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Understanding Glacier Thinning and Retreating During the Last Glacial Maximum in Yosemite to Predict Contemporary Deglaciation
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  • Yueyi Che,
  • Alyssa Abbey,
  • David Shuster,
  • Greg Balco,
  • Greg Stock,
  • Kurt Cuffey
Yueyi Che
University of California, Berkeley

Corresponding Author:[email protected]

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Alyssa Abbey
California State University Long Beach
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David Shuster
University of California Berkeley
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Greg Balco
Berkeley Geochronology Center
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Greg Stock
Yosemite National Park
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Kurt Cuffey
University of California Berkeley
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We describe new cosmogenic Be-10 and C-14 exposure age dating on previously glaciated bedrock samples from Lyell Canyon as constraints to model the glacier’s rate and timing of thinning and retreat after the Last Glacial Maximum (LGM). Close analysis of deglaciation following the LGM (22-12 ka) can offer insight into how glacier retreat proceeds in a warming climate. The extent and age of the LGM glaciation in Yosemite National Park, California are relatively well-constrained. Our new exposure ages from Yosemite can quantify the change of the glaciation after the LGM. This is important because the rate and timing of glacier retreat after the LGM allows us to learn about the LGM-Holocene climate transition. We collected 16 granodiorite bedrock samples from the Lyell Canyon walls in three vertical transects: at the end, in the middle, and near the head of Lyell Canyon. Sample elevations range from 2781m to 3388m. The samples are being processed for cosmogenic Be-10 and C-14 concentrations (for the lower and higher elevations in the transects, respectively). Together with previously acquired Be-10 exposure ages from glacial polished bedrock and boulders at the canyon floor, our vertical transects will help to define the relationship between glacier retreat and thinning along the valley. The combination of different nuclide measurements has the potential to reveal whether the glacier melted rapidly or went through multiple thinning and thickening cycles. We created several simple forward models of cosmogenic Be-10 and C-14 exposure ages on the valley wall for different glacier thinning patterns: (i) rapid thinning, (ii) thinning and thickening cycles during the melting, (iii) thickening first, followed by thinning, and (iv) breaking an upper small cirque glacier from the main glacier during the thinning. After we have obtained all our data, we will compare the exposure age data to our modeled scenarios, as well as local paleoclimate records, to quantify the glacier’s geometry and mass balance during the climate warming period. Understanding the timing, rates, and patterns of LGM retreat and thinning constitute a useful test case that aids mountain glacier melting predictions and water budget planning under contemporary climate change in analogous environments.