Chilean Lake District): Introduction

Home , Llanquihue glaciation, Southern Chile

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 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 Deglaciation Late Glacial E. Chapron Holocene South America Paleoclimate 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 previous 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).

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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). Many of these are quite recent in age (i.e. Lago Puyehue Late-Glacial to Holocene). Most are stratovolcanoes composed of basaltic to andesitic lavas and pyroc- Lago Puyehue (408400 S, 728280 W) is one of the lastics. The volcanic activity in this part of Chile is so medium-sized moraine-dammed piedmont lakes of pervasive that the whole region is covered by a thick the Lake District. It is located at the foothill of the layer of volcanic ashes, on top of which the typical Andes (Figs. 1 and 2) at an elevation of 185 m a.s.l. andosoils (so-called ‘‘trumaos’’) have formed (Lang- The lake is bordered at its western margin by a series ohr 1971, 1974). of moraine belts formed during the different stages of Apart from the volcanic activity, also the Quater- the Llanquihue glaciation (Fig. 2; Laugenie 1982; nary glaciations have been very important in shaping Bentley 1997). The innermost moraine ridges have the region. Large glacial valleys drain the interior of been dated as being ca. 16,10012,200 years BP in 123 154 J Paleolimnol (2008) 39:151–161

Fig. 2 Grey-shaded, SRTM-derived Digital Elevation Model (DEM) of Lago Puyehue and its catchment, with indication of drainage network, main rivers, volcanoes and moraine ridges (after Bentley 1997). Location of peatbog Los Mallines is also indicated. Bathymetry of Lago Puyehue is based on Campos et al. (1989); bathymetry of Lago Rupanco is not included

age (Bentley 1997). Lago Puyehue is surrounded by alluvial plain (ca. 3 by 7 km) and a distinct, steep- several active volcanoes (Fig. 2): i.e. the Casablanca sloped delta. Several smaller rivers also flow into the volcano at ca. 20 km to the south-east of the lake lake from the North, South and Southeast (Fig. 2). (1,990 m a.s.l.) and the Puyehue volcano (2,240 m Rio Pilmaiqueń forms the outlet of the lake, which a.s.l.) and its fissural prolongation Cordon de Caulle cross-cuts several of the frontal moraine ridges at ca. 30 km to the east of the lake. The history of the (Laugenie 1982; Bentley 1997) before merging with Puyehue volcano dates back to at least 200 kyr the Rio Bueno and eventually flowing into the (Gerlach et al. 1988). Pacific. There is presently no glacier in the catchment

Lago Puyehue has a surface area (A0)of of Lago Puyehue. The AD/A0 index (catchment to 165.4 km2, a water volume of 12.6 km3 and a lake surface ratio) is large, indicating that the maximum depth of 123 m (Campos et al. 1989). Its sedimentary input into the lake is determined by the bathymetry is highly complex (Fig. 2) and reveals drainage from the catchment and that the infill is three interconnected sub-basins, separated by bathy- dominated by river-borne sedimentation. metric sills or ridges: (1) a large western sub-basin, Lago Puyehue is an oligotrophic and temperate 5 · 12 km across and about 100 m deep, (2) a small monomictic lake. The lake is stratified with a northern sub-basin, 4 · 4 km across and 120 m deep, thermocline at *20 m depth in summer and mixed and (3) a large, irregularly shaped eastern sub-basin, during the austral winter months (Campos et al. 5 · 8 km across and 123 m deep. Several islands (a.o. 1989). The lake temperature (epilimnion) is maxi- Fresia Island, Cuicui Island) cluster in the central and mum in summer (*188C) and water mixing in winter eastern part of the lake (Fig. 2). They consist of leads to a 9–108C homothermy. Maximum nutrient bedrock and their surface is characterized by glacial concentrations (phosphorus and nitrogen) occur in striae and grooves (Laugenie 1982). autumn and winter (Campos et al. 1989). Its high 2 The catchment area (AD) covers 1,510 km , and silica concentration (15 mg/l; Campos et al. 1989)is extends far to the East from the lake (Fig. 2) into the characteristic for lakes located in volcanic setting. Andes. It consists of Quaternary volcanic rocks, Phytoplankton (e.g. Melosira, Asterionella) is more Pleistocene glacial and fluvioglacial deposits and abundant in austral autumn and winter (Campos et al. isolated outcrops of Mesozoic and Cenozoic intru- 1989); phytoplankton other than diatoms (e.g. Cyan- sions, and it is quasi totally covered by several metres ophyceae) is dominant in austral summer months. of post-glacial andosoils. The lake’s main tributary is Climate around Lago Puyehue is characterized by the Rio Golgol, which enters the lake at its eastern temperate, humid conditions and is largely controlled border (Fig. 2). Here, the river has developed a large by the strength and position of the westerly winds.

