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 Thank You For Flying Today: Please Fasten Your Seat Belts and Secure Your Trays in an Upright Position. Enjoy the Ride!

The Greenland Ice Sheet Overview Dimensions Area ~ 1.7 million km 2 Average thickness ~ 1600 m Volume ~ 2.9 million km 3 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 to -60 Gt (-0.07 – 0.17 mm SLE) to -100 Gt ( 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 Core s

Paleoclimatic Indicators  Marine  Terrestrial Geomorphic Biological Glacial Isostatic Adjustment and Sea Level Far Field Sea Level Geodetic Ice Core s 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 Core s 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 Core s 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 Core s 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 Core s

Paleoclimatic Indicators  Marine  Terrestrial Geomorphic Biological Glacial Isostatic Adjustment and Sea Level Far Field Sea Level Geodetic Ice Core s 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 Core s 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 18 O: 16 O 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 o C Indicates that Greenland Ice Sheet disappeared completely!

History of the Greenland Ice Sheet MIS 9 ( 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 ( 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 ( ~ ka) Most extensive Ice in Greenland (probably) Evidence Glacial deposits in East Greenland No Paleoclimatic ice sheet reconstructions are available MIS 5 ( ~ ka) Sea water moved inland 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 Summer (higher than recent) NW Greenland: ~ 4 o C E Greenland: ~ 5 o C Marine: ~ 2-3 o C Climate Simulations Summer Sunshine Predicted maxima: 4-5 o C For NW, E and Marine parts of Greenland ~3 o C 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 oDepend 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 o C – 4 o C

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 HU O 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 gary-varvel-climate-change-scientists-on-ice/ / gary-varvel-climate-change-scientists-on-ice/ / Alley, Andrew, Brigham-Grette, Clarke, Cuffey, Fitzpatrick, Funder, Marshall, Miller, Mitrovica, Muhs, Otto-Bliesner, Polyak, White, History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Reviews 29,