Temperature reduction and local last glaciation maximum (LLGM) : the example of the east-Andean Cordillera around Cochabamba, Bolivia (17°S)

This study presents results from a glacier-climate model that reconstructed glacio-climatological conditions during the last local glaciation maximum (LLGM) in the Cordillera to the north of Cochabamba (17 ° 15'S, 66 ° 15'W), Bolivia. Results emphasize the temperature-sensitivity of glaciers on the eastern slope of the Cordillera Oriental. Maximum glacier advances appear to have been caused by a massive cooling of about 6.5 ° C while annual preeipitation was about 300 mm higher than today (850 mm/yr). Modeling results indicate maximum glacial advances during cold phases such as MIS 2 (25–18 kyr B.P.) and minor advances during late glacial cool events (12–10 kyr B.P.). This chronology is supported by exposure age dating results. Further evidence may be found in the low AAR-values (accumulation area ratio) which indicate low mass balance gradients and therefore cold climate conditions. Modeled basal shear stresses smaller than 1 bar exelude extremely «cold-dry» or «warm-wet» conditions. The spatial pattern of regional paleo-ELA's (equilibrium line altitude). with higher ELAs in the western part of the study area, reflects a strong east-west gradient in paleoprecipitation. Easterly summer preeipitation is suggested to be the reason for this phenomenon. These results are in agreement with other studies of the east-Andean slope, indicating temperature as the driving factor for maximum glacier advances in northwestern Argentina.