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Mean annual air temperature in the catchment varies main sedimentary environments in the lake. A first between 6 and 98C, with maxima of 208C in January, coring site (i.e. PU-I: 40839.7660 S, 72822.1550 W, and minima of 28C in July (Schick 1980). Freezing 122.4 m water depth) was selected on the basin floor sometimes occurs at night in winter, but complete ice in the deep eastern sub-basin, in front of the steep- covering of the lake has never been observed sloped delta of the Rio Golgol, and a second site (i.e. (Thomasson 1963). Snow cover occurs from May to PU-II: 40841.8430 S, 72825.3410 W, 48.8 m water November, and the current Equilibrium Line Altitude depth) on the elevated platform in the southern part of lies at 1,7001,600 m a.s.l. (Laugenie 1982; Hubbard the lake, far away from the main sources of 1997). Winds are strongest during the transition from terrigenous input and shielded from mass-wasting austral autumn to winter (*4 m/s in May) and during and turbidite activity. The seismic data indicated that winter. In spring, wind speeds are lower and reach on both locations the sedimentary infill was contin- only ca. 1 m/s (Kalnay et al. 1996). Precipitation uous, uninterrupted and non-disturbed and thus most trends follow those of the wind velocity and precip- susceptible to hold a valuable paleoclimate signal. itation peaks during the transition from austral Selection of the coring locations was further sup- autumn to winter (450–520 mm in May and June) ported by a series of 6 short sediment cores across the and during winter (Miller 1976; Heusser 2003). basin (Fig. 3). These cores, taken with the UWITEC Annual precipitation increases with elevation, from gravity corer of the Universite´ de Savoie (Chambe´ry, ca. 2,000 mm/year around the lake up to ca. France), served to corroborate the seismic interpre- 5,000 mm/year on the slopes and summits of the tations and to evaluate the importance of possible volcanoes in the region (Parada 1973). During El spatial variations in the sedimentary signal through- Ninõ years precipitation and wind speeds during out the basin. summer months are significantly lower than during The long cores were taken with the UWITEC piston normal climate conditions. corer of the Universite´ de Savoie. The PU-II core has a The humid temperate climate is responsible for the total composite length of 1,122 cm; recovery in the development of dense, temperate rainforests, which PU-I core was restricted to only 236 cm. are essentially of the Valdivian and North-Patagonian Short and long cores were scanned for magnetic type (e.g. Moreno and León 2003; Moreno 2004). susceptibility and gamma-density with a GEOTEK Natural vegetation is still well preserved in the multi-sensor core logger on non-opened sections. catchment; only the shores of Lago Puyehue have Whole-core magnetic susceptibility was re-measured been affected by human activities. at higher resolution on open sections with a Barting- ton MS2E point sensor every 5 mm (Charlet et al. 2007; Bertrand et al. 2007) (see Table 1). Sediment cores Most subsequent analyses have focused on the short cores (Bertrand et al. 2005) and on the PU-II The study of how the lake and its catchment have long core, because of the quality of its record and its reacted to changes in climate and regional environ- length. It was sampled for sedimentological, miner- ment since the retreat of the glacier from the basin alogical and geochemical analysis (Bertrand et al. and of how the lake sediments have recorded those 2007), and for pollen and diatom studies (Vargas changes has essentially focused on two long sediment et al. 2007; Sterken et al. 2007). The lithology cores from key locations in the lake (Fig. 3). consists predominantly of finely laminated to homo- The coring locations were selected based on the geneous brown silty sediment, mainly composed of results of an exploratory seismic and sediment diatoms, organic matter, amorphous clays, crystalline sampling survey (Fig. 3). A seismic network of 47 minerals and volcanic glasses, typical for calm- and high-resolution (300 J sparker) and very high-resolu- open-water lacustrine sedimentation (Bertrand et al. tion (3.5 kHz sub-bottom profiler) reflection seismic 2007). This background sedimentation is locally profiles (total length: 138 km) helped to map the lake- interrupted by a few interbedded turbidite layers floor morphology and the main basin configuration and by several coarse-grained tephra layers, which (Charlet et al. 2007), to delineate the location of each represent distinct pulses of increased terrigenous faults, steep slopes, deltas, etc., and to identify the input (Bertrand et al. 2007; Boe¨s and Fagel 2007a). 123 156 J Paleolimnol (2008) 39:151–161

