Why are the Great Alaskan Tidewater Glaciers Advancing During the MWP

- Controls on Tidewaters

- Relevance to SLR

- The chronology of advance and Medieval Climate along GOA

- Possible reasons

GSA - Houston 2008

Acknowledgements: The College of Wooster, NSF, NPS, NGS, Keck Geology Consortium, USGS and INSTAAR for the great photos.

Greg Wiles, Dan Lawson, Tom Lowell, Dave Barclay

Pfeffer, 2007

Wrangell/ St. Elias Mountains

Kenai Mountains

ChugachMountains

50 km

Wrangell-St. Elias

Gulf of Alaska

Locations - Southern Alaska

Kenai

Peninsula

Alaska

Why is Sea Level Rising? - the top 3 reasons

1

2*

3

IPCC - AR4

1961-2003

1993-2003

Meier et al., 2007

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Most of the Ice from Small Glaciers is in Alaska

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Columbia Bay (T. Pfeffer)(Pfeffer et al., 2008)

Northwestern Glacier - Kenai Fjords National Park

McCarty

Northwestern

McCarty

Columbia Glacier has undergone 15 km of retreat since ~1982.

Field (1941) Molnia (2004)

Glacier Bay National Park and Preserve - Muir Glacier

Tidewater Glacier Cycle (Post, 1975)

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= sediment

Controls on Calving Glacier

• Climate - summer temperature/ winter precipitation

• Fiord geometry

• Water depth

• Sediment supply to glacier snout

Anderson 2006

30 km left

350 m = water depth

trimline

Calving front

icebergs

Columbia

Dendrochronology and Dendroclimatology

Forest Glacial History

ForestResponse

Columbia Bay - Kill Site

AD 1770

AD 1810

500 750 1000 1250 1500 1750 2000

Columbia Glacier Calendar Dates

Year AD

N = 430

Crossdated logs and Land-terminating record

MWP

Tree Ring Datesalong Columbia Bay

~1000 year advance~10s retreat

1020

1400

1810

1750

Austin was right

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Glacier BayNational Parkand Preserve

Greatest upliftin the world

~1cm of the 20 rise is from GB

Multiple advance andretreat duringthe Holocene

AD 850

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Multiproxy Comparisons

Glaciers = Summer Temperature 800 1000 1200 1400 1600 1800 2000

mean RW (mm)

0.5

1.0

1.5

2.0

Calendar Years

800 1000 1200 1400 1600 1800 2000

No. of series0

100

200

300

400

Sub-fossilLiving

Coastal Alaska RCS chronology

?

TR Indices

MWPLIA

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Structure of the Warming

Decadal variabilityIs strong

Sorting Out Climate and DynamicControls: Climate Variability

• Long-term - 10s-100s thousands of years • 1,000 years

• 100 years

• Pacific Decadal Variability (PDV)

Columbia Glacier and

Summer Temperature

800 1000 1200 1400 1600 1800 2000

mean RW (mm)

0.5

1.0

1.5

2.0

Calendar Years

800 1000 1200 1400 1600 1800 2000

No. of series0

100

200

300

400

Sub-fossilLiving

Coastal Alaska RCS chronology

advance

pause at

midfiord?

advanceadvance

Tidewater Glacier Cycle (Post, 1975)

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Tidewater Glaciers GSA Houston 2008

Alaska tidewater glaciers continue to lose mass and flux to the sea

During the MWP many were advancing - forced by tributary valleysediment contributions along with increased precipitation and decadal variability

Sorting out the dynamic and climatic controls over century to millennia is ongoing but it may be related to precipitation as it affects sediment flux

Pfeffer - Columbia Bay