Reconstructing palaeoenvironments using variations in the isotopic composition of bison tooth enamel carbonate from Saskatchewan archaeological sites
Lack of calibrated instruments and written records prior to European contact in North America has forced palaeoclimatic researchers to develop various proxies capable of reconstructing ancient environments. Stable isotope analysis of tooth enamel of large terrestrial herbivores has increasingly become a creditable method of determining the ancient environments which these large mammals occupied during life. Archaeological evidence indicates human inhabitants of the northern Great Plains relied heavily on bison procurement throughout much of the Holocene. Because of this correlation, stable isotope analysis of bison tooth enamel has the capability of informing on palaeoenvironmental conditions which these ancient cultural groups occupied for the last 10,000 years on the northern Great Plains. Decades of research has provided evidence that stable isotope analysis of tooth enamel of large bodied herbivores (e.g. bovids) has the potential to be used as a proxy for reconstructing palaeoclimate, palaeoecology, foraging strategies and herd behaviour. Oxygen (δ 18O) isotope ratios are used as a proxy to track the meteoric hydraulic cycle (i.e. precipitation), which in turn is driven by local surface temperatures. Carbon (δ13C) isotope ratios have the ability to indicate photosynthetic pathways used by plant species, thus indicating local terrestrial plant cover. Dietary intake of water (δ 18O) and food (δ13C) are associated with isotopic signals which are recorded in the tooth enamel of a bison during amelogenesis (tooth enamel formation). Once tooth enamel is formed it never remodels; therefore, isotopic ratios recovered from fossil enamel become an archive of dietary consumption. In general, δ 18O isotope ratios are used to determine surface water and surface temperature conditions, whereas δ13C isotope values are used to indicate the abundance of C3 to C4 grasses consumed during an animal’s life. This study analyzes stable isotope (δ 18O and δ13C) ratios obtained from fossil bison enamel associated with archaeological sites in the northern Great Plains (Saskatchewan) region. The purpose of this study is to create a comparative model used to indicate ancient seasonality and palaeoenvironmental conditions over a 9,000 year period in the Holocene. A total of eight archaeological sites were examined, with each site representing a distinct time period and an affiliated human culture. In addition, isotope (δ 18O and δ13C) ratios recovered from tooth enamel was compared to isotope (δD and δ13C) values previously (Leyden 2004) examined from bone collagen of bison remains from the same archaeological sites. Results of this study demonstrates that original isotopic values from consumed water (δ 18O) and food (δ13C) from archaeological bison tooth enamel reflects seasonal changes for an approximate 18 month period. Further, results from this study also indicate that several climate and plant ecology changes occurred in the Saskatoon, Saskatchewan region over the last 9,000 years. Episodes of climate warming and cooling have been inferred by changes in δ 18O ratios at different time periods of the Holocene. Similarly, significant differences are also detected in δ13C values from different archaeological sites, inferring that bison populations consumed various abundances of C4 grasses at different time periods. In addition, evidence from this study has indicated that stable isotope ratios from enamel (δ 18O) and collagen (δD) from the same archaeological site, for the purpose of inferring climate conditions, demonstrate differing data for several time periods and close correlations for others. On the contrary, δ13C from both tooth enamel and bone collagen from each archaeological site produce comparable data which were used to measure the abundance of C4 grasses consumed by bison population during particular time periods.
Bison, Stable Isotopes, Teeth, Oxygen, Carbon, Holocene, Northern Great Plains
Master of Arts (M.A.)
Archaeology and Anthropology