Transcript History of the Greenland Ice Sheet: Paleoclimatic Insights

History of the Greenland Ice Sheet:
Paleoclimatic Insights
Richard B. Alley, J.T. Andrews, J. Brigham-Grette, G. K. C. Clarke, K
.M. Cuffey, J.J. Fitzpatrick, S. Funder, S. J. Marshall, G. H. Miller, J.
X. Mitrovica, D. R. Muhs, B. L. Otto-Bliesner, L. Polyak, J. W. C.
White
Mary G. Thibault
Undergraduate
Atmospheric Science and
Anthropology
Flight Plan
 Introduction
 Paper
 Summary
 Questions
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The Greenland Ice Sheet
Overview
 Dimensions
 Area ~ 1.7 million km2
 Average thickness ~ 1600 m
 Volume ~ 2.9 million km3
 Geology
 Some bedrock depressed below sea level
 Rests on bedrock above sea level
 Composition
 Old snow squeezed under bulk of new snow
The Greenland Ice Sheet
Overview
 Primary Mass Loss
Contributors
 Low-elevation melting
 Calving icebergs
 Recent Trends
 Increasing temperatures
 Greater snowfall
 More runoff from meltwater
 Mass balance losses
intensifying
Intergovernmental Panel
on Climate Change (IPCC),
2007
 Mass Balance
 1961-2003
 +25 to -60 Gt
 (-0.07 – 0.17 mm SLE)
 1993-2003
 -50 to -100 Gt
 (0.14-0.28 mm SLE)
 2005
 Even worse
The Greenland Ice Sheet
Ice Sheet Behavior
Internal Deformation, Meltwater, Friction, and Ice Shelves
The Greenland Ice Sheet
Ice Sheet Behavior
 Ice Flow Models
 Processes not included
 As a result, projections are not accurate
 IPCC (2007) on sea level projections
 Do not take “…future rapid dynamical changes in ice flow” into
account
 No upper bound for rising sea level
The Greenland Ice Sheet
Estimates of Ice Sheet Mass Balance over time
Merged South
and West
Greenland
Temperature
Record
Note:
-360 Gt/a = 1mm SL rise
The Greenland Ice Sheet
Ice Sheet Behavior
 If Ice Sheet margins are fixed:
 Center of the ice sheet is not very sensitive to forcings
 Accumulation increases ice thickness and increases slope on the
ice sheet
 Consequently, ice discharge increases
 If Ice Sheet margins change:
 Slope will increase or decrease which affects
flow rate
 Margins can experience effects quickly
 Central regions experience effects slowly
The Greenland Ice Sheet
Ice Sheet Behavior
 Deformation is faster in warmer ice
 In inland areas deformation
 Is slowed by cooling
 Causes ice to thicken
 May steepen ice sheet to increase ice flux
 Deep ice may not feel effects
for millennia
 Penetration time
 Temperature is not stationary
 Surface melt
.
How do we address all this uncertainty?
Paleoclimatology
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 Span: less than 15 ka
 Provide data for:
1. Flux and Ice-Rafted
Debris (IRD)
2. Glacial deposition on
trough-mouth fans
3. Stable-Isotopic and Biotic
Data
4. Geophysical data
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 More terrestrial indicators
 More discontinuous
 Land: Net Erosion
 Ocean: Net Depositon
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 Moraines
 Striated Surfaces
 Boulders
 Landform Appearance
 Glacier elevation
 Limits of glaciation
 Glacier Extent
 Proxy for temperature
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 Lake Sediments
 Continuous record
 Detailed record
 Isotopic Composition
 Micro and Macro fossils
 Shell type
 Climate data
 temperature
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 Records a two-fold history
 Glacial-Isostatic
adjustment
 Ocean Volume
High Water Marks
 Corals
 Directly dated three ways
 500,000 year span
Paleoclimatic Indicators
Best records are found on tropical and sub-tropical
low-wave energy carbonate coasts.
Paleoclimatic Indicators
High-wave-energy rocky coasts do not produce
as good of a record.
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores
 GPS
 Satellites
 Tide Gauges
 Earth’s Rotation
Paleoclimatic Indicators
Marine
Terrestrial
 Geomorphic
 Biological
 Glacial Isostatic
Adjustment and
Sea Level
 Far Field Sea Level
 Geodetic
 Ice Cores

