1. 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

2. Overview Alley et al. 1 Sundal et al. 2 Topic approach on a temporal scale Historical, Mka and forward Recent trends, 1993, 1995-1998 Evidence or DataPaleoclimate 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 argumentApplied, inference of past climate conditions based on paleoclimate records Applied and theoretical, construction of model to explain physical mechanisms behind movement of imagery Publication typeLiterature ReviewTraditional Research 1 Alley, 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). 2 Sundal, 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

3. Overview Alley et al. 1 Sundal et al. 2 Topic approach on a temporal scale Historical, Mka and forward Recent trends, 1993, 1995-1998 Evidence or DataPaleoclimate 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 argumentApplied, inference of past climate conditions based on paleoclimate records Applied and theoretical, construction of model to explain physical mechanisms behind movement of imagery Publication typeLiterature ReviewTraditional Research 1 Alley, 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). 2 Sundal, 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

4. History of the Greenland ice sheet ice-sheet onset and early fluctuations CO2 Warm to high latitudes such warm temperatures preclude permanent ice near sea level Before 65 Ma M=Mega=10 6 = 1 million) ~7.3 Ma Warm period Cool period Ice-rafted debris Ocean coring ~46 Ma ~38-30 Ma ~46 Ma - ~7.3 Ma

5. History of the Greenland ice sheet ice-sheet onset and early fluctuations CO2 Warm to high latitudes such warm temperatures preclude permanent ice near sea level Before 65 Ma M=Mega=10 6 = 1 million) ~7.3 Ma Warm period Cool period Ice-rafted debris Ocean coring ~46 Ma ~38-30 Ma ~46 Ma - ~7.3 Ma

6. History of the Greenland ice sheet ice-sheet onset and early fluctuations CO2 Warm to high latitudes such warm temperatures preclude permanent ice near sea level Before 65 Ma M=Mega=10 6 = 1 million) Warm period ~7.3 Ma ~46 Ma ~38-30 Ma Greenland seems to have supported at least some glaciation since at least 38 Ma Cool period

7. History of the Greenland ice sheet ice-sheet onset and early fluctuations ~2.4Ma Kap Kobenhavn Formation of North Greenland Funder 2001 postulated complete deglaciation of Greenland Warm period Boreal biotic fossil

8. History of the Greenland ice sheet the most recent million years [prior to MIS 5e] Marine Isotope Stages (MIS) Dating technique based on δ18O of a marine indicator, benthic foraminifera

9. History of the Greenland ice sheet the most recent million years – far- field sea-level indications marine deposits 21 m above modern sea level dated to MIS 11 marine deposits 22 m above modern sea level Possibly dated to MIS 11 Oxygen-isotope and faunal data Higher than present sea level dated 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

10. History of the Greenland ice sheet the 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 Greenlands ice seems likely Pleasant point in Florida Bay Warm period

11. History of the Greenland ice sheet the 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 Greenlands 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 North Atlantic East Greenland Glacial deposits dated to MIS 6 Cold period Support view of most extensive ice in Greenland in MIS 6

12. History of the Greenland ice sheet marine isotope stage 5e Marine Isotope Stages (MIS) Dating technique based on δ18O of a marine indicator, benthic foraminifera

13. History of the Greenland ice sheet marine isotope stage 5e – far-field sea- level indications MIS 5e Warm period Florida KeysCoral reefs during MIS 5e local sea level was at least 6 m higher than modern-day sea level Walking through an example… Conservative estimate

14. History of the Greenland ice sheet marine 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)

15. History of the Greenland ice sheet post-MIS5e cooling to the last glacial maximum (LGM or MIS2) Marine Isotope Stages (MIS) Dating technique based on δ18O of a marine indicator, benthic foraminifera

16. History of the Greenland ice sheet post-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)

17. History of the Greenland ice sheet post-MIS5e cooling to the last glacial maximum (LGM or MIS2) – ice-sheet changes Scoresby Sund region East Greenland Best records of ice-sheet response

18. History of the Greenland ice sheet ice-sheet retreat from the last glacial maximum (MIS 2) Marine Isotope Stages (MIS) Dating technique based on δ18O of a marine indicator, benthic foraminifera

19. History of the Greenland ice sheet ice-sheet retreat from the last glacial maximum (MIS 2) – ice-sheet changes Ice rafted debris (IRD) Summary of Fig 12: Early debris inputs Mid-Holecene -> very little debris Late Holecene -> steady delivery of debris Figure 8 Figure 12 The Greenland Ice Sheet lost ~40% of its area and notable volume after the last glacial peak ~24-19 ka.

20. 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

21. Overview Alley et al. 1 Sundal et al. 2 Topic approach on a temporal scale Historical, Mka and forward Recent trends, 1993, 1995-1998 Evidence or DataPaleoclimate 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 argumentApplied, inference of past climate conditions based on paleoclimate records Applied and theoretical, construction of model to explain physical mechanisms behind movement of imagery Publication typeLiterature ReviewTraditional Research 1 Alley, 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). 2 Sundal, 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

22. -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 statements melt 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

23. 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

24. 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

25. 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 sheets response to climate warming. Evidence: SAR imagery and modeling Break for Discussion – End

26. 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