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

A technique is described whereby the delta(13)C and delta(18)O 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 delta(18)O 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 parts per thousand for both delta(13)C and delta(18)O. The spatial resolution is 200 mu m 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 (alpha CO3-laser) is 1.0071 for biogenic apatite at 38 degrees C determined using the in situ laser. Comparison of delta(18)O(CO3) and delta(18)O(laser) analyses with delta(18)O(laser) and delta(18)O(PO4) results suggest a fractionation factor alpha(CO3-PO4) of 1.0083. Variations in the delta(18)O and delta(13)C 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 delta(13)C and delta(18)O 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.