Fig. 3 Location map of the sparker and sub-bottom seismic proﬁles and of the short and long coring sites in Lago Puyehue

Table 1 Details of the Site number Latitude Longitude Water depth (m) Core length (cm) short and long cores from Lago Puyehue Short cores PU-SC1 40841.2610 S72827.3370 W 90.0 67 PU-SC2 40842.6450 S72825.3110 W 53.6 76 PU-SC3 40842.4180 S72824.5270 W 110.2 86 PU-SC4 40841.1940 S72824.5210 W 108.7 95 PU-SC5 40839.3020 S72823.4470 W24 PU-SC7 40841.4070 S72822.2610 W 113.5 89 Long cores PU-I 40839.7660 S72822.1550 W 122.4 236 PU-II 40841.8430 S72825.3410 W 48.8 1,122

Nine bulk sediment samples were used for AMS The long-term sedimentary record of Lago 14C dating of the entire PU-II core. In addition, 210Pb Puyehue and 137Cs datings were performed (Arnaud et al. 2006) and event deposits together with annual A reliable chronology is fundamental to any paleo- sediment laminations were used to establish a very climate reconstruction. Bertrand et al. (2007) con- detailed age model for the upper 600 years (Boe¨s and structed an age-depth model from the AMS 14C-dated Fagel 2007a). bulk samples. The oldest AMS 14C date obtained was

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16,063 cal. yr. BP (at 1,012 cm). Average sediment AD 1490 and 1700, coincident with the onset of the rates derived from the age-depth model range Little Ice Age (LIA) in Europe (Bertrand et al. 2005). between 1.58 and 0.36 mm/year. The highest sedi- The same combination of proxies is applied to the mentation rates (1.58 mm/year) are observed in the long record of the PU-II core to examine the long-term top 57 cm of the core. They are confirmed by varve trends in the evolution of precipitation and temperature counting and varve-thickness analysis (Boe¨s and in the area (Bertrand et al. 2007). The data suggest a Fagel 2007a) and by 210Pb and 137Cs datings (Arnaud number of climate fluctuations that are superimposed et al. 2006), even if difficulties can arise when on a gradual and continuous climate improvement interpreting Pb-profiles in highly dynamic sedimen- since the LGM: (1) an abrupt warming and reduction in tary environments such as in Lago Puyehue (Arnaud precipitation at the end of the LGM at 17,300 cal. yr. et al. 2006). The lowest sedimentation rates BP; (2) a gradual cooling starting at about 16,000 cal. (0.36 mm/year) occur in the core section just below: yr. BP and culminating in a well-marked cold and i.e. between 57 and 152 cm. This decrease in average humid interval at 13,10012,300 cal. yr. BP; (3) a sedimentation rate is also observed in the varve- rapid warming and drying between 12,300 and thickness record (Boe¨s and Fagel 2007a). Below 11,800 cal. yr. BP, marking the onset of the Holocene; 152 cm, average sedimentation rates become rather (4) a warm and dry period between 11,800 and uniform and vary only between 0.51 and 0.87 mm/ 7,800 cal. yr. BP; and (5) an interval of cold and/or year. Extrapolation of the sedimentation rate beyond humid conditions at 3,4002,900 cal. yr. BP, synchro- the lowest AMS 14C date yields an age of 17,915 cal. nous with a period of low solar activity. The timing of yr. BP for the base of the core. the 13,10012,300 cal. yr. BP cold interval is roughly Such a long, continuous record clearly has the similar to that of the Huelmo/Mascardi Cold Reversal potential to contain very valuable information about (Hajdas et al. 2003) that was identified in the Huelmo the expression and timing of important climate Mire (41.58 S, Chile) and in Lago Mascardi (418 S, fluctuations during the LGM and Late-Glacial period Argentina), both located at nearly the same latitude as in the Lake District. However, the age of the base of Lago Puyehue. This Late-Glacial cold reversal is the core contradicts previous work, which established interpreted as the local counterpart of the northern- that the Lago Puyehue glacier did not retreat from the hemisphere Younger Dryas cold period, and the Lago current lake basin before ca. 14,600 cal. yr. BP Puyehue record thus provides additional support to the (Bentley, 1997), and therefore causes some contro- idea that this southern-hemisphere event precedes the versy. Charlet et al. (2007) discuss the implications of northern-hemisphere Younger Dryas by 500– this apparent discrepancy between the previous 1,000 years. The identification of a warm and dry terrestrial and the new lacustrine records, and use period between 11,800 and 7,800 cal. yr. BP confirms seismic-stratigraphic observations to illustrate that the existence of an early Holocene climatic optimum in open lacustrine sedimentary environments probably the southern hemisphere (e.g. Moreno 2004; Masson even already existed for several thousands of years et al. 2000; Williams et al. 2004; Ciais et al. 1992). before 17,915 cal. yr. BP. The pollen record from Lago Puyehue (PU-II core)

