Melting of the Greenland Ice Sheet Christine Chen July 8, 2012 40% surface melt extent over ice sheet July 12, 2012 97% surface melt extent over ice sheet

Melting of the Greenland Ice Sheet

Christine Chen

July 8, 201240% surface melt extent over ice sheet

July 12, 201297% surface melt extent over ice sheet

OverviewAlley et al.1 Sundal et al. 2

Topic approach on a temporal scale

Historical, Mka and forward

Recent trends, 1993, 1995-1998

Evidence or Data Paleoclimate records, supplemented by modeling efforts

Remote sensing and modeling

Topic approach on a spatial scale

Wide, whole ice sheet considered

Narrow, 6 glaciers in southwest Greenland

Nature of argument Applied, inference of past climate conditions based on paleoclimate records

Applied and theoretical , construction of model to explain physical mechanisms behind movement of imagery

Publication type Literature Review Traditional Research

1Alley, R. B., Andrews, J.T ., Brigham-Grette J., Clarke, G.K.C., Cuffey, K. M., Fitzpatrick, J.J., Funder, S., Marshall, S.J., Miller, G.H.,Mitrovica, J.X., Muhs, D.R. Otto-Bliesner, B.L., Polyak, L., White, J.W.C. History of the Greenland Ice Sheet: paleoclimatic insights. Quaternary Science Review. 29, 1728-1756 (2010).2Sundal, A. V., Shepard, A., Nienow, P., Hanna, E. Palmer, S., & Huybrechts, P. Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage. Nature. 469, 521-524 (2011). Doi: 10.1038/nature09740














History of the Greenland ice sheetice-sheet onset and early fluctuations

CO2

Warm to high latitudes

“such warm temperatures preclude permanent ice near sea level”

Before 65 MaM=Mega=106= 1 million)

~7.3 Ma

Warm period

Coolperiod

Ice-rafted debrisOcean coring

~46 Ma

~38-30 Ma

~46 Ma - ~7.3 Ma


CO2




~7.3 Ma

Warm period

Coolperiod

Ice-rafted debrisOcean coring

~46 Ma

~38-30 Ma

~46 Ma - ~7.3 Ma


CO2




Warm period

~7.3 Ma

~46 Ma

~38-30 Ma

“Greenland seems to have supported at least some glaciation since at least 38 Ma”

Coolperiod


~2.4Ma

Kap Kobenhavn Formation of North Greenland

“Funder 2001 postulated complete deglaciation of Greenland”

Warm period

Boreal biotic fossil

History of the Greenland ice sheetthe most recent million years

[prior to MIS 5e]

Marine Isotope Stages (MIS)

•Dating technique based on δ18O of a marine indicator, benthic foraminifera

History of the Greenland ice sheetthe most recent million years – far-field sea-level indications

marine deposits

21 m above modern sea leveldated to MIS 11

marine deposits

22 m above modern sea levelPossibly dated to MIS 11

Oxygen-isotope and faunal data Higher than present sea leveldated to MIS 11

“These results, taken together, if accurate, imply that all of the Greenland Ice sheet, all of the West Antarctic ice sheet, and part of the East Antarctic ice sheet disappeared at this time”

Warm period

Warm period

Warm period

History of the Greenland ice sheetthe most recent million years – far-field sea-level indications

Coral from a fossil reef

“MIS 9 sea level was close to but not much above the present level”

dated to MIS 9

Coral-bearing marine deposits

~2 m above sea level

“sea level stood close to its present level during MIS 7”

dated to MIS 7

“Taken together, these data point to MIS 11 as a time when sea level likely was notably higher than now…if so, melting of most or all Greenland’s ice seems likely”

Pleasant point in Florida Bay

Warm period

Warm period

History of the Greenland ice sheetthe most recent million years – ice-sheet indications

Ice cores

“suggest a major retreat”dated to MIS 11

Marine sediment records

“point toward MIS 11…as the most likely time of anomalous warmth”

dated to MIS 11

“data strongly indicate that Greenland’s ice was notably reduced sometime after extensive ice coverage and large ice ages began, while temperatures surrounding Greenland were not grossly higher than recently”

