A 17,900-year multi-proxy lacustrine record of Lago Puyehue (Chilean Lake District): introduction

anglais. peer reviewed

anglais. This paper introduces the background and main results of a research project aimed at unravelling the paleolimnological and paleoclimatological history of Lago Puyehue (40 degrees S, Lake District, Chile) since the Last Glacial Maximum (LGM), based on the study of several sediment cores from the lake and on extensive fieldwork in the lake catchment. The longest record was obtained in an 11-m-long piston core. An age-depth model was established by AMS C-14 dating, Pb-210 and Cs-237 measurements, identification of event-deposits, and varve-counting for the past 600 years. The core extends back to 17,915 cal. yr. BP, and the seismic data indicate that an open-lake sedimentary environment already existed several thousands of years before that. The core was submitted to a multi-proxy analysis, including sedimentology, mineralogy, grain-size, major geochemistry and organic geochemistry (C/N ratio, delta C-13), loss-on-ignition, magnetic susceptibility, diatom analysis and palynology. Along-core variations in sediment composition reveal that the area of Lago Puyehue was characterized since the LGM by a series of rapid climate fluctuations superimposed on a long-term warming trend. Identified climate fluctuations confirm a.o. the existence of a Late-Glacial cold reversal predating the northern-hemisphere Younger Dryas cold period by 500-1,000 years, as well as the existence of an early southern-hemisphere Holocene climatic optimum. Varve-thickness analyses over the past 600 years reveal periodicities similar to those associated with the El Nino Southern Oscillation and the Pacific Decadal Oscillation, as well as intervals with increased precipitation, related to an intensification of the El Nino impact during the southern-hemisphere equivalent of the Little Ice Age.