RELATIONSHIP BETWEEN THE HYDROGEN AND OXYGEN ISOTOPES OF DEER BONE AND THEIR USE IN THE ESTIMATION OF RELATIVE-HUMIDITY

The hydrogen isotopic ratio of bone collagen (deltaDb) and the oxygen isotopic ratio of bone phosphate (deltaO-18b) from North American white-tailed deer are each related to both the isotopic ratio of local rain and relative humidity during the growing season. The humidity corrected bone deltaDb and deltaO-18b are highly correlated with each other with a correlation coefficient of 0.962. The regression slope of this equation (8.0) reflects the deltaD vs. deltaO-18 slope of meteoric water when we use a model which assumes that bone oxygen derives from leaf water rather than from drinking or environmental water. Therefore, growing season rain is the likely source of bone H and O. The effects of humidity are significantly greater for deltaO-18b than for deltaDb. Relative humidity (RH) can be estimated with moderate accuracy (+/-6%) from a combination of bone phosphate deltaO-18b and collagen deltaDb and deltaN-15b. This indicates some potential benefits of using fossil bone for evaluating palaeohumidity, The estimate of RH improves to +/-4% when only data from warm climate areas are considered. It appears that for cold climate areas of North America, there may be a discrepancy between the actual leaf water values and the leaf water isotopic values predicted on the basis of the leaf water models used here. It seems possible that the further study of bone isotopic values may lead to a better understanding of how the average leaf water values of an area are related to local environment.