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Understanding alpine glacier extent during past climate variability is instructive for determining the glacier response to future climate change. Villarrica volcano is a late Pleistocene stratovolcano located in Chile's Southern Volcanic Zone that was covered by the Patagonian Ice Sheet during the last glacial period, and still retains small remnant glaciers today. Moraines preserved several kilometers from the summit on different flanks of the volcano record a history of expanded glacier lengths during the Holocene. However, the precise ages of these moraines are unknown, and the Holocene glacial history of Villarrica remains poorly constrained, limiting our understanding of how glaciers in this region responded to Holocene climate change. To constrain the timing of these moraines, we analyzed cosmogenic 3He in olivine from 25 basaltic andesite moraine boulders for cosmogenic surface exposure dating. Our new chronology reveals multiple late Holocene glacier advances from different flanks of the volcano, with the glaciers culminating and abandoning their moraines during the early Neoglacial period at ∼3355 ± 190 a and ∼1735 ± 215 a, and during the last millennium spanning the Little Ice Age period at ∼720 ± 225 a, ∼370 ± 75 a, and in the last ∼200 years. Our analysis of Holocene climate proxies from south-central Chile indicates that the early Neoglacial advances and subsequent retreat likely reflect increased effective moisture delivered by intensified Southern Westerly Winds and associated shifts in their latitudinal position. In contrast, we interpret the last millennium glacier advances as primarily driven by reduced summer ablation linked to regional cooling, followed by glacier retreat due to increased temperatures. Our chronology and closely spaced moraine positions suggest that glacier retreat on Villarrica, and possibly the broader Southern Volcanic Zone, has been gradual during the late Holocene and interrupted by short-lived advances driven by varying changes in temperature and moisture. 

Tropical glaciers have retreated over recent decades, but whether the magnitude of this retreat exceeds the bounds of Holocene fluctuations is unclear. We measured cosmogenic beryllium-10 and carbon-14 concentrations in recently exposed bedrock at the margin of four glaciers spanning the tropical Andes to reconstruct their past extents relative to today. Nuclide concentrations are near zero in almost all samples, suggesting that these locations were never exposed during the Holocene. Our data imply that many glaciers in the tropics are probably now smaller than they have been in at least 11,700 years, making the tropics the first large region where this milestone has been documented. 

Abstract. Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Evidence from the southern mid-latitudes indicates that local glacial maxima preceded the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital forcings. To shed light on these processes, we investigated the glacial landforms shaped and deposited by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet, in southern Argentina. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We report that the Lago Argentino glacier lobe reached more extensive limits prior to the global LGM, advancing during the middle to late Pleistocene between 243–132 ka and during Marine Isotope Stage 3 (MIS 3), culminating at 44.5 ± 8.0 and at 36.6 ± 1.0 ka. Our results indicate that the most extensive advance of the last glacial cycle occurred during MIS 3, and we hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a latitudinal migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in modulating ice mass changes in the southern mid-latitudes. 

Abstract. There is unambiguous evidence that glaciers have retreated from their 19th century positions, but it is less clear how far glaciers have retreated relative to their long-term Holocene fluctuations. Glaciers in western North America are thought to have advanced from minimum positions in the Early Holocene to maximum positions in the Late Holocene. We assess when four North American glaciers, located between 38–60∘ N, were larger or smaller than their modern (2018–2020 CE) positions during the Holocene. We measured 26 paired cosmogenic in situ 14C and 10Be concentrations in recently exposed proglacial bedrock and applied a Monte Carlo forward model to reconstruct plausible bedrock exposure–burial histories. We find that these glaciers advanced past their modern positions thousands of years apart in the Holocene: a glacier in the Juneau Icefield (BC, Canada) at ∼2 ka, Kokanee Glacier (BC, Canada) at ∼6 ka, and Mammoth Glacier (WY, USA) at ∼1 ka; the fourth glacier, Conness Glacier (CA, USA), was likely larger than its modern position for the duration of the Holocene until present. The disparate Holocene exposure–burial histories are at odds with expectations of similar glacier histories given the presumed shared climate forcings of decreasing Northern Hemisphere summer insolation through the Holocene followed by global greenhouse gas forcing in the industrial era. We hypothesize that the range in histories is the result of unequal amounts of modern retreat relative to each glacier's Holocene maximum position, rather than asynchronous Holocene advance histories. We explore the influence of glacier hypsometry and response time on glacier retreat in the industrial era as a potential cause of the non-uniform burial durations. We also report mean abrasion rates at three of the four glaciers: Juneau Icefield Glacier (0.3±0.3 mm yr−1), Kokanee Glacier (0.04±0.03 mm yr−1), and Mammoth Glacier (0.2±0.2 mm yr−1).