STUDIES OF CARBON, OXYGEN AND STRONTIUM ISOTOPES IN TOOTH ENAMEL: EVALUATING PALEOENVIRONMENTAL CHANGE IN SOUTH AFRICA AND EXPANDING THE PALEOCLIMATE TOOL KIT

Abstract

Anthropogenic-driven climate change has and will continue to influence Earth’s ecosystems and environments. Major regional and global climate events have been observed throughout the geological record. We need to determine how natural systems responded to climate in the past and the possible interactions between mammalian species, including humans, and their environment, if we are to have perspective on how natural systems will respond to changes in climate both currently and in the future. Evaluating past climate and environment can be a useful way to evaluate if and how past landscapes, ecosystems and animal-environment interactions may have been influenced by climatic change. Archeological and paleontological sites along the coastal region of southwestern South Africa preserve fossils and artifacts dating to the Pliocene and Pleistocene (within the last 5 million years). These materials indicate that southwestern South Africa was once home to large herbivorous mammalian communities and that hominins lived here since the mid-Pleistocene, at ca. 1 million years ago. However, this region is currently hot and dry and within a cool growing season. Furthermore, this region is within the fynbos biome, a biome with species that date to before the Pliocene, and is today mostly composed of woody, nutrient-poor shrub land. It is unknown how animals survived in the region during the Pliocene and Pleistocene or the composition of past vegetation and its distribution. Here I present an evaluation of animal diet and the climate and environment of southwestern South Africa over the last 5 million years using the carbon (δ13C values) and oxygen (δ18O values) isotopic composition of fossil teeth. I then evaluate the movement of animals for food in southwestern South Africa during the mid-Pleistocene and the distribution of vegetation at this time using strontium isotope ratios (87Sr/86Sr ratios) in the fossil tooth enamel preserved at archeological site Elandsfontein. I then consider the use of triple oxygen isotopes (∆17O) in the fossil record as a way to improve upon the current δ18O method to determine past climate and environmental change by presenting and characterizing ∆17O in modern tooth enamel. I found that herbivores ate vegetation characteristic of a cool growing season during the Pliocene and Pleistocene, therefore southwestern South Africa was within a winter rainfall zone since at least 5 million years ago. The ecosystem and environment of southwestern South Africa would have had to support the annual growth of grass if large mammalian herbivores (specifically grazers) could have survived in this region. Deposits indicative of fluvial environments (during the Pliocene) and spring-fed environments (during the Pleistocene) are preserved at fossil sites in the region. These environments would have been extremely important for the survival of animals in southwestern South Africa. The 87Sr/86Sr ratios of fossil teeth from mid-Pleistocene Elandsfontein suggest that large herbivores not only stayed within southwestern South Africa for food, but that they did not necessarily leave the area surrounding the fossil site. The ∆17O values of modern tooth enamel samples cover a greater span and include more negative values in arid environments than in humid environments, regardless of the oxygen isotopic composition of meteoric water and latitude. This record indicates the future potential of applying triple oxygen isotopes to the fossil record for reconstructing aridity, atmospheric pCO2 and diagenesis