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,

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. ThibaultUndergraduateAtmospheric Science and Anthropology

Flight PlanIntroduction Paper Summary Questions

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The Greenland Ice Sheet OverviewDimensionsArea ~ 1.7 million km2Average thickness ~ 1600 mVolume ~ 2.9 million km3

GeologySome bedrock depressed below sea levelRests on bedrock above sea level

CompositionOld snow squeezed under bulk of new snow

The Greenland Ice Sheet OverviewPrimary Mass Loss ContributorsLow-elevation meltingCalving icebergs

Recent TrendsIncreasing temperaturesGreater snowfallMore runoff from meltwaterMass balance losses intensifying

Intergovernmental Panel on Climate Change (IPCC), 2007Mass Balance1961-2003+25 to -60 Gt(-0.07 0.17 mm SLE)1993-2003-50 to -100 Gt(0.14-0.28 mm SLE)2005Even worseThe Greenland Ice SheetIce Sheet BehaviorInternal Deformation, Meltwater, Friction, and Ice Shelves

The Greenland Ice SheetIce Sheet BehaviorIce Flow ModelsProcesses not includedAs a result, projections are not accurate

IPCC (2007) on sea level projectionsDo not take future rapid dynamical changes in ice flow into accountNo upper bound for rising sea level

The Greenland Ice SheetEstimates of Ice Sheet Mass Balance over time

Merged South and West Greenland Temperature RecordNote: -360 Gt/a = 1mm SL riseThe Greenland Ice SheetIce Sheet BehaviorIf Ice Sheet margins are fixed:Center of the ice sheet is not very sensitive to forcingsAccumulation increases ice thickness and increases slope on the ice sheetConsequently, ice discharge increases

If Ice Sheet margins change:Slope will increase or decrease which affects flow rateMargins can experience effects quicklyCentral regions experience effects slowlyThe Greenland Ice SheetIce Sheet BehaviorDeformation is faster in warmer ice

In inland areas deformation Is slowed by coolingCauses ice to thicken May steepen ice sheet to increase ice flux

Deep ice may not feel effects for millenniaPenetration timeTemperature is not stationarySurface melt

.

How do we address all this uncertainty? Paleoclimatology

Paleoclimatic IndicatorsMarineTerrestrialGeomorphicBiological Glacial Isostatic Adjustment and Sea LevelFar Field Sea LevelGeodeticIce Cores


Span: less than 15 ka

Provide data for:

Flux and Ice-Rafted Debris (IRD)Glacial deposition on trough-mouth fansStable-Isotopic and Biotic DataGeophysical data


More terrestrial indicatorsMore discontinuousLand: Net ErosionOcean: Net Depositon


MorainesStriated SurfacesBouldersLandform AppearanceGlacier elevation Limits of glaciationGlacier ExtentProxy for temperature


Lake SedimentsContinuous recordDetailed recordIsotopic CompositionMicro and Macro fossilsShell typeClimate data temperature



Records a two-fold historyGlacial-Isostatic adjustmentOcean VolumeHigh Water Marks

CoralsDirectly dated three ways500,000 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.


GPSSatellitesTide GaugesEarths Rotation


18O:16O ratio TemperaturePrecipitationVery ReliableTrapped GasestemperatureLayer ThicknessAccumulation ratesAgeElevation historyHow were these Paleoclimatic Indicators Used in the Context of this Paper?

History of the Greenland Ice SheetEarth has experienced periods of great warming in the past.

History of the Greenland Ice SheetInterglacial periods mean higher sea levels

MIS 11 (~ 400,000 ya)

Higher sea levels than nowMarine deposit from AlaskaOxygen Isotope and Faunal data

LongOrbital forcing

Comparable to Modern Temp.Within 1-2 oC

Indicates that Greenland Ice Sheet disappeared completely!

History of the Greenland Ice SheetMIS 9 (303-331 ka)Poorly constrained

Conflicting EvidenceCorals in BarbadosFringing Reefs on Henderson IslandHigher Sea LevelCoral on Fossil Reef at Florida Bay, Pleasant PointClose but not higher Sea LevelSea 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 VarvelHistory of the Greenland Ice SheetMIS 6 ( ~ 130-188 ka)Most extensive Ice in Greenland (probably)EvidenceGlacial deposits in East GreenlandNo Paleoclimatic ice sheet reconstructions are available

MIS 5 ( ~ 74-130 ka)Sea water moved inland During MIS 6 MIS 5 transitionMarine deposits and glacial deposits are preservedHigher temperatures in Greenland than far-field SSTs

Greenland Does Not Have A Continuous Climate Record

History of the Greenland Ice SheetMIS 5e (123 ka)

Sea Level High Stand

Coral and Reef dataW. Australia ~ 4 mBahamas ~ 5 mBermuda ~ 2-3 mFlorida 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 EstimatesHistory of the Greenland Ice SheetHowever, the previous sea level estimations did not take Glacial-Isostatic Adjustment into consideration.Bayesian Statistical ApproachAccounts for scant and noisy dataDerived local and globally averaged sea level (GSL) covarianceResults for MIS 5eGSL exceeded6.6 m (95%)8.0 m (67%)9.4 m (33%)

Conditions in GreenlandMIS 5e Temperatures Terrestrial Data (CAPE 2006)

Peak: ~ 130 ka

Summer (higher than recent)NW Greenland: ~ 4 oCE Greenland: ~ 5 oCMarine: ~ 2-3 oCClimate SimulationsSummer Sunshine

Predicted maxima: 4-5 oCFor NW, E and Marine parts of Greenland

~3 oCFor everywhere else

Conditions in GreenlandAs the world entered MIS 5e, Greenland began undergoing deglaciation.

