【报告简介】

The δ18O of calcite (δ18Oc) in speleothems from South America is fairly well correlated with austral summer (DJF) insolation, indicating the role of orbitally paced changes in insolation in changing the climate of South America. Using an isotope-enabled atmospheric general circulation model (ECHAM4.6) coupled to a slab ocean model, we study how orbitally paced variations in insolation change climate and the isotopic composition of precipitation (δ18Op) of South America. Compared with times of high summertime insolation, times of low insolation feature (i) a decrease in precipitation inland of tropical South America due to an anomalous cooling of the South American continent and hence a weakening of the South American summer monsoon, and (ii) an increase in precipitation in eastern Brazil that is associated with the intensification and southward movement of the Atlantic Intertropical Convergence Zone, which is caused by the strengthening of African winter monsoon that is induced by the anomalous cooling of northern Africa.