As indicated by the high AD/A0 index, sediment and a pollen profile obtained from the Los Mallines accumulation in Lago Puyehue is essentially precip- peatbog (730 m altitude; Fig. 2) were investigated by itation-controlled. Sedimentological, mineralogical Vargas et al. (2007), in order to reconstruct past and geochemical parameters are thus powerful tracers ecological and climatic conditions and changes in the of changes in terrigenous sediment input but also of Puyehue catchment. The data show that cold, humid changes in nutrient-supply-controlled lake productiv- conditions persisted until 15,500 cal. yr. BP and were ity driven by variations in precipitation. Bertrand followed by a more temperate climate between et al. (2005) investigated the short cores of Lago 15,500 and 14,000 cal. yr. BP, as indicated by pollen Puyehue at very high resolution, and used magnetic assemblages highlighting the arrival of deciduous susceptibility, TiO2 and Al2O3 as proxies for terrig- forest. The period between 14,000 and 11,600 cal. yr. enous supply, and grain size (i.e. diatoms), biogenic BP is marked by a return to cold conditions. The silica, TOC and d13C as proxies for lake productivity. duration of this Late-Glacial cold reversal is signif- They provide evidence for humid conditions between icantly longer than the one expressed in the 123 158 J Paleolimnol (2008) 39:151–161 sedimentological and geochemical proxies (Bertrand the intervals of ca. 80–190 cm, ca. 250–280 cm and et al. 2007). It is followed by warm and dry ca. 460–860 cm; Bertrand et al. 2007). By using thin- conditions between 11,600 and 8,000 cal. yr. BP, section analysis to determine the nature of these reconfirming the existence of an early Holocene laminations, and a statistical evaluation of the climate optimum. This warm period was followed by relationship between the thickness of the laminations temperate, humid to semi-humid conditions until ca. and a series of limnological and local instrumental 500 years ago, after which the present-day cool, climate and weather data, Boe¨s and Fagel (2007a) humid climate conditions took over. demonstrate (i) that these laminations are annual (i.e. Also diatoms are important indicators of past varves, composed of light diatom-rich layers and dark climate conditions. Sterken et al. (2007) investigated diatom-barren layers enriched in terrigenous organic the diatom stratigraphy of Lago Puyehue and recon- matter), and (ii) that their thickness is strongly struct the paleolimnological changes in the basin over controlled by autumn/winter winds and precipitation, the past 17,915 cal. yr. BP. The diatom data do not driving seasonal turn-over and phytoplankton pro- fully corroborate the presence of a Late-Glacial cold ductivity. Moreover, Fagel et al. (2007)finda reversal, although they indicate that some environ- statistically robust correlation between varve thick- mental instability may have occurred between 13,400 ness and El Ninõ Southern Oscillation, suggesting and 11,700 cal. yr. BP. Instead, low absolute abun- that El Ninõ years are not only