n-Alkane deuterium analysis of soil samples from South Africa

The hydrogen isotope composition of plant leaf wax (dDwax) has been found to record the isotope composition of precipitation (dDp). Hence, dDwax 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 dDwax data from soils along vegetation gradients and climatic transects in southern Africa to investigate the impact of different environmental factors on dDwax. We found that dDwax correlated significantly with annual dDp (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 dDwax, while vegetation change was of minor importance. In contrast, we found that δDwax did not correlate with annual dDp 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 dDwax and dDp in this region. Our findings have implications for palaeoenvironmental investigations using dDwax in southern Africa. In the summer rain dominated eastern and central region, dDwax should serve well as a qualitative palaeohydrological recorder. In contrast, the processes influencing dDwax 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.