Central Greenland

Warm period

Warm period

North Atlantic

East Greenland

Glacial deposits

dated to MIS 6

Cold period

Support view of most extensive ice in Greenland in MIS 6

History of the Greenland ice sheetmarine isotope stage 5e



History of the Greenland ice sheetmarine isotope stage 5e – far-field sea-level indications

MIS 5e

Warm periodFlorida Keys Coral reefs

“during MIS 5e local sea level was at least 6 m higher than modern-day sea level”

Walking through an example…

Conservative estimate

History of the Greenland ice sheetmarine isotope stage 5e – ice sheet changes

“The MIS 5e Greenland Ice Sheet covered a smaller area than now, but by how much is not known with certainty.”

Ice cores

Cuffey and Marshall (2000) try to determine climate conditions-using ice core data as constraints -oxygen isotope ratio = f(elevation of ice-sheet surface , temperature change at a constant elevation)

History of the Greenland ice sheetpost-MIS5e cooling to the last glacial maximum (LGM or MIS2)



History of the Greenland ice sheetpost-MIS5e cooling to the last glacial maximum (LGM or MIS2) – climate forcing

Ice cores Ocean coring

“A general cooling from MIS 5e (~123 ka) to MIS 2 (coldest temperatures were at ~24 ka in Greenland)”

History of the Greenland ice sheetpost-MIS5e cooling to the last glacial maximum (LGM or MIS2) – ice-sheet changes

Scoresby Sund region East Greenland

Best records of ice-sheet response

History of the Greenland ice sheetice-sheet retreat from the last glacial maximum (MIS 2)



History of the Greenland ice sheetice-sheet retreat from the last glacial maximum (MIS 2) – ice-

sheet changes

Ice rafted debris(IRD)

Summary of Fig 12:Early debris inputsMid-Holecene -> very little debrisLate Holecene -> steady delivery of debris

Figure 8Figure 12

“The Greenland Ice Sheet lost ~40% of its area and notable volume after the last glacial peak ~24-19 ka.”

Break for Discussion

Summary for

Question: What causes melting over the Greenland ice sheet?

Conclusion: “…in the suite of observations as a whole, the behavior of the Greenland Ice Sheet has been more closely tied to temperature than to anything else…However the data do not preclude the possibility that local or regional events may at times have been controlled by precipitation”

Evidence: Paleoclimatic indicators, both marine and terrestrial














-sends radio wave pulses-many echo waveforms received successively at different antenna positions

Synthetic Aperture Radar (SAR)

How does surface melt relate to ice flow? Background:

Previous research led to contradictory statementsmelt increases flow increases“basal lubrication”melt decreases flow increases

Revelation:“melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient”

Timeframe:1993, 1995-1998

Sundal et al.-”significant flow increase in summer relative to winter at all six glaciers”-”marked decrease in the variance of ice speed in winter compared to summer”

Sundal et al. -Run-off data extracted from a model

-high run-off and melt-extent = “high-melt year”1995,1998 = “high melt year”1993,1996,1997=“low melt year”

High melt year

Low melt year

“seasonal velocity fluctuations are broadly coincident with fluctuations in the degree of surface melting”

Early Late

Summer

Late summer speed up is markedly low in high melt (warm) years

“Switch from inefficient (cavity) to efficient (channelized) mode of drainage”

Summary for

Question: How to improve simulations of the Greenland ice-sheet flow under climate warming scenarios?

Conclusion: “…should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet’s response to climate warming.”

Evidence: SAR imagery and modeling

Break for Discussion – End

Thoughts from this seminar…What makes studying climate problems so difficult?

• Dealing with a Complex System – Acts on many different spatial scales

• earth-sun system• atmosphere-ocean interactions

—Acts on many different temporal scales– Many components interacting with each other at the same time

• Tool limitations — assumptions and simplification in modeling— assumptions in classifying in remote sensing — weather conditions for in situ data

• Data limitations— Incomplete data sets

• Funding— Different data types

• Challenges in combining them

Break for Discussion – End

Documents

Melting of the Greenland Ice Sheet Christine Chen July 8, 2012 40% surface melt extent over ice sheet July 12, 2012 97% surface melt extent over ice sheet