Large herbivore δ18O as a proxy for aridity in the South African winter and year-round rainfall zone

Abstract

This study explores patterning in δ18O values of tooth enamel in contemporary African herbivores from mainly C3-dominated ecosystems. Evapotranspiration causes plants to lose H216O to a greater extent than H218O, leaving leaves enriched in 18O. In eastern Africa, ES species (evaporation-sensitive species: those obtaining water from food) tend to have more positive δ18Oenamel values than EI species (evaporation-insensitive species: those heavily dependent on drinking water); the magnitude of the difference increases with increasing aridity. We find the same pattern applies in the winter and year-round rainfall region of southern Africa, allowing us to use δ18Oenamel in fossil animals to examine paleo-aridity. We apply this approach to infer aridity at Quaternary fossil assemblages from present-day winter and year-round rainfall zones, including Elandsfontein (ca. 1–0.6 Ma), Hoedjiespunt (ca. 300–130 ka), and Nelson Bay Cave (23.5–3 ka). This analysis suggests that (1) at various times during the Pleistocene, Elandsfontein and Hoedjiespunt environments were wetter than last glacial maximum (LGM) to Holocene environments at Nelson Bay Cave (year-round rainfall zone); and (2) considered alongside other evidence from the year-round rainfall zone, wetter conditions across the Pleistocene–Holocene transition at Nelson Bay Cave suggests that climate changes at near-coastal sites may be out of phase with the adjacent interior.