ARTICLE IN PRESS Quaternary International 161 (2007) 4–21 A 14 kyr record of the tropical Andes: The Lago Chungara´ sequence (181S, northern Chilean Altiplano) A. Morenoa,Ã, S. Giraltb, B. Valero-Garce´ sa,A.Sa´ ezc, R. Baod, R. Pregoe, J.J. Pueyoc, P. Gonza´ lez-Sampe´ riza, C. Tabernerb aPyrenean Institute of Ecology—CSIC, Apdo 202, 50080 Zaragoza, Spain bInstitute of Earth Sciences ‘Jaume Almera’-CSIC, C/Lluı´s Sole´ i Sabarı´s s/n, 08028 Barcelona, Spain cFaculty of Geology, University of Barcelona, C/Martı´ Franque´s s/n, 08028 Barcelona, Spain dFaculty of Sciences, University of A Corun˜a, Campus da Zapateira s/n, 15071 A Corun˜a, Spain eDepartment of Marine Biochemistry, Marine Research Institute, CSIC, C/ Eduardo Cabello 6, 36208 Vigo, Spain Abstract High-resolution geochemical analyses obtained using an X-ray fluorescence (XRF) Core Scanner, as well as mineralogical data from the Lago Chungara´ sedimentary sequence in the northern Andean Chilean Altiplano (181S), provided a detailed reconstruction of the lacustrine sedimentary evolution during the last 14,000 cal. yr BP. The high-resolution analyses attained in this study allowed to distinguish abrupt periods, identify the complex structures of the early and mid-Holocene arid intervals and to compare their timing with Titicaca lake and Sajama ice records. Three main components in the lake sediments have been identified: (a) biogenic component, mainly from diatoms (b) volcanics (ash layers) from the nearby Parinacota Volcano and (c) endogenic carbonates. The correlation between volcanic input in Lago Chungara´ and the total particles deposited in the Nevado Sajama ice core suggests the Parinacota Volcano as the common source. The geochemical record of Lago Chungara´ indicates an increase in siliceous productivity during the early Holocene, lagging behind the rise in temperatures inferred from the Nevado Sajama ice core. The regional mid-Holocene aridity crisis can be characterized as a number of short events with calcite and aragonite precipitation in the offshore lake zones. r 2006 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction to any examination of rapid climate fluctuations, are scarce, with diverse proxy records showing numerous Recent research of past climate oscillations has found discrepancies (i.e. Grosjean, 2001). Detailed knowledge of that changes between climate modes during the Holocene the distribution and amplitude of abrupt climate changes in occurred within decades (Mayewski et al., 2004), a period tropical latitudes of the Andean Altiplano is still sparse and of time similar to more recent climate changes (Houghton the processes responsible for climate variability at different et al., 2001). In this context, scientific efforts over the last temporal and regional scales are barely understood. The few years have been directed towards understanding the suggested close link between higher lake levels in the timing and mechanisms of abrupt climate changes during Andean Altiplano and cold sea surface temperatures in the the last millennia. Despite the recent increase in the number Equatorial Atlantic (i.e., Heinrich events, Younger Dryas, of high-resolution paleoclimate records from low latitudes 8.2 kyr event or the Little Ice Age) indicated by the Titicaca (e.g. Hughen et al., 1996, 2004; Kuhlmann et al., 2004), the lake record (Baker et al., 2001a) requires additional records role of the tropics in abrupt Holocene climate changes from tropical South America to confirm this paleoclimate remains a matter of debate. Tropical South America teleconnection between the two hemispheres. exemplifies the complexity of Holocene climate reconstruc- The evolution of temporal and spatial moisture patterns tions, in which high-resolution terrestrial records, essential during the Holocene is one of the main controversies surrounding studies of South American paleoclimate. It ÃCorresponding author. Tel.: +34 976 716118; fax:+34 976 716019. has been generally accepted that the northern-central E-mail address: [email protected] (A. Moreno). Andes were a generally arid region from 7 to 4 kyr BP 1040-6182/$ - see front matter r 2006 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2006.10.020 ARTICLE IN PRESS A. Moreno et al. / Quaternary International 161 (2007) 4–21 5 as observed in lacustrine (Abbott et al., 1997; Baker et al., 2001a; Grosjean et al., 2003; Paduano et al., 2003; Tapia et al., 2003) and ice-core records (Thompson et al., 1998; Thompson et al., 2000). This hypothesis is also supported by archeological evidence (Nu´ n˜ ez et al., 2002). In addition to moisture reconstructions, a recent study of long-chain alkenones from Titicaca lake sediments also points to enhanced regional temperatures during the mid-Holocene (Theissen et al., 2005). However, other recent studies support a more complex spatial and temporal pattern, and even periods of increased humidity during the mid- Holocene (Holmgren et al., 2001; Latorre et al., 2003; Servant and Servant-Vildary, 