associated with a dances and biovolumes between 16,850 and precipitation deficit in summer (Montecinos and 12,810 cal. yr. BP suggest an extended period of Aceituno 2003), but also influence autumn/winter low rainfall and/or temperatures. A marked transition precipitations. at 12,810 cal. yr. BP points to an increase in the Boe¨s and Fagel (2007a) examine the variations in moisture supply to the lake, possibly associated with varve thickness for the last 600 years. Their varve- enhanced seasonal variability of the southern Wester- thickness record thus effectively translates into a lies and/or a rise in sea-surface temperatures in the precipitation record at annual resolution. Their data South Pacific. After 9,550 cal. yr. BP, stronger and show: (1) a period with lower precipitation between longer persisting summer stratification can be inferred AD 1400 and 1500, (2) a slightly more humid period from the diatom data, which may have been the result between AD 1500 and 1765, (3) a period with strong of the higher temperatures associated with an early variations in precipitation between AD 1765 and Holocene thermal optimum. The mid-Holocene is 1920, and (4) a period with peak precipitation in the characterized by a decrease in precipitation, culmi- mid 20th century. The relatively dry period between nating around 5,000 cal. yr. BP, and rising again after AD 1400 and 1500 coincides with the late Medieval 3,000 cal. yr. BP. An increase in precipitation from Warm Period (MWP) in Europe, while the subse- 3,000 cal. yr. BP to present could point to an increased quent more humid period (AD 1500–1765) is in good frequency of El Ninõ occurrences, leading to drier agreement with the reconstructions of Bertrand et al. summers and slightly moister winters in the area. (2005), who also identified a period with humid The sedimentary record of Lago Puyehue not only conditions (AD 1490–1700), coincident with the contains important information about the expression onset of the Little Ice Age in Europe. and timing of environmental and climatic changes, In order to identify potential periodicities in the but also of the history of volcanic eruptions and precipitation signal, Fagel et al. (2007) apply a series seismic events (e.g. Chapron et al. 2006; Moernaut of spectral-analysis methods on the 600-year-long et al. 2007), which are continuously altering the varve-thickness record. Their study reveals the pres- landscape in the lake’s catchment. ence of distinct multi-annual (i.e. 2.4, 3.2, 4.4 years) and decadal (15, 41 years) periodicities that are consistent with the main atmosphere-ocean climate The high resolution of the sedimentary record of indexes in the Pacific region: i.e. not only the El Ninõ Lago Puyehue Southern Oscillation (ENSO), but also other southern Pacific indexes, such as the Quasi-Biennal Oscillation A large part of the Lago Puyehue sedimentary record (QBO) and the Pacific Decadal Oscillation (PDO), is laminated (i.e. most of the PU-II long core, except and even some North Pacific oscillations, such as the 123 J Paleolimnol (2008) 39:151–161 159

