Chilean Lake District): Introduction

J Paleolimnol (2008) 39:151–161 DOI 10.1007/s10933-007-9113-2 ORIGINAL PAPER A 17,900-year multi-proxy lacustrine record of Lago Puyehue (Chilean Lake District): introduction Marc De Batist Æ Nathalie Fagel Æ Marie-France Loutre Æ Emmanuel Chapron Received: 2 October 2006 / Accepted: 29 April 2007 / Published online: 27 July 2007 Ó Springer Science+Business Media B.V. 2007 Abstract This paper introduces the background measurements, identification of event-deposits, and and main results of a research project aimed at varve-counting for the past 600 years. The core unravelling the paleolimnological and paleoclimato- extends back to 17,915 cal. yr. BP, and the seismic logical history of Lago Puyehue (408 S, Lake data indicate that an open-lake sedimentary envi- District, Chile) since the Last Glacial Maximum ronment already existed several thousands of years (LGM), based on the study of several sediment before that. The core was submitted to a multi-proxy cores from the lake and on extensive fieldwork in analysis, including sedimentology, mineralogy, the lake catchment. The longest record was obtained grain-size, major geochemistry and organic geo- in an 11-m-long piston core. An age-depth model chemistry (C/N ratio, d13C), loss-on-ignition, mag- was established by AMS 14C dating, 210Pb and 237Cs netic 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 This is the first in a series of eight papers published in this fluctuations superimposed on a long-term warming special issue dedicated to the 17,900 year multi-proxy trend. Identified climate fluctuations confirm a.o. the lacustrine record of Lago Puyehue, Chilean Lake District. The existence of a Late-Glacial cold reversal predating papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre and E. Chapron. the northern-hemisphere Younger Dryas cold period by 500–1,000 years, as well as the existence of an M. De Batist (&) early southern-hemisphere Holocene climatic opti- Renard Centre of Marine Geology, Universiteit Gent, mum. Varve-thickness analyses over the past 9000 Gent, Belgium 600 years reveal periodicities similar to those e-mail: [email protected] associated with the El Ninõ Southern Oscillation N. Fagel and the Pacific Decadal Oscillation, as well as Clays and Paleoclimate Research Unit, University intervals with increased precipitation, related to an of Lie`ge, Lie`ge, Belgium intensification of the El Ninõ impact during the M.-F. Loutre southern-hemisphere equivalent of the Little Ice Institut d’Astronomie et de Geóphysique Georges Age. Lemaıˆtre, Universite´ catholique de Louvain, Louvain-la-Neuve, Belgium Keywords Lake Á Deglaciation Á Late Glacial Á E. Chapron Holocene Á South America Á Paleoclimate Á Geological Institute, ETH Zu¨rich, Zu¨rich, Switzerland Paleolimnology 123 152 J Paleolimnol (2008) 39:151–161 Introduction Some of the most spectacular natural climate fluctuations of the past 18,000 years occurred during the transition from the last glacial into the current interglacial period, and were characterized by rapid, drastic, millennium-scale temperature excursions (Stocker 2003). Although these climate changes are recorded in various natural archives in both hemispheres, it remains still unclear how and to what degree and extent the various climate systems of the Earth interacted during these periods (e.g. Sirocko 2003; Vandergoes et al. 2005). Different studies using ice-core data from Greenland and from different areas in the Antarctic have suggested both synchronous and asynchronous relationships between the climates of both hemispheres (e.g. Blunier et al. 1998; Steig et al. 1998). Recent investigations have shown that the southern hemisphere may play a greater role in the regulation of the global climate than previously thought and that it actually may have triggered some of the major climate changes during the past glacial–interglacial period (Knorr and Loh- mann 2003; Ribbe 2004). This contrasts with previ- ous hypotheses and highlights the need for additional, well-dated, high-resolution post-LGM (Last Glacial Fig. 1 Regional location map of the Chilean Lake District, with indication of the main lakes and volcanoes Maximum) paleoclimate data from the Southern Hemisphere (Broecker 2003). More in particular, high-resolution and well-dated climate reconstruc- the region of the Chilean Lake District particularly tions are urgently needed in the mid- to high-latitude interesting to investigate spatio-temporal patterns in regions in the South (i.e. between 40 and 708 S) to past climate variability using a paleolimnological reveal the extent and duration of Southern Hemi- approach. sphere climate fluctuations and the connection In this volume, we present the results of a first between the Northern and Southern Hemispheric multi-disciplinary investigation of the sedimentary climate systems (e.g. Sirocko 2003; Stocker 2003). record