2003). Paleoclimate sedimen- tary records possessing a robust and accurate chronologi- cal framework are therefore imperative to understanding both the regional significance and the timing of abrupt humidity changes detected during the mid-Holocene. The overall goal of this study was to document the regional pattern of climatic change for the last 14,000 cal. yr BP using a sedimentary record from Lago Chungara´ (Andean Altiplano, 181S). This paper reports a high-resolution geochemical record from the lake obtained by an X-ray fluorescence (XRF) core scanner together with other paleoenvironmental indicators (i.e. physical proper- ties, mineralogy, opal content and total organic carbon (TOC)). The resulting high-resolution analyses, in tandem with a multi-proxy approach, allowed us not only to infer the paleoclimate signal from the Lago Chungara´ record, but also to contribute to the identification, correlation and understanding of abrupt climate change during the Holocene in tropical regions of South America. 2. Location, climate and limnology of Lago Chungara´ 0 0 Lago Chungara´ (18115 S, 69110 W, 4520 m asl) is located Fig. 1. (a) Location of Lago Chungara´ and other paleoclimatic records on in the highest and westernmost fluvio-lacustrine basin in the Northern Chilean Altiplano. (b) Position of sediment cores in Lago the Andean Altiplano (Northern Chile, Fig. 1a). This lake Chungara´ . Isobaths and main inflows are indicated. sits in the central part of a small hydrologically closed subbasin at the northeastern edge of the Cenozoic Lauca jet stream as well as the intensification of the Bolivian high- Basin. The intense volcanic activity and, to a lesser extent, pressure system (Garreaud, 2001; Garreaud et al., 2003). the movement of synsedimentary faults are significant Average annual rainfall in the region is about 350 mm. A factors for sedimentation in the Chungara´ subbasin. The significant fraction of the inter-annual variability of Lago Chungara´ subbasin was formed after the collapse of summer precipitation is currently related to the El Nin˜ o the Parinacota Volcano (Fig. 1a), which produced a huge Southern Oscillation (ENSO) (Vuille, 1999). Thus, wet debris avalanche blocking the Paleo-Lauca River at about summers on the Andean Altiplano are associated with an 15–17 kyr BP (Wo¨ rner et al., 1988; Wo¨ rner et al., 2000; ENSO-related cooling of the tropical Pacific (La Nin˜ a Wo¨ rner et al., 2002). However, the age of this collapse is phase). controversial, and it has been estimated at 8 kyr by other Lago Chungara´ has a maximum water depth of 40 m, a authors (Clavero et al., 2002, 2004). The local vegetation is surface area of 22.5 km2 and a volume of about dominated by tussock-like grasses, shrubs, Polylepsis,a 426 Â 106 m3 (Risacher et al., 2003; Herrera et al., 2006). dwarf tree of the Rosaceae family, as well as extensive The main inflow is the Chungara´ River (300–460 l sÀ1) and soligenous peatlands (‘‘bofedales’’) (Schwalb et al., 1999; several springs on the western margin. Although there is no Earle et al., 2003). surface outlet, groundwater outflow was estimated as Lago Chungara´ is climatically located in the arid Central 0.2 m3 sÀ1 (Montgomery et al., 2003) and the water lost Andes. This region is dominated by tropical summer by potential evaporation measuring about 1230 mm yrÀ1 moisture stemming from the Amazon Basin, and is (Risacher et al., 2003). The lake is polymictic, meso to controlled by the southward migration of the subtropical eutrophic and contains 1.3 g lÀ1 total dissolved solids ARTICLE IN PRESS 6 A. Moreno et al. / Quaternary International 161 (2007) 4–21 (Mu¨ hlhauser et al., 1995). Water chemistry is of texture, color and sedimentary structures (Core 11, Fig. 2). Na–Mg–HCO3–SO4 type with an average pH of 9. At Smear slides were described using a Nikon polarizing present, oxic conditions extend to the lake bottom. Primary microscope to estimate the biogenic, clastic and endogenic productivity in the lake is mainly governed by diatoms and mineral content of the defined sedimentary facies. Sub- chlorophyceans. During four sampling periods from 1998 samples were taken every 5 cm for mineralogical, chemical to 1999, biomass values fluctuated from 0.34 to 8.74 mg and biological analyses. After a detailed lithological Chlorophyll a lÀ1 (Dorador et al., 2003). Oscillations in correlation of all cores (Fig. 3 and Sa´ ez et al., 2007), cores both, phytoplanktonic biomass and phytoplanktonic com- 10 and 11 were selected for paleoclimatic and paleoenvir- munity structure seem to be mainly due to changes in water onmental reconstructions. Both cores recorded almost the column temperature and salinity. entire sedimentary infill of the offshore zone, allowing reconstruction of a composite sequence. 3. Materials and methods Total carbon (TC) and total inorganic carbon (TIC) contents were determined by a UIC model 5011 CO2 In November 2002, 15 sediment cores (6.6 cm inner Coulometer, with TOC content then calculated.