Late Quaternary Glacier response to humidity changes in the arid Andes of Chile (18-29°S)

Today, no glaciers exist between 18 degrees 30 'S and 27 degreesS, even on mountains much higher than 6000 in. These dry high-mountain environments are very sensitive to changes in climatic boundary conditions, particularly humidity since temperatures are far below freezing. Here we present a reconstruction of climatic changes since the Last Glacial Maximum for the Chilean dry Andes of the southern hemisphere. We reconstructed regional equilibrium line altitudes (ELA) for three different moraine stages, representing extensive past glaciations in this currently unglaciated region. Comparison of the regional pattern of the ELA with modem climate conditions allows us to draw implications about the paleoclimatic conditions during the best preserved 'moraine stage II' glaciations in the northern as well as in the southern part of the research area. Our results suggest humid conditions in the northern part (18-24 degreesS) during Late Glacial times, with strongly increased convective precipitation during austral summer. The temporal-coincidence of glaciers in the mountains and high lake levels on the Altiplano (Tauca Phase) is evident. To the south, no simple shift of the Westerlies is implied by our glacier reconstructions. The northern limit of effective moisture for glacier formation did not shift significantly, but stayed in the area of the present day northernmost glaciers of the Westerlies at about 27 degreesS. But further south, precipitation increased significantly, accompanied by at least 2-3 degreesC colder conditions. The age of this glaciation is uncertain, but probably of Late Glacial or Last Glacial Maximum (LGM) times. Overall, glaciers in the dry Andes of South America clearly responded to large changes in the humidity, not primarily the temperature regime, with all its consequences on the environment (hydrology, vegetation, etc.), illustrating the different regional responses to global climatic change. (C) 2001 Elsevier Science B.V. All rights reserved.