| Stable isotope analyses of the organic and mineral phases sampled from within teeth are increasingly being used to study seasonal dietary variations as well as environmental change. Major limitations for these studies are the sample size required for the isotope analyses, and lack of information about the amount of time represented in the samples. The presented work addressed these problems as follows. (A) Modern plants and sheep/goat dentitions were collected in a region with marked seasonal variation in the vegetation between the wet (C3 plants prevailing) and dry seasons (more C 4 Plants). The delta13Cplants and delta 15Nplants correlate with the rainfall gradient, the delta 13Ccollagen indicates a diet less than 30% C4-plant-based, the highdelta15Nplant variability mask the weaning signal expected in the developing dentition. (B) A new method was developed for sample pretreatment and delta18O analysis of phosphate from biological apatites containing organic matter. Ag3PO 4 was precipitated quantitatively from tooth enamel micro-samples (start size 500 mug) for TC/EA analyses of delta18Ophosphate using a DeltaPlus XL. (C) Sheep kept under controlled conditions received fluorescent-labeled drinking water with different delta18O concentrations. A histology-based sampling strategy was developed to determine the temporal resolution of tooth enamel mineralization and the extent of delta18Ophosphate averaging. This study confirms that enamel secretion rates are not uniform during the development of the second and third molar crowns. The results show that more time is averaged in the conventional sampling strategy (an occluso-cervical series of equivalent sampling volumes) than in a histology-based sampling strategy, and that more than two months are averaged in the former strategy. (D) Electron microprobe and (E) X-ray diffraction analyses were performed to investigate the pattern of tooth enamel mineralization. The results of (C), (D), and (E) confirm an enamel mineralization (maturation) pattern that follows the enamel secretion pattern from occlusal to cervical and from the dentine-enamel junction to the crown surface (contra Suga, 1982). |
