RECENT GLACIAL HISTORY AND PALEOCLIMATE OF THE PERUVIAN-BOLIVIAN ANDES

Radiocarbon dates of glacial deposits in the Peruvian-Bolivian Andes are used to place the observed phases of glaciation in a common chronological framework. The climatic conditions that may determine modern snowline are examined in order to understand the types of climatic forcing to which glaciers may have been sensitive in the past. Also considered are independent proxies of climatic change, including pollen sequences, lake-level history, and ice-core data. Late-Pleistocene glaciation in central Peru between 24 ka and 12 ka BP appears to have occurred during colder and perhaps drier conditions. In Bolivia a glacial maximum is dated to <27 ka BP and perhaps as late as ca. 16 ka BP. Because of the extreme height of snowline above the 0°C isotherm in Bolivia phases of glaciation must be correlated to not only colder conditions but also to a substantial increase in precipitation. During retreat from the last glacial maximum in Peru and Bolivia, between ca. 12 ka and 10 ka BP, there is evidence in many localities for a minor readvance of glaciers or a series of still stands. There is no evidence for early Holocene glaciation. Phases of late-Holocene glaciation in Peru that correspond in part to the Little Ice Age in the northern hemisphere appear to have been caused by a combination of colder and wetter conditions. An overall warming trend may be the cause for the retreat of many glaciers in the region since the mid-19th century. © 1990.