Post on 16-Dec-2015
transcript
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
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)
Controls on Calving Glacier
• Climate - summer temperature/ winter precipitation
• Fiord geometry
• Water depth
• Sediment supply to glacier snout
Anderson 2006
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
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 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