Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10-37°C

The oxygen isotope fractionation between the structural carbonate of inorganically precipitated hydroxyapatite (HAP) and water was determined in the range 10-37 degrees C. Values of 1000 ln alpha(CO32--H2O) are linearly correlated with inverse temperature (K) according to the following equation: 1000 ln alpha(CO32--H2O) = 25.19 (+/- 0.53).T-1 - 56.47 (+/- 1.81) (R-2 = 0.998). This fractionation equation has a slightly steeper slope than those already established between calcite and water (O'Neil et al.. 1969, Kim and O'Neil, 1997) even though measured fractionations are of comparable amplitude in the temperature range of these experimental studies. It is consequently observed that the oxygen isotope fractionation between apatite carbonate and phosphate increases from about 7.5 parts per thousand up to 9.1 parts per thousand with decreasing temperature from 37 degrees C to 10 degrees C. A compilation of delta O-18 values of both phosphate and carbonate from modern mammal teeth and bones confirms that both variables are linearly correlated, despite a significant scattering up to 3.5 parts per thousand, with a slope close to I and an intercept corresponding to a 1000 ln alpha(CO32--PO43-) value of 8.1 parts per thousand. This apparent fractionation factor is slightly higher or close to the fractionation factor expected to be in the range 7-8 parts per thousand at the body temperature of mammals. (C) 2009 Elsevier Ltd. All rights reserved.