Terminal Pleistocene and Holocene dynamics of southern Africa's winter rainfall zone based on carbon and oxygen isotope analysis of bovid tooth enamel from Elands Bay Cave

摘要

Southern Africa's winter rainfall zone (WRZ) is sensitive to changes in the earth's atmospheric and oceanic systems. This region has the potential to provide valuable insight into both regional and global paleoenvironmental dynamics. delta C-13 values of herbivore tooth enamel apatite reflect the proportions of C-3 and C-4 plants consumed. Here we present delta C-13 and delta O-18 values for 86 samples of tooth enamel from grazing and browsing bovids from the terminal Pleistocene and Holocene layers of Elands Bay Cave. The assemblage is dominated by steenbok (Raphicerus campestris) and grysbok (Raphicerus melanotis), which are known to feed on browse if available. However, the assemblage also includes large grazers. This study aims to determine whether the grasses they were eating were purely C-3 (indicating a winter rainfall regime) or included a C-4 component (signaling at least some summer rainfall). Results show that terminal Pleistocene and early Holocene vegetation communities were overwhelmingly C-3. Late Holocene animals show slightly more enriched delta C-13 values, indicating that C-4 grasses and perhaps some CAM plants utilizing C-4 photosynthesis became more common. We infer that late Pleistocene (including the LGM) to early Holocene rainfall was largely restricted to the winter months. In the late Holocene, the increased proportion of C-4/CAM vegetation may be indicative of changes in the position of storm tracks associated with the westerlies. This finding is consistent with other proxy records from southernmost Africa that suggest extension of the growing season into warmer months and/or relatively warmer temperatures during the late Holocene. delta O-18 values from enamel carbonate reflect a complex combination of meteoric drinking water, diet and physiological processes, and vary quite widely within and between species. Browsers have more positive delta O-18 than grazers, because a significant proportion of their moisture intake is from leaves enriched in O-18 as a result of evapotranspiration. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.