1. Memorial University of Newfoundland
The Co-evolution of continental ice cover and 3D ground temperature over the last glacial cycle
Lev Tarasov
Memorial University of Newfoundland
(Thanks to A.S. Dyke, Richard Gyllencreutz, Oystein Lohne, Jan Mangerud, W. R. Peltier, and John Inge Svendsen)

2. Outline MOTIVATION: Ice-sheet evolution
What makes the model results meaningful?
PHYSICS: Glacial Systems Model (GSM)
DATA
BRIDGING DATA and PHYSICS: model calibration
SOME RESULTS

3. Questions What did the the northern Hemispheric ice-sheets do?
How do we find out?
How did the changing ice-sheets affect the ground temperature field?
How close to equilibrium is the present-day 3D ground temperature field?

4. Lot’s of poorly constrained components in the glacial system

5. Poorly constrained system; model pre(retro)dictions have generally lacked meaningful error bars => no meaningful interpretation. Solution: 3 components:

6. #1: Glacial Systems Model (GSM)
3D thermo-mechanically coupled ice-sheet model, 0.5 * 1.0 (lat/long) model resolution
VM2 viscosity model
detailed surface mass-balance and ice-calving modules
global gravitationally self-consistent RSL solver
fully coupled surface drainage solver

7. Model thermodynamics 3D ice thermodynamics
3D heat advection and vertical diffusion
Bed-thermal model
Vertical diffusion only
Non-uniform 20 layer grid spans 3 km
Deep geothermal heat flux field from Pollack et al (1993)
Simple: scalar thermal conductivity and heat capacity
Standard permafrost treatment using effective heat capacity
Parametrized TTOP model (based on Smith and Riseborough, 2002) for near surface ground temperature as a function of air temperature
Large-scale and Long-time scale
Horizontal resolution: 1 by 0.5 degrees

8. Climate forcing
Last Glacial Maximum (LGM) precipitation and temperature from 4 (6 for N. A.) highest resolution Paleo Model Intercomparison Project GCM runs
Mean and EOF fields
Present day observed fields

9. 120 kyr climate forcing (based ss09 chronology)

10. Embrace uncertainty: Lots of ensemble parameters
3(5 for North America) ice dynamical
13(16) regional precipitation
LGM precipitation EOFs most significant for North America
4(4) temperature
4(4) ice calving
4(2) ice margins
1 model version
= 29 (32)

11. Need constraints -> #2: DATA

12. Oct/06 margin chronology

13. Deglacial margin chronology
(Dyke, 2004)
36 time-slices
+/- 50 km uncertainty
Margin buffer
Margin forcing:
2 ensemble parameters control extent of adjustments to surface mass-balance
Calibration minimizes amount of margin forcing

14. RSL data; site weighting (A. S. Dyke and U. of Toronto RSL database)

15. Noisy data and non-linear system => need #3: calibration and error bars

16. Bayesian calibration
Sample over posterior probability distribution for the ensemble parameters given fits to observational data using Markov Chain Monte Carlo (MCMC) methods
Sampling also subject to additional volume and ice thickness constraints
North American calibration also uses strand-line observations

17. Large ensemble Bayesian calibration
Bayesian neural network integrates over weight space
effectively generate millions of model runs

18. LGM characteristics Dynamic ice-sheet
streaming constrained by sub-glacial till availability and thermodynamics
Large Keewatin ice-dome

19. Validation of glaciological model
RSL fits are overall as good as that of the non-glaciological ICE5-G model
North American model also validated against GRACE observations for present-day rate of mass-change
Surface topopgraphy similar to that infered on the basis of striations and landform orientation

20. Thermodynamic results (North American are published, Eurasian are preliminary)

21. Borehole comparison to observations (93. 72W, 51. 03N, with error bars

22. Caveat, dependence on thermal conductivity (66.64W, 50.21N)

23. Present-day permafrost distribution

24. Permafrost depth evolution: impact of surface ice

25. Present day proximity to equilibrium

26. European LGM ice-sheet (Problem: less ice-cover)

27. Kola Borehole Temperature profile

28. Kola latitudinal transect: Present Proximity to Equilibrium

29. Ice area evolution comparison : North America versus Europe

30. Summary Glaciological results North America: Large Keewatin ice dome
Dynamic ice-sheets
Permafrost/ground temperature:
Large variations in permafrost depth over glacial cycle
Results suggest southern half of the Laurentide ice-sheet was often extensively warm-based
Significant present-day dis-equilibrium
Impact of ice on present-day ground temperature field:
Is small outside of permafrost zone
Bayesian calibration method links data and physics (model) -> rational error bars
Calibration selects a climate forcing that produces a significantly different present day ground thermal field than that from a simple average of PMIP 1 and 2 General Circulation model results
For more results, refer to Tarasov and Peltier, JGR 2007

31. Request/Plea
Need an online database of deep borehole observations (especially for Eurasia)!!!!

32. Probability of warm based ice over last 20kyr for N.A.

33. Present-day permafrost distribution

34. Kola Transect: Present-day ice versus no-ice models

35. Kola borehole time transect

36. Present ensemble mean permafrost depth for Europe