TRENDS IN CLIMATE AND VEGETATION OF PLIO-PLEISTOCENE SOUTH AFRICA: USING FOSSIL ENAMEL ISOTOPIC DATA TO ADDRESS QUESTIONS OF REGIONAL ENVIRONMENTAL CHANGE

The Plio-Pleistocene climate transition is associated with significant changes in ocean-atmospheric circulation and continental climates. Today, the vegetation diversity of southern Africa is influenced by the cold Benguela Current to the west and the warm Agulhas Current to the east. Marine proxy records indicate that the distinct vegetation and climate zones of S. Africa (winter rainfall vs. summer rainfall) have existed for more than 5 Myr. In this study, we expand the record of S. African climate change on the continents using isotope data from fossil teeth. Although, in S. Africa, the isotopic records of fossil teeth have traditionally be used to reconstruct the environmental context of human evolution, they are an untapped resource for investigating climate change in S. Africa during the last 5 Myr.

We present isotopic data from the carbonate (δ¹³C_carbonate, δ¹⁸O_carbonate) of >100 fossil teeth from Langebaanweg (5 Ma) and Elandsfontein (1.0 – 0.6 Ma), Western Cape, S. Africa. The diagenetic integrity of these isotopic data is demonstrated by the δ¹⁸O offset between carbonate and the more strongly bonded phosphate of the enamel (8.80 ± 0.54‰, n = 50) which is similar to that in modern samples, suggesting excellent preservation of enamel and providing confidence in the d¹⁸O and d¹³C values.

New and published fossil enamel isotopic data from 8 sites across S. Africa spanning the last 5 Myr indicate sustained C₃ vegetation and winter rainfall along the west coast amidst a general trend of increased aridity, concurrent with sustained, though increased upwelling of the Benguela Current. Isotopic data from the east indicate a sustained summer rainfall with C₃ and C₄ vegetation and expanding C₄ grasslands since the Pliocene, concurrent with a sustained Agulhas Current. Isotopic data from the interior, the summer rainfall zone, suggest eastward shifts in winter rainfall and periods of a higher proportion of C₃grasses in the late Quaternary.

Despite large spatial and temporal gaps, enamel isotopic records from S. Africa generally are consistent with the vegetation and climate trends observed in marine cores off the coasts of S. Africa. Our results show that enamel isotope datasets can serve as useful tools for evaluating how terrestrial environments in S. Africa responded to broader changes in Plio-Pleistocene climates.