Developing bone collagen stable hydrogen isotope analyses for paleoclimate research and enhancing interpretations with bone carbon, nitrogen and oxygen isotopes

Abstract

<p>The hydrogen isotopic ratio δD of rain is known to vary according to climate and temperature. The hydrogen in plant tissue reflects both δD of rain and daytime relative humidity (RH) during the growing season. Since tissue from a herbivorous animal records the δD value of the plants in their diets, δD of herbivore bone collagen should ultimately reflect growing season δD of rain, and to a lesser extent, RH. Therefore, the measurement of δD of non-migratory herbivore bone collagen could have considerable potential for monitoring changes in climate through time and thus prove to be a valuable paleoclimatic tool. In this study, methods for analyzing bone collagen for δD were tested and a means for correcting results for hydrogen exchange was devised. It was found that the δD of bone collagen of North American white tailed deer does indeed reflect both growing season rain δD and RH. With correction for the effects of RH the relationship of bone δD versus summer rain δD has a slope of 1.0 indicating a simple relationship and no unexplained sources of bias. It was also found that δ¹⁵N can be used to correct for the effects of RH so that bone δD can be used to estimate rain δD with good accuracy. The rain δD can then be used to estimate temperature. It was further found that relative humidity can be estimated using both bone collagen δD and bone phosphate δ¹⁸O. Additional work found that the δ¹⁵N of bone collagen of animals consuming some C₄ plants is related to local amount of precipitation whereas no such relationship exists for animals consuming only C₃ plants. δ¹⁵N and δ¹³C were also found to vary considerably across North America which could complicate their interpretation in paleodietary studies.</p>