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Deposits preserved on peaks in the southern Peruvian Andes are evidence for past glacial fluctuations and, therefore, serve as a record of both the timing and magnitude of past climate change. Moraines corresponding to the last major expansion of ice on Nevado Coropuna date to 20-25 ka, during the last glacial maximum. We reconstructed the snowline at Coropuna for this period using a combined geomorphic-numeric approach to provide a first-order estimate of the magnitude of late-Pleistocene climate change. Our reconstructions show that snowline was approximately 550-770 m lower during the last glacial maximum than during the late Holocene maximum, which ended in the 19(th) century, and similar to 750 m lower than today. While these values are similar to data from nearby Nevado Solimana, reconstructions from the neighbouring peak of Nevado Firura reveal a smaller snowline depression, suggesting the glacial response to climate forcing in the tropics is strongly influenced by non-climatic factors. These data constitute some of the first directly dated palaeo-snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical Andes was similar to late-Pleistocene events at higher latitudes. Copyright (c) 2011 John Wiley & Sons, Ltd. Funding for the fieldwork was generously provided by the Dan and Betty Churchill Foundation, the Geological Society of America Graduate Student Research Grant programme, the Sigma Xi Grants‐in‐aid‐of‐research programme and the Comer Science and Educational Foundation. peer-reviewed

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher-latitude regions, well-dated records from the Tropics are rare and the structure of late-glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic He-3 surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late-glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 +/- 0.7 ka (1 sigma). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru. Copyright (C) 2011 John Wiley & Sons, Ltd. peer-reviewed