Pacific Northwest Index (PNI) and the North References Oscillation Index (NOI). This indicates that climate—and especially precipitation—in the region of Arnaud F, Magand O, Chapron E, Bertrand S, Boe¨s X, Charlet F, Me´lie`res M-A (2006) Radionuclide dating (210Pb, Lago Puyehue is strongly influenced by the large- 137 241 Cs, Am) of recent lake sediments in a highly active scale atmosphere-ocean climate patterns of the geodynamic setting (Lakes Puyehue and Icalma—Chilean Pacific Ocean. Moreover, Fagel et al. (2007) find Lake District). Sci Total Environ 366:837–850 that the typical El Ninõ periodicities of 4.4 and Bennett KD, Haberle SG, Lumley SH (2000) The last glacial- 4 years appear much more distinctly in the varve- Holocene transition in Southern Chile. Science 290:325– 328 thickness record during the period between AD Bentley MJ (1997) Relative and radiocarbon chronology of two *1550 and 1820. This time interval corresponds former glaciers in the Chilean Lake District. J Quat Sci roughly to the time-window attributed to the expres- 12:25–33 sion of the LIA in the southern hemisphere (Markgraf Bertrand S, Charlet F, Charlier B, Renson V, Fagel, N (2007) Climate variability of southern Chile since the Last Gla- et al. 2000). The Lago Puyehue varve-thickness cial Maximum: a continuous sedimentological record record therefore suggests that this southern-hemi- from Lago Puyehue (40 8S). J Paleolimnol doi: 10.1007/ sphere LIA is characterized by an intensification of s10933-007-9117-y (this issue) ¨ the El Ninõ impact. Bertrand S, Boes X, Castiaux J, Charlet F, Urrutia R, Espinoza C, Charlier B, Lepoint G, Fagel N (2005) Temporal Finally, Boe¨s and Fagel (2007b) also examine the evolution of sediment supply in Lago Puyehue (Southern laminated lower part of the PU-II long core, in order Chile) during the last 600 years and its climatic signifi- to re-evaluate the exact timing and nature of the last cance. Quaternary Res 64:163–175 ¨ deglaciation and of the Late-Glacial climate changes, Blunier T, Chappellaz J, Schwander J, Dalenbach A, Stauffer TF, Stocker TF, Raynaud D, Jouzel J, Clausen HB, based on varve chronology and varve-thickness Hammer CU, Johnsen SJ (1998) Asynchrony of Antarctic analyses. Their data show two main warming events and Greenland climate change during the last glacial at *17,200 and *15,500 cal. yr. BP marking the end period. Nature 394:739–743 ¨ of the LGM. The Late-Glacial cold reversal, identi- Boes X, Fagel N (2007a) Relationships between southern Chilean varved lake sediments, precipitation and ENSO fied by Bertrand et al. (2007) and—to a lesser for the last 600 years. J Paleolimnol doi: 10.1007/s10933- extent—also in the pollen record of Vargas et al. 007-9119-9 (this issue) (2007), is clearly expressed in the varve-thickness Boe¨s X, Fagel N (2007b) Timing of the late glacial and record as a cold period in two phases between Younger Dryas cold reversal in southern Chile varved sediments. J Paleolimnol doi: 10.1007/s10933-007-9118-x *13,300 and 12,200 cal. yr. BP, interrupted by a dry (this issue) event between *12,800 and 12,600 cal. yr. BP. This Broecker WS (2003) Does the trigger for abrupt climate lends additional support to the existence of a change reside in the ocean or in the atmosphere? Science southern-hemisphere Late Glacial cold reversal (i.e. 300:1519–1522 Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1987) Huelmo/Mascardi Cold Reversal) that precedes the Limnology of Lake Rin˜ihue. Limnolo´gica 18:339–345 northern-hemisphere Younger Dryas by ca. 500 years. Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1988) The transition to significantly warmer climate condi- Limnological study of Lake Llanquihue (Chile). Mor- tions takes place at *11,500 cal. yr. BP. phometry, physics, chemistry, plankton and primary productivity. Arch Hydrobiol 81:37–67 Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1989) Acknowledgements This study was carried out with support Estudios limnologicos en el Lago Puyehue (Chile): from the Belgian Science Policy Office, project ‘‘A morfometria, factores fisicos y quimicos, plancton y pro- continuous Holocene record of ENSO variability in southern ductividad primaria. Med Amb 10:36–53 Chile’’. Many people have been instrumental for the success Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1990) of this project, by providing collaboration, field-work or Limnology study of lake Todos los Santos (Chile). Mor- technical assistance or analytical resources, and by being phometry, Physics, Chemistry, Plankton and Primary available for stimulating discussions and for the sharing of Productivity. Arch Hydrobiol 117:453–484 data and ideas. These people will be acknowledged in the Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1992a) individual papers in this volume. However, we wish to Limnological studies of lake Rupanco (Chile). Mor- address a special word of thanks to our Chilean colleagues phometry, Physics, chemistry, plankton and primary pro- and friends, without whom this project would never have ductivity. Arch Hydrobiol 90(Suppl):85–113 succeeded, and in particular to Mario Pino, Robert Bru¨mmer, Campos H, Steffen W, Aguero G, Parra O, Zuniga L (1992b) Maria Mardones, Roberto Urrutia, Waldo San Martin and Limnology of Lake Ranco (Chile). Limnolo´gica 22:337– Alejandro Penã. 353

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