Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablation

Abstract

A technique is described whereby the δ13C and δ18O values of fossil tooth enamel can be measured in situ using laser ablation techniques. The laser heats the sample and forms CO2 from structural carbonate apatite. The δ18O values obtained with this method are equal to those of the phosphate oxygen due to the high temperature of reaction during ablation. Analytical precision is approximately 0.5‰ for both δ13C and δ18O. The spatial resolution is 200 μm or less, which may be reduced as the technical modifications are made. This method allows the analysis of samples that previously could not be analyzed due to difficulty with sample preparation, size, or rare nature. The apparent oxygen isotope fractionation between the carbonate and laser derived oxygen (αCO3-laser) is 1.0071 for biogenic apatite at 38°C determined using the in situ laser. Comparison of δ18O(CO3) and δ18O(laser) analyses with δ18O(laser) and δ18O(PO4) results suggest a fractionation factor α(CO3)-PO4) of 1.0083. Variations in the δ18O and δ13C values of single teeth can be easily determined with the in situ technique. This will allow the study of changes in diets or water sources during the period of tooth growth, which for larger mammals can be several years for the tooth row. The δ13C and δ18O values are important in paleodiet and paleoecology studies. They can be used to study resource partitioning within an ecosystem and can shed light on the life history strategies within living and extinct species.