Attributed to climate forcing

Resulted from combination of Greenland deglaciation and far-field land iceIce Sheet ChangesMIS 5e Ice Sheet was smaller

By how much?Uncertain because of lack of continuous Paleoclimatic dataUnknown Key ConstraintsTemperaturePrecipitationIce flow factors

Many Theories

Conditions in GreenlandBasic Theory is from Marshall and Cuffey (2000)ApproachUsed isotope ratios as constraintsDepend on elevation and temperatureGenerated climate and ice-sheet historiesProblemsDepended on isotopic sensitivity parameter Past accumulation rates estimatedLarge uncertainties Ice flow was not considered Model produced smaller than observed scenariosDriven by only one recordConditions in GreenlandAnother theory was developed by Otto-Bliesner et al (2006)New ApproachCoupled ocean-atmosphere climate modelTested output against Paleoclimate data from around Greenland Ice SheetDid not have to use a sensitivity parameter for relating temperature to isotopic compositionDid not have to assume snow accumulation and temperatureConsiders Milankovich changes in radiation insolation as a primary forcing

Modeled Greenland Ice Sheet Configurations

Conditions in GreenlandResultsProduced Reconstructions that corresponded to Greenland and Arctic dataCuffey and Marshall found MIS 5e to be snowy and very warmor 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 modelBest estimate of MIS 5e ConditionsSea Level : 3-4 mTemperature: 3 oC 4 oC

Climate ForcingReconstructions from periods more recent than MIS 5e have better confidence.

Ice core records are especially helpful

Near-field marine records are not as robustRarely span more than 130,000 yearsCore HU90-01318O isotope change indicates cooling after MIS 5e Greenland Cores

Climate ForcingThe Big PictureCooling from MIS 52 to MIS 2 (123 ka)Warming Mid-Holocene/MIS 1 (millennia)Cooling in Little Ice Age (centuries )Warming

42Greenland Cores

Near-Surface Plankton Oxygen-18 Isotopes Renland Ice Cap

Greenland Cores

Oxygen 18 Isotope CoresNW Labrador Sea

Greenland Cores

Oxygen 18 Isotope CoresDavis Strait

Climate ForcingIce Isotope Records

GreenlandByrd Station, AntarcticaIce Sheet ChangesGreenland Ice SheetExpanding when coolingRetreating when warming

Cooling led to more ice volumeCore total gas contentIce flow variables

Glacial MarginsRetreat means thinner central regionsAdvance means thicker central regions

Ice Sheet ChangesUncertainties

Ice extent and advance on Continental Shelf

Rates and Times of Responses to short-lived climate changesSince the Last Glacial MaximumColdest conditions occurred 24,000 years agoHeinrich Event H2

Since then, temperatures have fluctuatedEarths orbitExpanded wintertime sea iceVariations in Magnetic Susceptibility and Oxygen 18 Isotopes

PresentLast Glacial MaximumIce Rafted Debris Inputs

Conclusion:The Greenland Ice Sheet has been changed significantly over many past climatic eras.Paleoclimatic Data Indicates:TemperatureCooling Ice Sheet growsWarming Ice Sheet shrinksLarge Warming Ice Sheet lossControl applies for current as well as higher past temperaturesSea LevelRising 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 extentGreater snowfall means less iceIs NOT the primary forcing

Sea Level change does NOT dominate Temperature forcingIn recent millennia, fluctuations in ice sheet margins fit pattern of Temperature forcingExpectations of Sea Level change forcing does not fit patternIs NOT the primary forcing

Temperature is the dominant forcing in both the short-term and the long-term.

Temperature vs. Volume

ConclusionsThey arent exactly ecstaticGreenland Ice Sheet will shrink because of warmingEven a few degrees will tip it over the edge

Problems: We dont know anything!Specific numerical constraints Established error boundsRate of ice sheet loss

More Data Reconnaissance and Analysesare Needed.My OpinionA 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 techniquesNeed more people to become involved in field for data analysis

Thank you very much!Questions?Referenceshttp://www.cartoonstock.com/cartoonview.asp?catref=gra061031http://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-dischargehttp://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=86709http://research.bpcrc.osu.edu/Icecore/http://xenon.colorado.edu/spotlight/index.php?product=spotlight&station=CHURhttp://pixshark.com/funny-global-warming-cartoons-earth.htmAlley, 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.

Documents

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,