18O:16O
ratio
 Temperature
 Precipitation
 Very Reliable
 Trapped Gases
 temperature
 Layer Thickness
 Accumulation rates
 Age
 Elevation history
How were these Paleoclimatic Indicators
Used in the Context of this Paper?
History of the Greenland Ice Sheet
Earth has experienced periods of great warming in the past.
History of the Greenland Ice Sheet
Interglacial periods mean higher sea levels
 MIS 11 (~ 400,000 ya)
 Higher sea levels than now
 Marine deposit from Alaska
 Oxygen Isotope and Faunal data
 Long
 Orbital forcing
 Comparable to Modern Temp.
 Within 1-2 oC
Indicates that Greenland Ice Sheet
disappeared completely!
History of the Greenland Ice Sheet
 MIS 9 (303-331 ka)
 Poorly constrained
 Conflicting Evidence
 Corals in Barbados
 Fringing Reefs on Henderson
Island
 Higher Sea Level
 Coral on Fossil Reef at Florida
Bay, Pleasant Point
 Close but not higher Sea
Level
 Sea Level not much higher
than today
 MIS 7 (190-241 ka)
 Reef and Terrace Records
 Marine Deposits of Coral in
Bermuda
 Sea Level about the same
as today
Photo: Gary Varvel
History of the Greenland Ice Sheet
 MIS 6 ( ~ 130-188 ka)
 MIS 5 ( ~ 74-130 ka)
 Most extensive Ice in
 Sea water moved inland
Greenland (probably)
 Evidence
 Glacial deposits in East
Greenland
 No Paleoclimatic ice sheet
reconstructions are
available
During MIS 6 – MIS 5
transition
 Marine deposits and glacial
deposits are preserved
 Higher temperatures in
Greenland than far-field
SST’s

Greenland Does Not Have A Continuous
Climate Record
History of the Greenland Ice Sheet
 MIS 5e (123 ka)
 Sea Level High Stand
 Coral and Reef data




W. Australia ~ 4 m
Bahamas ~ 5 m
Bermuda ~ 2-3 m
Florida Keys ~3-5 m (largest estimate)
 Local SL Average: 4-5 m higher than today
Fig. 5. Photographs of last interglacial (MIS5e) reef and
corals on Key Largo, Florida,their elevations,probable
water depths,and estimated paleo-sea level. Photographs
by D. R. Muhs.
Sea Level Estimates
History of the Greenland Ice Sheet
 However, the previous sea level estimations did not take
Glacial-Isostatic Adjustment into consideration.
 Bayesian Statistical Approach
 Accounts for scant and noisy data
 Derived local and globally averaged sea level (GSL) covariance
 Results for MIS 5e
 GSL exceeded
 6.6 m (95%)
 8.0 m (67%)
 9.4 m (33%)
Conditions in Greenland
 MIS 5e Temperatures
 Terrestrial Data (CAPE
2006)
 Peak: ~ 130 ka
 Climate Simulations
 Summer Sunshine
 Predicted maxima: 4-5 oC
 For NW, E and Marine
 Summer (higher than
recent)
 NW Greenland: ~ 4 oC
 E Greenland: ~ 5 oC
 Marine: ~ 2-3 oC
parts of Greenland
 ~3 oC
 For everywhere else
Conditions in Greenland
 As the world entered MIS 5e, Greenland began undergoing
deglaciation.
 Attributed to climate forcing
 Resulted from combination of Greenland deglaciation and
far-field land ice
Ice Sheet Changes
 MIS 5e Ice Sheet was smaller
 By how much?
 Uncertain because of lack of continuous Paleoclimatic data
 Unknown Key Constraints
 Temperature
 Precipitation
 Ice flow factors
 Many Theories
Conditions in Greenland
 Basic Theory is from Marshall and Cuffey (2000)
 Approach
 Used isotope ratios as constraints
o Depend on elevation and temperature
 Generated climate and ice-sheet histories
 Problems
 Depended on isotopic sensitivity parameter
 Past accumulation rates estimated
 Large uncertainties
 Ice flow was not considered
 Model produced smaller than observed scenarios
 Driven by only one record
Conditions in Greenland
 Another theory was developed by Otto-Bliesner et al (2006)
 New Approach
 Coupled ocean-atmosphere climate model
 Tested output against Paleoclimate data from around Greenland Ice
Sheet
 Did not have to use a sensitivity parameter for relating temperature to
isotopic composition
 Did not have to assume snow accumulation and temperature
 Considers Milankovich changes in radiation insolation as a primary
forcing
Modeled Greenland Ice Sheet
Configurations
Conditions in Greenland
 Results
 Produced Reconstructions that corresponded to Greenland and Arctic
data
 Cuffey and Marshall found MIS 5e to be
 snowy and very warm
 or a more modest estimate of it being warmer with less snowfall.
 Otto-Bliesner et al. favors the latter with the moderate change in
temperature.
 Indicates smaller rise in Sea Level than the first model
 Best estimate of MIS 5e Conditions
 Sea Level : 3-4 m
 Temperature: 3 oC – 4 oC
Climate Forcing
 Reconstructions from periods more recent than MIS 5e have
better confidence.
 Ice core records are especially helpful
 Near-field marine records are not as robust
 Rarely span more than 130,000 years
 Core HU90-013
 18O isotope change indicates cooling after MIS 5e
Greenland Cores
Climate Forcing




