Alaska-wide records of LGM advances
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laska-wide records of LGM advances
description
Alaska-wide records of LGM advances. 3 Questions to consider:. How can you recognize what valleys had LGM glaciers? What are the strengths and limitations of using cosmogenic exposure dating on moraines in Alaska? What can one do with a state-wide compilation of dated moraine records?. - PowerPoint PPT Presentation
Transcript of Alaska-wide records of LGM advances
Alaska-wide records of LGM advances
3 Questions to consider:
1. How can you recognize what valleys had LGM glaciers?
2. What are the strengths and limitations of using cosmogenicexposure dating on moraines in Alaska?
3. What can one do with a state-wide compilation of datedmoraine records?
The Alaska Range
Kaufman and Manley, 2004
AKR
21.9±0.9
19.2±0.8
18.2±0.7
19.3±1.0
55.4±1.4
47.9±1.7
44.2±1.8
51.4±1.6
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new data from Dortch, Owen
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Notable Alaska Range chronologies
North-Central Alaska Range
Modified from Hamilton (1982)
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30
• 10Be ages on penultimate moraines in two areas point to MIS 4/3 age.
• 10Be ages on LLGM moraines in two areas are ~20 ka.
• 10Be ages on late glacial moraine possibly YD in age.
The Brooks Range
Kaufman and Manley, 2004
BR
Hamilton, 2003
Hamilton, 1994
Age
(ka
)
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Modified from Hamilton (1982)
Central Brooks Range
20
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Notable Brooks Range chronologies
• Hamilton (2003) reports 14C ages that constrain late-glacial advance to ~15 to 13.1 ka
• Two moraines from penultimate advance younger than Old Crow Tephra (~140 ka)
• 10Be ages in NE BR agree with 14C chron.
Spatial Patterns
Reconstructed ELAs from across the state consistently show moisturesource in the west/southwest - North Pacific and Bering Sea
ELAs and moisture source
Brooks Range ELAs
Balascio et al., 2005
Spatial Patterns
Reconstructed ELAs from across the state consistently show moisturesource in the west/southwest - North Pacific and Bering Sea
Spatial pattern of timing of the MIS 2 advance
ELAs and moisture source
Enough information is at hand to conclusively show that the timing of MIS 2 max occurs at different ages in differentregions across the state
Kaufman and Manley, 2004
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22
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24 20
18
retreatfromMIS 2
terminalmoraine (ka)
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Summary
Main Points1. The maximum Late Pleistocene advance in AK post-dates the LIG
and pre-dates the global LGM, and seems to be 60-50 ka where dated.
2. MIS 2 pulse appears to be bimodal, ending either ~26 (in the north) or ~20 ka (elsewhere).
3. There is limited chronological control on late glacial moraines; could be YD in two places; late glacial moraines exist across AK.
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MIS 4
Main Points4. Several forcing factors for Alaskan climate:
- Emergence of the Bering land bridge
-N Pacific SST
-The location of the Aleutian Low
