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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?.
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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?
The Alaska Range AKR Kaufman and Manley, 2004
21.9±0.9 47.9±1.7 18.2±0.7 55.4±1.4 19.2±0.8 44.2±1.8 51.4±1.6 19.3±1.0
10 40 20 60 new data from Dortch, Owen
Notable Alaska Range chronologies North-Central Alaska Range • 10Be ages on penultimate moraines in two areas point to MIS 4/3 age. 20 • 10Be ages on LLGM moraines in two areas are ~20 ka. • 10Be ages on late glacial moraine possibly YD in age. 30 Modified from Hamilton (1982)
The Brooks Range BR Kaufman and Manley, 2004
Age (ka) ? Hamilton, 1994 Hamilton, 2003
Notable Brooks Range chronologies Central Brooks Range 20 30 Modified from Hamilton (1982) • Two moraines from penultimate advance younger than Old Crow Tephra (~140 ka) • 10Be ages in NE BR agree with 14C chron. • Hamilton (2003) reports 14C ages that constrain late-glacial advance to ~15 to 13.1 ka
Spatial Patterns ELAs and moisture source Reconstructed ELAs from across the state consistently show moisture source in the west/southwest - North Pacific and Bering Sea
Brooks Range ELAs Balascio et al., 2005
Spatial Patterns ELAs and moisture source Reconstructed ELAs from across the state consistently show moisture source in the west/southwest - North Pacific and Bering Sea Spatial pattern of timing of the MIS 2 advance Enough information is at hand to conclusively show that the timing of MIS 2 max occurs at different ages in different regions across the state
26 22 21 24 20 18 21 retreat from MIS 2 terminal moraine (ka) Kaufman and Manley, 2004
Main Points MIS 4 1. 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.
Main Points • The location of • the Aleutian Low 4. Several forcing factors for Alaskan climate: - Emergence of the Bering land bridge • N Pacific SST