Stable hydrogen isotopes of bison bone collagen as a proxy for Holocene climate on the Northern Great Plains

Isotopic analyses of fossil and archaeological bison remains can provide information about the biology of prehistoric bison and the ecological conditions in which they lived. Hydrogen isotope ratios (2H/1H, measured as δD) of bison bone collagen should ultimately reflect, through bison diet, those average ratios of local precipitation, which vary systematically according to location and climate. To confirm this, δD values were measured from bone collagen samples collected from geographically distinct populations of modern bison in North America. The δD values of these groups differed in a manner consistent with that of the modern isotopic and climate gradients at each geographic location. Archaeological bison bone samples representing eight temporally distinct populations covering Early, Middle and Late prehistoric age sites from southern Saskatchewan were collected and analyzed. While the mean δD value of each group was consistent with variations in hydrogen isotope composition observable from precipitation in the northern plains, significant differences were found between some of the sampled cohorts. These differences represent climate differences at each of the sampled time periods. The temporal climatic patterns revealed by the δD values of prehistoric bison population bone collagen compares favourably with other models of southern Saskatchewan Holocene climate change as reconstructed using other proxy climate archives. The δD values of bone collagen from prehistoric bison demonstrate a potential for use as a specific paleoclimate proxy which can be directly linked to the 14C age and lifetime of the sampled animal.