Timing and extent of late pleistocene glaciation in the arid Central Andes of Argentina and Chile (22°-41°S)

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 Nino 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 degrees and 22 degrees S suggest that glaciers advanced: i) prior to the global Last Glacial Maximum (gLGM) at similar to 40 ka in the mid (26 degrees-30 degrees S) and southern Central Andes (35 degrees-41 degrees 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 CO2 concentration and increasing temperature starting at similar to 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 Nina-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 39 degrees-41 degrees S, further north at 31 degrees S and in the northernmost Central Andes at 22 degrees S glacial remnants even point to precipitation driven glaciations older than similar to 115 ka and 260 ka.