Oxygen isotope composition of human teeth and the record of climate changes in France (Lorraine) during the last 1700 years

In order to study climate variations during the last 1700 years in eastern France, fifty-eight oxygen isotope compositions of phosphate were measured in human tooth enamel. The individuals, who lived in Lorraine, are assumed to have drunk local water derived directly from rainfall. According to previous work, drinking water is the main source of oxygen that sets the isotopic composition of phosphatic tissues in humans. The empirical fractionation equation determined from our data combined with those of Longinelli's one [Geochim. Cosmochim. Acta 48 ( 1984) 385] was used to calculate the oxygen isotope composition of meteoric waters. The mean air temperature was inferred from these isotope ratios and the Von Grafenstein et al.' s [ Geochim. Cosmochim. Acta 60 ( 1996) 4025] relationship between delta(18)O and air temperature. Oxygen isotope composition of present-day individuals yields a mean air temperature of 9.9 +/- 1.7 degrees C which is consistent with meteorological data. Application of this method to historical individuals results in mean air temperatures estimates 0 to 3 degrees C higher than present-day air temperature. These warm air temperatures are not realistic during the so-called Little Ice Age for which an air-cooling of about 0.5 to 2 degrees C has been documented. We propose that these relatively high delta(18)O values of human tooth enamel reflect higher mean delta(18)O values of meteoric water which can be attributed to an increased proportion of summer rainfall during the "Little Ice Age" time frame in Lorraine.