Persistent millennial-scale climatic variability over the past 25,000 years in Southern Africa

Abstract

Data from stalagmites in the Makapansgat Valley, South Africa, document regional climatic change in southern Africa in the Late Pleistocene and Holocene. A new TIMS U-series dated stalagmite indicates speleothem growth from 24.4 to 12.7 ka and from 10.2 to 0 ka, interrupted by a 2.5ka hiatus. High-resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated ~17 ka, was interrupted by cooling, probably associated with the Antarctic Cold Reversal, and was followed by strong warming after 13.5ka. The Early Holocene experienced warm, evaporative conditions with fewer C4 grasses. Cooling is evident from ~6 to 2.5ka, followed by warming between 1.5 and 2.5ka and briefly at ~AD 1200. Maximum Holocene cooling occurred at AD 1700. The new stalagmite largely confirms results from shorter Holocene stalagmites reported earlier. The strongest variability superimposed on more general trends has a quasi-periodicity between 2.5and 4.0 ka. Also present are weaker ~1.0 ka and ~100-year oscillations, the latter probably solar induced. Given similarities to the Antarctic records, the proximate driving force producing millennial- and centennial-scale changes in the Makapansgat record is postulated to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex.