LATE-QUATERNARY GLACIER FLUCTUATIONS AND CLIMATE CHANGE AT NEVADO COROPUNA, SOUTHERN PERÚ

Determining the role of the tropics in global climate change remains a key problem in climatologic research with important implications for our understanding of abrupt climate change and for future climate prediction. Yet our ability to fully assess tropical behaviour during major climate events, such as the last glacial maximum (LGM) and the last glacial-interglacial transition, is limited both by a lack of conclusive palaeoclimate data and by poor spatial coverage of the tropical dataset. Here, we present glacial-geologic and preliminary surface-exposure age data from Nevado Coropuna (15.2ºS; 6400 m), south-western Perú, that help address this limitation. Our mapping and geomorphic investigations have revealed that glacial deposits corresponding to five separate episodes are well-preserved on both Coropuna and neighbouring Nevado Solimana. Initial cosomogenic-3He ages from moraines and drift limits on Coropuna suggest that the LGM in southern Perú terminated ~20-18 ka BP and, therefore, was broadly synchronous with the global LGM. Additional cosmogenic data show that a major readvance of Coropuna's glaciers occurred during the Late-glacial period, possibly in response to either the Younger Dryas or Antarctic Cold Reversal. Combined geomorphic and numeric ELA reconstructions show that, during the LGM, the ELA in southern Perú was more than 800 m lower than today. Although preliminary, our data strongly suggest that the pattern of Late-Quaternary climate change in this part of the southern tropics paralleled that of higher latitudes. In addition, we are addressing the urgent need for a directly calibrated production rate of cosmogenic isotopes in high-altitude/low-latitude sites such as the tropical Andes.