IWRA Proceedings

AbstractWe present the results of a multiproxy study of an Andean ice core in order to reconstruct regional paleoclimate. In tropical mountain areas, the precipitation storage as snow during the rainy season is crucial. Indeed, the snowmelt provides the precious water needed when the irrigation demand is high during the dry season. Moreover the rivers transport the surplus of water downstream to the plain and the big cities. Consequently the variations of the snow precipitation amount are a determining factor of the subsistence and the development of the populations. In the study region, South America between the equator and 35°S, the consequences of global climatic change are increased by effect of El Niño- Southern Oscillation (ENSO). The Andean glaciers are very sensitive to these fluctuations and are used as modern (glacier monitoring) and past (ice core) climatic archives. Since the 1980’s several ice cores were extracted by American and Swiss teams and by IRD Great Ice in Ecuador, Bolivia, Peru and Chile. To complete the series and in particular to underline the direct impact of climatic change and ENSO over the last decades, a 42 m long core was drilled on Coropuna glacier (Peru, inactive volcano, semi-arid climate, 100 km east of the Pacific Ocean, 6377 m, 15°33´S, 72°36´W) in June 2003. The preliminary results (tritium and lead) showed that the ice core spans the last 100 years. The variations of the stable isotopes (δ18O and δD) in the ice are a good indicator of the variations between wet and dry periods. The isotope signal presents 5 to 7-year long patterns. The variations of the water isotopic composition have been compared with the variations of the precipitation amounts and the temperatures recorded in the last 40 years by the weather stations located around the Coropuna glacier. A modern relationship between these parameters helped us to propose a regional climatic model for the last 100 years. Other proxies like electrical conductivity, chemical and pollen in ice core profile enabled us to refine our climatic conclusions.