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?

The Alaska Range AKR Kaufman and Manley, 2004

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

new data from Dortch, Owen 40 60 20 10

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. 30 • 10Be ages on late glacial moraine possibly YD in age. Modified from Hamilton (1982)

BR The Brooks Range Kaufman and Manley, 2004

Age (ka) ? Hamilton, 1994 Hamilton, 2003

Notable Brooks Range chronologies Modified from Hamilton (1982) Central Brooks Range 20 30 • 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

retreat from MIS 2 terminal moraine (ka) 26 24 21 20 21 18 22 Kaufman and Manley, 2004

Summary

Main Points 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. MIS 4 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 4. Several forcing factors for Alaskan climate: - Emergence of the Bering land bridge The location of the Aleutian Low N Pacific SST