Late quaternary climatic changes in Australia and North Africa: A preliminary interpretation
Abstract Geological and biological data for the period 0–40,000 B.P. suggest that variations in precipitation and evaporation along the temperate and tropical margins of Australia and North Africa are closely related to variations in the position and strength of the subtropical anticyclones. Such changes in the subtropical anticyclones seem related to changes in the position and wave amplitude of the subtropical westerly jet stream. A dynamic interpretation of the inferred palaeoclimates suggests that important additional factors were the distribution of surface temperature anomalies over Siberia and the Sahara at 30,000 B.P.; the location of North Pacific and North American surface temperature anomalies at 24,000 B.P.; compression of the westerlies over Tasmania during 20,000–15,000 B.P.; breakdown of the summer monsoon during 17,000–12,000 B.P.; and a possible change in the slope and nature of the Intertropical Convergence during 11,000–7,000 B.P. Major environmental changes associated with the above influences were heavy rainfall, high lake levels, and increased fluvial activity in southern Australia and along both margins of the Sahara between 40,000 and 20,000 B.P.; low lake levels in the Afar at 30,000 B.P.; intertropical aridity and dune-building along the tropical margins of the Sahara and Australia, and desiccation in semi-arid New South Wales during the interval 17,000–12,000 B.P.; and very high lake levels and increased precipitation in the Sahel and in northern and southern Australia from 11,000 B.P. to 5,000 B.P. The past and present role of the desert anticyclones in controlling the start and the close of the arid phases is demonstrated, as is the correlation between Southern Hemisphere pressure systems and Saharan rainfall, and between Northern Hemisphere circulation changes and Australian rainfall. The subtropical anticyclones may act as buffers when the thermal balance between the two hemispheres is upset by an excess of surface ice in any one hemisphere, and this influences the climate well beyond the deserts.