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 (∼21 ka BP). In this study we present a new chronology based on cosmogenic 3He (3Hec) 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 3Hec 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 ∼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 ∼6.5 °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.
Bibliographical noteFunding Information:
Constructive comments by Wallace S. Broecker, Joerg M. Schaefer and Ano N. Ymous improved an earlier version of this manuscript. This work was mainly funded by the French INSU program “Relief de la Terre” and by the Caltech Tectonics Observatory. It is part of the Post Doc of P.-H. Blard. The authors thank the IRD (Institut de Recherche pour le Développement) of La Paz, Bolivia, which provided a precious technical and logistical assistance in the field. This is CRPG contribution #2017.