Late local glacial maximum in the Central Altiplano triggered by cold and locally-wet conditions during the paleolake Tauca episode (17–15 ka, Heinrich 1) P.-H. Blard a, b, * , J. Lave ´ b , K.A. Farley a , M. Fornari c, d , N. Jime ´ nez e , V. Ramirez e a Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA b Centre de Recherches Pe ´trographiques et Ge ´ochimiques, UPR 2300, CNRS, Nancy-Universite´, Vandœuvre-le `s-Nancy, France c Institut de Recherche pour le De´veloppement, France d Ge ´oazur, UMR 6526, CNRS, Universite´ de Nice, Nice, France e Universidad Mayor de San Andre ´s, La Paz, Bolivia article info Article history: Received 8 July 2009 Received in revised form 18 September 2009 Accepted 28 September 2009 abstract The timing and causes of the last deglaciation in the southern tropical Andes is poorly known. In the Central Altiplano, recent studies have focused on whether this tropical highland was deglaciated before, synchronously or after the global last glacial maximum (w21 ka BP). In this study we present a new chronology based on cosmogenic 3 He ( 3 He c ) dating of moraines on Cerro Tunupa, a volcano that is located in the centre of the now vanished Lake Tauca (19.9  S, 67.6  W). These new 3 He c ages suggest that the Tunupa glaciers remained close to their maximum extent until 15 ka BP, synchronous with the Lake Tauca highstand (17–15ka BP). Glacial retreat and the demise of Lake Tauca seem to have occurred rapidly and synchronously, within dating uncertainties, at w15 ka BP. We took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the Lake Tauca highstand. This new approach indicates that, during the Tauca highstand (17–15 ka BP), the centre of the Altiplano was characterized by temperature w6.5  C cooler and average precipitation higher by a factor ranging between 1.6 and 3 compared to the present. Cold and wet conditions thus persisted in a significant part of the southern tropical Andes during the Heinrich 1 event (17–15 ka BP). This study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The Tropics are recognized to play a major role in paleoclimatic cycles (Stocker et al., 2001) because this area may potentially generate forcing (i) at the global scale, e.g. through the tight link between tropical sea-surface temperature (SST) and atmospheric CO 2 and CH 4 concentrations (Lea, 2004), and (ii) at the regional scale, e.g. through the feedbacks between moisture transport and the thermohaline circulation (Leduc et al., 2007). However, our understanding of the exact mechanisms involved in these inter- actions is limited by the lack of precise chronologies in several key tropical areas (Hastenrath, 2009). This is particularly true for the highlands of the continental realm, where the past extents of mountain glaciers can be used to reconstruct with precision changes in temperature and precipitation (e.g. Hostetler and Clark, 2000). The Altiplano is a key area within this tropical puzzle: this high plateau is located at the interface between tropical and mid-latitude atmospheric circulation (Kull et al., 2008) and so is likely to have experienced substantial changes in precipitation and temperature during the last deglaciation (20–10 ka), and particu- larly during the 17.5–14.5 ka period termed ‘‘Mystery Interval’’ by (Denton et al., 2006). Although the presence of ancient mountain glaciers is reported in several places on the Altiplano (Smith et al., 2008; Zech et al., 2008), the spatial pattern and the timing of paleosnowline changes remain challenging issues (Rodbell et al., 2009). A discussion between Clark (2002) and Seltzer et al. (2002) focused on the relative timing between the global last glacial maximum (LGM, 21 ka) and the late Pleistocene glaciation in the tropical Andes. Cosmogenic 10 Be ( 10 Be c ) ages from moraines located in the northern part of the Altiplano suggest that the last glacial maximum occurred as early as w25 ka BP in the Tropical Andes * Corresponding author. Centre de Recherches Pe ´trographiques et Ge ´ ochimiques, UPR 2300, CNRS, Nancy-Universite ´ , Vandœuvre-le `s-Nancy, France. Tel.: þ33 3 83 59 42 23. E-mail address: blard@crpg.cnrs-nancy.fr (P.-H. Blard). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev ARTICLE IN PRESS 0277-3791/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2009.09.025 Quaternary Science Reviews xxx (2009) 1–14 Please cite this article in press as: Blard, P.-H., et al., Late local glacial maximum in the Central Altiplano triggered by cold and locally-wet..., Quaternary Science Reviews (2009), doi:10.1016/j.quascirev.2009.09.025