ASTRONOMICAL FORCING OF CONTRASTING RAINFALL CHANGES IN TROPICAL SOUTH-AMERICA BETWEEN 12,400 AND 8800 CAL YR BP

Today, precipitation over tropical South America is largely controlled by the seasonal movements of the Inter-Tropical Convergence Zone (ITC Z), During the summer, the ITCZ is shifted southward due to the warmin g of the continent. Paleoclimate data from southeastern Amazonia and t he central Andes indicate that these two areas evolved similarly durin g the last 30,000 yr. However, between 12,400 and 8800 cal yr B.P., ea stern Amazonia received substantial moisture whereas the Bolivian Alti plano was arid. This suggests that the ITCZ during summer was then far ther north than it is today. (C) 1997 University of Washington.