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)

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 (similar to 21 ka 1313). In this study we present a new chronology based on cosmogenic He-3 (He-3(c)) dating of moraines on Cerro Tunupa, a volcano that is located in the centre of the now vanished Lake Tauca (19.9 degrees S, 67.6 degrees W). These new He-3(c) ages suggest that the Tunupa glaciers remained close to their maximum extent until 15 ka BP, synchronous with the Lake Tauca highstand (17-15 ka BP). Glacial retreat and the demise of Lake Tauca seem to have occurred rapidly and synchronously, within dating uncertainties, at similar to 15 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 similar to 6.5 degrees C cooler and average precipitation higher by a factor ranging between x1.6 and x3 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. (C) 2009 Elsevier Ltd. All rights reserved.