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

40

60

new data from Dortch, Owen

20

10

Notable Alaska Range chronologies

North-Central Alaska Range

Modified from Hamilton (1982)

20

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

)

?

Modified from Hamilton (1982)

Central Brooks Range

20

30

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

26

22

21

24 20

18

retreatfromMIS 2

terminalmoraine (ka)

21

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.

0

10

20

30

40

50

60

70

80

90

100

0

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