of the paleolimnological and paleoclimatolog- Southern South America is particularly well ical changes that affected one of the lakes in the suited to produce valuable paleoclimate records Chilean Lake District: Lago Puyehue (408 S). This for the study of interhemispheric linkages through- study is the first in the region to provide a fully out the Late Quaternary, given its location in the continuous, high-resolution, lacustrine record and as Southern Westerly zone (40–558 S), which is such it contributes to the growing network of influenced by both equatorial and Antarctic climate paleoclimate studies in the area, which up to now expressions. Especially South-Central Chile, situ- comprise essentially geomorphological and strati- ated at the windward side of the Andes, is highly graphic studies of deglacial terrestrial sediment sensitive to variations in the position and intensity sequences (e.g. Denton et al. 1999; Bennett et al. of these Southern Westerlies (Moreno et al. 2001). 2000; Lowell et al. 1995), palynological studies of The continuous distribution of large lakes across a peatbog sequences (e.g. Moreno et al. 1999), or wide latitudinal belt (Fig. 1) at the northern studies of oceanographic records (e.g. Lamy et al. boundary of the Southern Westerly zone makes 2004). 123 J Paleolimnol (2008) 39:151–161 153 Study area the Andes, which was covered by the Northern Patagonian Ice Cap during Quaternary glaciations, The Chilean Lake District and terminate at the piedmont of the mountains, at the boundary with the Central Valley (Fig. 1). The The Chilean Lake District extends from ca. 378 to maximum extension of the glaciers is marked by 428 S (Fig. 1). At this latitude, Chile is about 200 km well-developed moraine complexes. There are two wide and it can be sub-divided from West to East into main generations of moraines that mark the maxi- three main physiographic provinces (Fig. 1): the mum extension of the Patagonian Ice Cap during the Coastal Ranges, the Central Valley and the Andes. ultimate and penultimate glaciations, locally called The Coastal Ranges, on average 500–800 m high, are the Llanquihue and Casma or Colegual glaciations, composed of a Late Paleozoic accretionary prism and respectively. Three successive Llanquihue moraine magmatic arc (Willner et al. 2004) and are dominated belts are clearly visible in the morphology throughout by primarily low-grade metamorphic rocks. The the Lake District (Laugenie 1982). They document Central Valley has a mean altitude of 150–200 m different glacial stages, and have been (radiocarbon)- and consists of Eocene-Miocene volcano-sedimen- dated at ca. 73–65 kyr BP, ca. 28–18 kyr BP and ca. tary deposits that are overlain by Pliocene-Quaternary 15–14 kyr BP (Clapperton 1993). The youngest and volcanics and volcanoclastics and by fluvial and most internal ones often function as dams for the fluvioglacial deposits. The Andes, at an average several large glacial piedmont-type lakes that char- elevation of 2,500–1,500 m, consist of plutonic acterize the area. basement and volcanic rocks, resulting from Pliocene In total, the Lake District comprises up to 17 to Recent volcanic activity (SERNAGEOMIN 2003). medium- to large-sized lakes (Fig. 1). They range This outspoken physiographic segmentation is a from about 5 to 45 km across and are on average direct result of the subduction of the Nazca oceanic between 100 and 350 m deep. In general, they show a plate below the adjacent continental margin (Fig. 1). distinct tendency of increasing in size and depth and Ongoing subduction is also reflected in the distribu- decreasing in altitude from North to South. The tion of the seismicity, with very frequent and strong pioneering work of H. Campos and his co-workers in earthquakes. The largest ever instrumentally recorded the ‘80s has uncovered the general characteristics of earthquake, the Valdivia earthquake of 22 May 1960, their morphology and bathymetry and has illustrated devastated large parts of the area and reportedly even that most of the lakes are composed of a complex triggered an eruption of the Puyehue Volcano, at combination of several sub-basins separated by 70 km distance (Lara et al. 2004). shallower ridges or sills. The subduction-related geodynamic setting also The limnology of these lakes has been studied by makes this area one of the most active volcanic a.o. Campos et al. (1987, 1988, 1989, 1990, 1992a, regions in the World. It is part of the South American 1992b) and Urrutia et al. (2000). They are all South Volcanic Zone (SVZ) and comprises a whole oligotrophic and temperate monomictic, with a series of very large and highly active volcanoes summer stratification from December to March (Fig. 1): e.g. the Llaima (3,060 m), Villarrica (slightly variable depending on altitude). (2,847 m), Osorno (2,652 m) and Puyehue Volcanoes (2,111 m).

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