Timing and extent of late pleistocene glaciation in the arid central andes of Argentina and Chile (22°-41°s)

Abstract

The arid Central Andes are a key site to study changes in intensity and movement of the three main atmospheric circulation systems over South America: the South American Summer Monsoon (SASM), the Westerlies and the El Niño Southern Oscillation (ENSO). In this semi-arid to arid region glaciers are particularly sensitive to precipitation changes and thus the timing of past glaciation is strongly linked to changes in moisture supply. Surface exposure ages from study sites between 41° and 22°S suggest that glaciers advanced: i) prior to the global Last Glacial Maximum (gLGM) at ~40 ka in the mid (26°-30°S) and southern Central Andes (35°-41°S), ii) in phase with the gLGM in the northern and southern Central Andes and iii) during the late-glacial in the northern Central Andes. Deglaciation started synchronous with the global rise in atmospheric CO2concentration and increasing temperature starting at ~18 ka. The pre-gLGM glacial advances likely document enhanced precipitation related to the Southern Westerlies, which shifted further to the North at that time than previosuly assumed. During the gLGM glacial advances were favored by decreased temperatures in combination with increased humidity due to a southward shifted Intertropical Convergence Zone (ITCZ) and SASM. During the late-glacial a substantial increase in moisture can be explained by enhanced upper tropospheric easterlies as response to an intensified SASM and sustained La Niña-like conditions over the eastern equatorial Pacific that lead to glacial advances in the northern Central Andes and the lake level highstand Tauca (18-14 ka) on the Altiplano. In the southernmost Central Andes at 39º-41°S, further north at 31°S and in the northernmost Central Andes at 22°S glacial remnants even point to precipitation driven glaciations older than ~115 ka and 260 ka.