Holocene Glacier Length Variations Along the American Cordillera from the 14C-10Be Chronometer
Abstract
The length of modern alpine glaciers in a long-term context and their size trends at the hemisphere scale over the Holocene are largely unresolved. While valuable, traditional approaches to Holocene glacier reconstruction typically provide snapshots in time, qualitative proxies that cannot be directly linked to glacier length, and intervals of expanded rather than contracted ice extent— the situation of most relevance to today.
We are applying the in situ 14C-10Be chronometer to recently exposed proglacial bedrock at approximately a dozen sites along the American Cordillera to reconstruct hemisphere-scale trends in Holocene glacier extent. 14C and 10Be accumulate in bedrock exposed to cosmic radiation, but nuclide production effectively ceases when the rock is shielded by ice cover. The 14C/10Be ratio then decreases due to the faster decay of 14C (t1/2 = 5.7 kyr) relative to 10Be (t1/2 = 1.4 Myr), which remains nearly constant on Holocene timescales. In addition, glacial erosion reduces the concentration of both nuclides. As a result, the Holocene history of ice extent relative to today can be constrained by measuring 14C and 10Be concentrations in bedrock samples taken along the current ice margin, which presumably have experienced the same exposure history but potentially different magnitudes of glacial erosion. We will present initial cosmogenic data for several glaciers in North and South America from this ongoing work, and will interpret the results with a Monte Carlo scheme that calculates cosmogenic nuclide concentrations expected for thousands of possible burial and exposure histories.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP51F1433G
- Keywords:
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- 1009 Geochemical modeling;
- GEOCHEMISTRY;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY;
- 4924 Geochemical tracers;
- PALEOCEANOGRAPHY;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY