Late Quaternary environmental change in southern Africa

Abstract

Over the last 400 000 years, the pattern of climatic change in the southern African sector of the southern hemisphere is shown to have followed in broad outline that defined by the Vostock ice-core sequence. Regional-local differences are apparent in the inshore ocean sediment core record taken from the continental shelf off Namibia and probably relate to little-understood local processes. Clear evidence of precessional Milankovitch forcing of climate is evident for the subcontinent over the last 200 000 years. The Last Glacial Maximum was coof and dry over most of non-equatorial southern Africa, when the semi-permanent subtropical anticyclone dominating the atmospheric circulation was displaced equatorward. At the time, Lake Victoria was dry. Post-glacial warming culminated in the Holocene altithermal, which reached its maximum earlier than 6000 BP. Lake Victoria began to fill rapidly and overflowed at around 7500 BP. Rapid speciation of local fishes occurred in the lake at an unprecedented rate. Over the last 6000 years, robust, spatially representative high-resolution speleothem records from the summer rainfall region of the southern part of the subcontinent reveal that a high degree of variability prevailed on centennial to decadal scales. Abrupt changes, often over decades, are a feature of the record. Whereas maximum heating in the altithermal occurred before 6000 BP, the greatest extent of grass cover characterized the landscape at around 2400-2000 BP. In the last six millennia, the most pronounced and sustained event was the five centuries of cooling during the Little Ice Age from AD 1300 to 1800.