Modern and last local glacial maximum snowlines in the Central Andes of Peru, Bolivia, and Northern Chile

Late Pleistocene snowlines in the central Andes were 500-1200 m lower than at present. Radiocarbon dates imply that the late-Pleistocene glacial maximum in the region occurred prior to 20 C-14 ka, but lack of maximum limiting ages adds considerable uncertainty to the exact timing. Snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central Andes respond differently to temperature and precipitation changes. In the eastern cordillera, the snowline is near the level of the annual 0 degrees C isotherm and melting occurs throughout the year. Here snowlines are sensitive to temperature changes, but relatively insensitive to accumulation changes. In the western cordillera, the snowline rises 1000 higher owing to increasing aridity, and the snowline exhibits a much stronger sensitivity to accumulation changes. The consistent 1200 m snowline depression along the eastern cordilleras of the central Andes can be modeled by a mean annual cooling of 5-9 degrees C. This is inconsistent with the < 2 degrees C cooling in tropical sea-surface temperatures suggested by CLIMAP reconstructions. The 800-1000 m snowline depression in the western cordillera cannot be accounted for solely by cooling, but also requires an increase in precipitation. (C) 1998 Elsevier Science Ltd. All rights reserved.