The Potential for High Resolution Climate Records From Ice Deposits in Saline Lakes of the Central Andes

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Layered ice deposits found in shallow saline lakes in southern Bolivia and northern Chile may provide the first high-resolution record of climatic change from the arid-subtropical region of the Andes. The ice deposits rise as much as 7 m above the surface of shallow saline lakes and extend to unknown depths. The deposits are covered by a white carbonate crust and the layers alternate between freshwater ice and ice mixed with sediment. The sites are located in a very arid region (100 mm a.1 mean annual precipitation) where mean annual temperatures range from 3.6o to 9.6oC. The deposits are presently melting, which indicates they are not in equilibrium with the modern climatic regime. Ice cores will be retrieved from the ice deposits beginning with the largest deposit, which is found in Laguna Colorada (22o10'S,4289m), to determine the potential of these deposits as archives of high- resolution climatic change. A transect of cores across the deposits will indicate whether or not the layers are horizontally continuous. The cores will also provide the material for isotopic, chemical, and mineral analyses, which are needed to determine when and how the layers formed. Mono-pulse radar soundings will help to determine how thick the deposits are and the potential need for a mechanical drill to obtain a long record. High lake levels and glacial advances indicate there was a significant change in the hydrologic budget in the subtropical region of the Andes during the late Pleistocene. This change was probably caused by two factors: a southward shift of the Intertropical Convergence Zone, which lengthened the rainy season, and colder temperatures. Pr1eliminary results indicate that the layered ice deposits may have started to form during this late-Pleistocene interval and therefore could provide a unique record of climatic change for this region.