7 field seasons and 250 cosmogenic exposure ages:Laurentide Ice Sheet history and dynamics

The Clyde River project, on northeastern Baffin Island

4 Questions to consider:

1. Why can’t blockfields be used as evidence for LGM refugia?

2. Recall that we’re presently in the “Goldilocks Paradigm.” Howis the Goldilocks model incorrect?

3. What are weathering zones really telling us?

4. What is potentially wrong with a story that is based on only a fewcosmogenic exposure ages?

10 km NClyde Foreland

Differentially-weathered fiord landscapes

Future work . . .

Extent of “fresh” zone indicates extent of LGM ice

Weathered uplands are covered, but not eroded, during the LGM

Tor: ≥67.5±7.2 ka

Boulder: 17.5±1.9 ka

Tor:≥64.1±2.2 (Be)≥61.4 ± 2.7 (Al)

Boulder:10.2±1.1

Cobble:11.6±0.9 (Be)14.8±1.7 (Al)

Future work . . .

Future work . . .

Updated from Briner et al., 2003,QSR

Locations of “LGM” erratics

380-430 m

410-610 m520-580 m620-690 m

? ??

?

Cold-based

Cold-based

warm-based

Shearzone Shear

zone

Ice Stream

Cold-based

Cold-based

warm-based

Shearzone Shear

zone

Ice Stream

South

North

10 km N

South North

glacially scoured

N S

no evidence of glacial erosion

glacially scoured

N S

no evidence of glacial erosion

some evidence of glacial modification

glacially scoured

N S

28.3+0.7 ka 32.5+1.1 ka

10.2+0.5 ka34.2+0.9 ka

9.5+0.7 ka23.3+0.7 ka

9.5+0.3 ka23.7+1.0 ka

11.4+0.5 ka11.6+0.3 ka80.0+3.4 ka

9.4+0.4 ka

22.0+0.7 ka

Cosmogenic Exposure ages: Bedrock and Erratics

28.3+0.7 ka 32.5+1.1 ka

10.2+0.5 ka34.2+0.9 ka

9.5+0.7 ka23.3+0.7 ka

9.5+0.3 ka23.7+1.0 ka

11.4+0.5 ka11.6+0.3 ka80.0+3.4 ka

9.4+0.4 ka

22.0+0.7 ka

erosive ice (>2 m of erosion)

erosive ice (<2 m of erosion)some glacial modification of upland bedrock

highest areas: no observable glacial modification

Clarke et al., in prep.

Future work . . .

Future work . . .

Future work . . .

Future work . . .

What we’ve learned:

?? ?

1. LGM ice at shelf break2. Uplands covered by cold-based ice

3. WZs mark of basal thermal regimes

4. Ice streams occupied fiords

weatheredfresh

10 km N

5.5±0.3

5.1±0.34.0±0.3

3.9±0.3

50.0±1.230.1±0.755.8±1.3

5.5±0.3

5.1±0.34.0±0.3

3.9±0.3

50.0±1.230.1±0.755.8±1.3

Al/Be burial age:~430 ka

Byrd Glacier, Antarctica

LANDSAT-1 image

Lambert Glacier: an Antarctic ICE STREAM

JPL - RADARSAT AMP

ice-sheet scalepatterns in basal thermal regime…

JPL - RADARSAT AMP

4 Questions to consider:

1. Why can’t blockfields be used as evidence for LGM refugia?

2. Recall that we’re presently in the “Goldilocks Paradigm.” Howis the Goldilocks model incorrect?

3. What are weathering zones really telling us?

4. What is potentially wrong with a story that is based on only a fewcosmogenic exposure ages?

2D numerical glacier model run in MatLab

Bob Anderson and Mark Kessler (University of Colorado)

Published:Kessler et al. 2006

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Erosion is deepest as it crosses the crest.Erosion accelerates through time

X-section of a typical Baffin Island Fjord

> 2 km

100 km

Bob Anderson, Mark Kessler

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.