The Big Picture
Cooling from MIS 52 to MIS 2 (123 ka)
Warming Mid-Holocene/MIS 1 (millennia)
Cooling in Little Ice Age (centuries )
Warming
Greenland Cores
Near-Surface Plankton Oxygen-18 Isotopes
Renland Ice Cap
Greenland Cores
Oxygen 18 Isotope Cores
NW Labrador Sea
Greenland Cores
Oxygen 18 Isotope Cores
Davis Strait
Climate Forcing
Ice Isotope Records
Greenland
Byrd Station,
Antarctica
Ice Sheet Changes
 Greenland Ice Sheet
 Expanding when cooling
 Retreating when warming
 Cooling led to more ice volume
 Core total gas content
 Ice flow variables
 Glacial Margins
 Retreat means thinner central regions
 Advance means thicker central regions
Ice Sheet Changes
Uncertainties
 Ice extent and advance on Continental Shelf
 Rates and Times of Responses to short-lived climate changes
Since the Last Glacial Maximum
 Coldest conditions occurred 24,000 years ago
 Heinrich Event H2
 Since then, temperatures have fluctuated
 Earth’s orbit
 Expanded wintertime sea ice
Variations in Magnetic Susceptibility and
Oxygen 18 Isotopes
Present
Last Glacial
Maximum
Ice Rafted Debris Inputs
Conclusion:
The Greenland Ice Sheet has been changed significantly over
many past climatic eras.
Paleoclimatic Data Indicates:
 Temperature
 Cooling
Ice Sheet grows
 Warming
Ice Sheet shrinks
 Large Warming
Ice Sheet loss
 Control applies for current as well as higher past temperatures
 Sea Level
 Rising
Floats Margins of Ice Sheet
 Floating Margins
Forces Ice to Retreat
Increases in Both Temperature and Sea Level
Cause Volumetric
Reduction of the Ice Sheet.
Conclusion:
What forcings are most important?
 Snow does NOT increase ice sheet extent
 Greater snowfall means less ice
 Is NOT the primary forcing
 Sea Level change does NOT dominate Temperature forcing
 In recent millennia, fluctuations in ice sheet margins fit pattern of
Temperature forcing
 Expectations of Sea Level change forcing does not fit pattern
 Is NOT the primary forcing
Temperature is the dominant forcing in both the
short-term and the long-term.
Temperature vs. Volume
Conclusions
 They aren’t exactly ecstatic…
 Greenland Ice Sheet will shrink because of warming
 Even a few degrees will tip it over the edge
 Problems: We don’t know anything!
 Specific numerical constraints
 Established error bounds
 Rate of ice sheet loss
More Data Reconnaissance and Analyses
are Needed.
My Opinion
 A major problem with the data these scientists used was that
it was spotty and often inconsistent with other concurrent
areas of Paleoclimatic indicators.
 Need to improve data gathering techniques
 Need more people to become involved in field for data
analysis
Thank you very much!
Questions?
References
 http://www.cartoonstock.com/cartoonview.asp?catref=gra061031
 http://www.indystar.com/story/opinion/columnists/varvel/2014/01/03/cartoonist-
gary-varvel-climate-change-scientists-on-ice/4311735/
 http://earthsky.org/earth/greenland-glacier-melt-increases-mercury-discharge
 http://www.picgifs.com/clip-art/bugs-bunny/clip-art-bugs-bunny-625373-678516/
 http://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/
 http://www.sootoday.com/content/news/details.asp?c=86709
 http://research.bpcrc.osu.edu/Icecore/
 http://xenon.colorado.edu/spotlight/index.php?product=spotlight&station=CHUR
 http://pixshark.com/funny-global-warming-cartoons-earth.htm
 Alley, Andrew, Brigham-Grette, Clarke, Cuffey, Fitzpatrick, Funder, Marshall, Miller,
Mitrovica, Muhs, Otto-Bliesner, Polyak, White, 2010. History of the Greenland Ice
Sheet: paleoclimatic insights. Quaternary Science Reviews 29, 1728-1756.