Abstract

The most recent IPCC report indicated that the Subtropical Andes (32 degrees-35 degrees S) are one of the world areas undergoing a strong tendency towards more arid conditions due to current climate change. The winter precipitation that falls on the Andes, related to the Southern Westerlies System (SWS), is the main source of water for central Chile and west central Argentina, making it a fundamental socioeconomic resource. The few long-term records of the eastern slope of the Subtropical Andes do not permit establishing the long-term natural climate variability or determining if this trend does or does not respond to natural forcings. This study therefore presents a centennial and sub-centennial scale reconstruction of the paleoenvironmental dynamics of the eastern slope of the Subtropical Andes during the last 3000 cal yrs BP, based on the pollen record of the Laguna Coraz & oacute;n (LCO; 35.13 degrees S; 2200 m a.s.l.), in order to establish the different regional paleoenvironmental scenarios. The sedimentary record (182 cm) is mostly composed of laminated dark brown clay, and includes a 21-24 cm layer preliminarily associated with the 1932 AD eruption of the Quizap & uacute; volcano. The LCO record shows the development of a grass steppe associated with high-Andean shrubs between 3000 and 2440 cal yrs BP, suggesting slightly more humid conditions than present. From 2440 to 1110 cal yrs BP, there was continuous presence of the grass steppe along with high-Andean and Patagonian low shrubs, indicating moderately more humid conditions than today. The development of a grass steppe with low high-Andean shrubs from 1110 to 320 cal yrs BP reflects conditions slightly more humid that at present, showing a progressive decrease in humidity between 900 and 320 cal yrs BP. Since then, environmental conditions were similar to present ones, associated with the climatic variability at sub-centennial timescale. In the last 320 cal yrs BP, the record shows the presence of introduced species as a consequence of the occupation of the valley to raise livestock, and more recently, tourist activities. These environmental/climatic patterns are similar to those recorded for the western slope of the Subtropical Andes for the Late Holocene, indicating a regional forcing related to the winter precipitation associated with the SWS.