Abstract

The Atacama Desert and adjacent central Andes (16°-27° S) are an ideal testing ground for understanding how the tropical easterlies and southern westerlies have interacted during the late Quaternary. Interactions between these wind belts and Andean topography generate strong vegetation gradients that at lower elevations (2100 to 3500 m) are controlled almost exclusively by a few seasonal rainfall events. We have been using rodent middens to reconstruct vegetation and climate over the last 50,000 years in the Atacama. Readily datable with 14C, middens constitute veritable “snapshots” of past desert communities. Northern Atacama (16° S) midden records display remarkably low species richness between 9500-7400 yr BP. Richness experimented a threefold increase at 6700 yr BP remaining relatively high until 3800 yr BP. Middens younger than 1300 yr BP are slightly poorer in annuals and perennials. Latest Pleistocene to early Holocene middens from the central Atacama (22-24° S) indicate diverse plant communities until ~9600-9200 yr BP. Species richness remained low until 7600-7200 yr BP, after which many middens exhibit increased richness until 3200 yr BP, interrupted by an arid event at ~5100 yr BP. Middens < 3200 yr BP generally exhibit lower levels of richness. Pollen and plant macrofossils from a few Holocene middens in the southern Atacama (25-27° S) reveal a stable arid climate, punctuated by a wet event that occurred within the last millennium. Midden evidence for higher rainfall during portions of the Holocene is pervasive throughout the northern and central Atacama. This contrasts with evidence for sustained drought from high Andean lakes. Increased diversity and productivity ~8000-3200 yr BP, however, is evident from Titicaca and Miscanti pollen records. This leads us to conclude that temperature increases during the Holocene may have exerted major controls on lake records whereas midden records reflect changes almost exclusively in precipitation.