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The timing, structure and termination of the last southern mountain glaciation and its forcing remains unclear. Most studies have focused on the global Last Glacial Maximum (LGM; 26.5–19 ka) time period, which is just part of the extensive time-frame within the last glacial period, including Marine Isotope Stages 3 and 4. Understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change. Here, we present an extensive (n = 65) cosmogenic ¹⁰Be glacier chronology derived from moraine belts marking the pre-global LGM extent of the former Patagonian Ice Sheet in southernmost South America. Our results show the mountain ice sheet reached its maximum extent at 48.0 ± 1.8 ka during the local LGM, but attained just half this extent at 21.5 ± 1.8 ka during the global …