Abstract
The hydrogen isotope composition of plant leaf wax (dD wax) has been found to record the isotope composition of precipitation (dD p). Hence, dD wax is increasingly used for palaeohydrological reconstruction. It is, however, also affected by secondary factors, such as vegetation type, evapotranspiration and environmental conditions, complicating its direct application as a quantitative palaeohydrological proxy. Here, we present dD wax data from soils along vegetation gradients and climatic transects in southern Africa to investigate the impact of different environmental factors on dD wax. We found that dD wax correlated significantly with annual dD p (obtained from the interpolated Online Isotopes in Precipitation Calculator data set) throughout eastern and central South Africa, where the majority of the mean annual precipitation falls during the summer. We found evidence for the effect of evapotranspiration on dD wax , while vegetation change was of minor importance. In contrast, we found that dD wax did not correlate with annual dD p in western and southwestern South Africa, where most of the annual precipitation falls during winter. Wide microclimatic variability in this topographically variable region, including distinct vegetation communities and high vegetation diversity between biomes as well as a potential influence of summer rain in some locals, likely compromised identification of a clear relationship between dD wax and dD p in this region. Our findings have implications for palaeoenvironmental investigations using dD wax in southern Africa. In the summer rain dominated eastern and central region, dD wax should serve well as a qualitative palaeohydrological recorder. In contrast, the processes influencing dD wax in the winter rain-dominated western and southwestern South Africa remain unclear and, pending further analyses, potentially constrain its use as palaeohydrological proxy in this region.