Temperature dependence of oxygen isotope acid fractionation for modern and fossil tooth enamels.
The oxygen isotope ratio of CO(2) liberated from structural carbonate in tooth enamel apatite was measured at phosphoric acid reaction temperatures of 25 degrees C, 60 degrees C and 90 degrees C, and it was found that apparent acid fractionation factors for pristine enamel, fossilized enamel, and calcite follow different temperature relationships. Using sealed vessel reactions normalized to alpha(25) = 1.01025 (the fractionation factor for calcite at 25 degrees C), the apparent fractionation factor at 90 degrees C (alpha*(90)) for pristine enamel ranged between 1.00771 and 1.00820, and between 1.00695 and 1.00772 for fossilized enamel. Apparent fractionation factors for common acid bath reactions are similar to those for sealed vessel reactions. A significant correlation exists between alpha*(90) and F(-) content, suggesting that change in the acid fractionation factor may be related to the replacement of OH(-) with F(-) during fossilization of bioapatite. These results have important implications for making accurate comparisons between modern and fossil tooth enamel delta(18)O values, and for the uniformity of isotope data produced in different laboratories using different acid reaction temperatures.
Passey
Benjamin H
BH
Department of Geology and Geophysics, University of Utah, 135 S. 1460 E. Rm 719, Salt Lake City, UT 84112, USA. passey@earth.utah.edu
Cerling
Thure E
TE
Levin
Naomi E
NE
D000818:Animals; D003743:Dental Enamel / Q000737:chemistry*; D005553:Forensic Dentistry / Q000379:methods; D005580:Fossils; D013058:Mass Spectrometry / Q000379:methods*; D010103:Oxygen Isotopes / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013696:Temperature
D010103:Oxygen Isotopes