Quaternary environmental change in the southeast Kalahari, Botswana, southern Africa

The southeastern quadrat of the Kalahari, in common with most of central southern Africa, has few Quaternary palaeoenvironmental sites, and those that exist provide data of poor chronological control, poor continuity, and low time resolution. The situation is particularly acute for the period before the Last Glacial Maximum (LGM). Stable carbon and oxygen isotope analyses of speleothems from Lobatse II Cave in southeast Botswana provide the first continuous palaeoclimatic data for the region, indicating a general decrease in temperature from 50,000 yr BP to the LGM, and episodes with increased rainfall at 49,000, 47,000, 27,000, 25,000 and 23,500 yr BP. The stable carbon isotope record suggests that a significant proportion of the rainfall was of cyclonic origin. Discrepancies between the uranium and radiocarbon series dating of the speleothems suggest that much of the presently available C-14 based data may be inaccurate. However, by adjusting the U-series data from Lobatse to existing information a correlation between winter rainfall episodes in the southeast Kalahari and low lake levels in the middle Kalahari is obtained. This would support a climatic model involving the enhancement of the Southern Oscillation, and an equatorwards displacement of the subtropical convergence. Studies of cores from Lebatse Pan in the southeastern region suggest cycles of accumulation and deflation of pan sediments that would fall within the span of these climatic oscillations.