10Be chronology of the Last Glacial Maximum and Termination in the Andes of central Chile: The record of the Universidad Glacier (34° S)

Abstract

Reconstructing mid-latitude glacier variations is a prerequisite for unveiling the interhemispheric climate linkages and atmospheric-ocean forcings that triggered those changes during the last glacial cycle. Nonetheless, the timing, magnitude, and structure of glacier fluctuations in the southern mid-latitudes remain incomplete. Here, we present a new ¹⁰Be chronology of the Universidad Glacier in the Andes of central Chile (34° S, 70° W; ∼2500 m a.s.l.) based on 21 cosmogenic-exposure ages of boulders on discrete moraine ridges defining former ice margins. Our findings include the mapping and dating of three moraines, UNI I, UNI II, and UNI III, located ∼20 km, 15 km, and 10 km down-valley from the present-day glacier front, respectively. The ¹⁰Be exposure ages of the UNI I moraine range from 135.9 ± 7.1 to 51.4 ± 2.7 ka (n = 3). The UNI II moraine gave a mean age of 18.0 ± 0.9 (n = 15) and the UNI III moraine yielded a mean age of 13.9 ± 0.8 ka (n = 3). The UNI I moraine implies the largest ice extent during a pre-Last Glacial Maximum (pre-LGM) period, including the penultimate glaciation. The UNI II is a moraine complex that represents cold and humid conditions in central Chile at the end of the LGM, which we attribute to the northward-shift of the Southern Westerly Winds (SWW). The UNI III moraine represents a return to glacial conditions interrupting the Termination, evidencing both a double-step deglacial trend observed through the southern middle and high latitudes at the end of the last ice age. The Andes at this subtropical latitude record a global signal of glacial and climate change.