ALBEDO CHANGES, MILANKOVITCH FORCING, AND LATE QUATERNARY CLIMATE CHANGES IN THE CENTRAL ANDES

Late Quaternary humidity changes resulted in substantial modifications of the land surface characteristics in the Altiplano of the Atacama D esert, central Andes. Reconstructions of surface albedo, top-of-atmosp here (TOA) albedo, and short-wave net radiation in the Andes of northe rn Chile for 20, 14, 10, 7 and 0 ka suggest that surface and TOA albed o increased substantially during periods of relatively humid environme ntal conditions (i.e., with large palaeolakes, glaciers and dense vege tation). The decrease of summer shortwave net radiation and seasonalit y during the late-glacial/early Holocene humid phase (14 to 10 ka) due to Earth's surface and atmospheric characteristics added to the effec t of orbitally driven negative deviations of Southern Hemisphere austr al summer insolation and minimum seasonality at 20 degrees S. Therefor e, in situ radiative forcing is, in contrast to the Northern Hemispher e tropics, not a suitable explanation for enhanced convective precipit ation and, ultimately, humid climatic conditions. Our results suggest that late Quaternary humidity changes on the Altiplano reflect a colle ctive response to (1) environmental changes in the source area of the moisture (e.g., re-expansion of the rain forest and increased release of latent heat over Amazonia and the Chaco, warm sea surface temperatu res in the E Pacific) and, (2) large-scale circulation patterns and wa ve structures in the upper troposphere (strength and position of the B olivian High, divergent flow stimulating convection over the Altiplano ), or that they even reflect a response to (3) interhemispherical tele connections.