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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.
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Holocene History of Río Tranquilo Glacier, Monte San Lorenzo (47°S), Central Patagonia
The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10 Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.
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- Award ID(s):
- 1804816
- PAR ID:
- 10310991
- Date Published:
- Journal Name:
- Frontiers in Earth Science
- Volume:
- 9
- ISSN:
- 2296-6463
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/feart.2021.813433
