Oxygen isotopes from turtle bone: Applications for terrestrial paleoclimates?

The oxygen isotope values (delta(p)) of turtle-bone phosphate for two freshwater emydid genera from the United States vary linearly with isotopic values (delta(w)) of environmental water. Mud, box, and snapping turtles do not fall on this regression line, while a soft-shelled turtle and marine loggerhead and leatherback turtles do. Although ectothermic, emydid turtles depend upon bashing to raise their body temperatures. The mean temperature of bone growth is similar (31-33 degrees C) in emydid individuals analyzed as indicated by their bone and body-water oxygen isotopes. Unlike regressions for mammals, the slope of delta(p) versus delta(u) for these emydid turtles is unity, suggesting that the divergence from equilibrium is due to simple fractionation between environmental Loafer and body water: Thus, bone delta(p), values from these genera of turtles land potentially others) may be used to reconstruct Local meteoric water delta(u). values in the fossil record. Concurrent study of fossil freshwater fish or molluscs may then be used to reconstruct local paleotemperatures.