Climate variability in the Botswana Kalahari from the late Pleistocene to the present day

Noble gas concentrations and oxygen isotopes in groundwaters from the Kalahari Desert in Botswana contain a similar to45 ka paleotemperature record indicating that mean annual temperatures during the period from 24 ka BP to 45 ka BP were 5.2 +/- 1.5degreesC cooler than from similar to16 ka to the present day. In addition to enrichments in oxygen-18, groundwaters recharged after 16 ka BP also contain higher concentrations of excess-air (entrained air bubbles). Taken together, the noble gas, oxygen isotope, and excess-air based paleoclimate archives provide evidence that the high interior desert of southern Africa was both cooler and dryer prior to the Last Glacial Maximum (LGM). Cool, dry conditions also suggest a weaker hydrological cycle in southern Africa. This is contrary to the predicted enhancement of monsoon strength by increased summer insolation in the southern tropics induced by orbital precession during the LGM.