The glacier-climate history of Cordillera Paraiacaca and Cordillera Huaytapallana, Central Peruvian Andes, From the Late Pleistocene to Holocene.

Deciphering the global and local drivers of glacial retreat in the tropical Andes in the Late Quaternary is key to understanding how future climate scenarios will affect these glaciers. In Peru, glaciers have high socioeconomic and cultural value, supplying drinking water, hydroelectric power and irrigation. Pariacacá and Huaytapallana mountain ranges (~11.5 ºS), provide meltwater to Lima and Huancayo. Glaciers in Pariacacá, in the western Andes, and Huaytapallana, in the eastern Andes, have experienced a 55% and 56% shrinkage in surface since the 1970s, respectively. No chronologies, however, exist for their extensive moraine sequences which provide clues to the dynamics under various climate forcing scenarios. These could help put present-day and future climate scenarios into context of contemporary change and be used as a test for models aiming to project the response of mountain glaciers to ongoing climate change. Using Terrestrial Cosmogenic surface exposure dating, this study provides the first glacial geochronology for these mountain ranges based on 32 10Be exposure ages of eight moraines. The Peruvian climate and glacial dynamics have been linked to variations in sea surface temperatures, the displacement of Intertropical Convergence Zone, and intensity of the South American Summer Monsoon. The climate is also modulated by the Andean Mountain chain, which acts as a topographical barrier causing a rain shadow on its western flank. This barrier affects the relative influence of these factors on the different sides of the Andes. This study aims to help constrain the ocean and atmospheric controls on past glacier mass balance in Peru, how the controls differed between the Eastern and Western Andes and how they have developed over the late Quaternary. Initial results from Pariacacá indicate a local glacial maximum at 32.6 ± 3ka, around 10kyrs earlier than the global LGM. Following this early glacial maximum, ice appears to have continuously retreated until the Older Dryas. A lateral moraine, dated to 15.9± 0.8ka suggests glacier stabilisation or advancement, under wetter conditions during Heinrich Stadial 1 as the Northern hemisphere cooled causing a southern displacement of the ITCZ. This indicates linkages between glacier retreat in the western Andes and Atlantic SSTs in the past. Following the Older Dryas stillstand the glacier retreated as the climate warmed and dried into the Holocene. A cluster of moraines dated to the Early Holocene (11.4 ± 0.6ka) further adds to the growing evidence that the overall warming trend was interrupted by short intervals of either colder or wetter conditions. Similar early Holocene stillstands are recorded in Huaytapallana at 11.4 ± 0.6ka and 10.9 ± 0.6ka. Both mountain ranges show geomorphological evidence of a Little Ice Age stillstand or advance. At Huaytapallana, initial data suggests this occurred  176 ± 13 years before 2022 during colder and wetter conditions.  Analysis of the exposure ages in comparison to palaeoclimate, along with palaeoglacier and palaeoclimate reconstructions will be presented.