1. Alaska-wide records of LGM advances

2. 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?

10. The Alaska Range
AKR
Kaufman and Manley, 2004

11. 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

12. new data from Dortch, Owen40 60 20 10

13. 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)

23. BR
The Brooks Range
Kaufman and Manley, 2004

24. Age (ka) ?
Hamilton, 1994
Hamilton, 2003

25. 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

36. 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

37. Brooks Range ELAs
Balascio et al., 2005

38. 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

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

40. Summary

41. Main Points
1. The maximum Late Pleistocene advance in AK post-dates the LIG
and pre-dates the global LGM, and
seems to be 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.

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