobiological investigati ons. Copyright (C) 1998 Elsevier Science Ltd.