1. Modeling of present and Eemian stable water isotopes in precipitation
Jesper Sjolte
PhD student
Sigfús J Johnsen
Centre for Ice and Climate
Niels Bohr Institute
University of Copenhagen
Denmark
Georg Hoffmann
LSCE CEA/CNRS
Saclay
France

2. Variability of seasonal and annual data
Overview REMOiso
The regional model
Model setup, domain, 'nudging' ect.
Climatology
Precipitation and accumulation
Temperature and isotopes
Variability of seasonal and annual data
Temperature and precipitation
Annual and seasonal mean δ18O
Main patterns of variability
PCA of model output
Relation with the NAO

3. Variability of seasonal and annual data
Overview REMOiso
The regional model
Model setup, domain, 'nudging' ect.
Climatology
Precipitation and accumulation
Temperature and isotopes
Variability of seasonal and annual data
Temperature and precipitation
Annual and seasonal mean δ18O
Main patterns of variability
PCA of model output
Relation with the NAO

4. REMOiso Model setup SSTs from meteorologic re-analysis or climatic
reconstruction
Global model
with isotopes
REMOiso
REMOiso
Regional climate model fitted with isotope diagnostics
Three different kinds of water H216O, H218O, HD16O
ERA-40 re-analysis

5. Model domain
~55km resolution

6. Variability of seasonal and annual data
Overview REMOiso
The regional model
Model setup, domain, 'nudging' ect.
Climatology
Precipitation and accumulation
Temperature and isotopes
Variability of seasonal and annual data
Temperature and precipitation
Annual and seasonal mean δ18O
Main patterns of variability
PCA of model output
Relation with the NAO

7. Precipitation: accumulation maps

8. Precipitation: mean annual cycle
REMOiso
Observations

9. Precipitation: mean annual cycle=

10. Spatial isotope-temperature slope

11. Climatology summary Precipitation Temperature Isotopes
REMOiso captures the overall spatial accumulation pattern
The differences in seasonal cycle along the Greenland coast is well represented by the model
Temperature
There is a warm bias of ~5°C in the central parts of the ice sheet
Isotopes
The modeled spatial slope for Greenland (0.70 ‰ per °C) is lower than the observed (0.81 ‰ per °C)‏
The warm bias of the temperatures is reflected by the less depleted isotopes

12. Variability of seasonal and annual data
Overview REMOiso
The regional model
Model setup, domain, 'nudging' ect.
Climatology
Precipitation and accumulation
Temperature and isotopes
Variability of seasonal and annual data
Temperature and precipitation
Annual and seasonal mean δ18O
Main patterns of variability
PCA of model output
Relation with the NAO

13. Variability of seasonal data
Percentage of inter-annual
seasonal variability explained
by the model for temperature
and precipitation
Summer:
May-Oct
Winter:
Nov-Apr

14. GRIP 1990-1993 DYE3 1980-1983 δ18O time series Snow pit Snow pit
REMOiso
REMOiso

15. Reykjavik δ18O time series
GNIP
data
REMOiso

16. Seasonal ice core δ18O
Ice core
data
REMOiso

17. Seasonal mean ice core δ18O
REMOiso
Ice core
data

18. δ18O and d-ecxess
d-excess = δD-8*δ180

19. δ18O and d-ecxess
δ180
d-excess

20. Coastal δ18O and d-ecxess mean annualcycle

21. Site G δ18O and d-ecxess mean annualcycle

22. Precipitation and temperature
Variability summary
Precipitation and temperature
During winter 5% to 81% of the temperature variability is explained by the model, while for precipitation 2% to 61% is explained
The model results are more in line with observations, where the re- analysis is expected to be most realistic
Isotopes
Up to 30% of the winter variability is explained by the model (Reykjavik)‏
Very depleted isotopic values are not captured by the model
Local effects e.g. sastrugi make comparison with ice cores data difficult
d-excess annunal cycle for agree for coastal areas but not for Site G

23. Variability of seasonal and annual data
Overview REMOiso
The regional model
Model setup, domain, 'nudging' ect.
Climatology
Precipitation and accumulation
Temperature and isotopes
Variability of seasonal and annual data
Temperature and precipitation
Annual and seasonal mean δ18O
Main patterns of variability
PCA of model output
Relation with the NAO

24. Principal Component Analysis: EOFs of model output

25. PCA of model output
Bo Vinther et al. submitted

26. PCA of model output

27. NAO correlation maps

28. Patterns of variability summary
EOF patters
The pattern for temperature is largely unimodal for Greenland with exception of the east coast
The precipitation pattern has a strong east-west contrast
Isotopes looks like a mixture of the temperaure and the precipitation pattern, and matches the pattern found in ice core data
NAO
The PC1s for winter data are highly correlated with the NAO
Temperature R2 = 0.44
δ18O R2 = 0.21
Precipitation R2 = 0.25
Furthermore the correlation maps for NAO resembles the PC patterns

29. Overview ECHAMiso The global model Modeled anomalies Model setup
Temperature and isotope maps
Seasonal cycle
Coparison to ice core data

30. Overview ECHAMiso The global model Modeled anomalies Model setup
Temperature and isotope maps
Seasonal cycle
Coparison to ice core data

31. Eemian experiments 115kyr, 122kyr and 126kyr
Global experiments
Eemian experiments 115kyr, 122kyr and 126kyr
ECHAMiso 4.5, T42 resolution ~2.8 degrees
Present ice sheet configuration ect.
Climatologic SSTs from IPSL_CM4 coupled model
Model runs: years
Orbital parameters adjusted to paleo-values
Preindustrial greenhouse gas levels p(CO2) = 280ppm

32. Overview ECHAMiso The global model Modeled anomalies Model setup
Temperature and isotope maps
Seasonal cycle
Coparison to ice core data

33. Eemian temperatures
years BP
years BP
years BP

34. Comparison with proxy temperatures

35. Eemian 18O
years BP
years BP
years BP

36. Temperature anomalies

37. 18O anomalies

38. 18O – temperature relation
[degree C/per mil]

39. SWI compared with ice core data
ECHAMiso o
Ice core data *

40. Summary: Eemian experiments
Simulated Eemian peak summer temperatures for the Northern Hemisphere fit the proxy data well
Limited response in simulated temperature for Antarctica
Simulated18O/D amplitude is too small compared to ice core data
Less of the 18O variability is explained by temperature for the 'warm' time slices 122kyr and 126kyr
Ice sheet dynamics, fresh water discharge and vegetation changes should be incorporated in future experiments to achieve more realistic boundary conditions

41. Updating REMOiso physics Palaeo experiments with REMOiso
What's next
Updating REMOiso physics
Palaeo experiments with REMOiso
Holocene
LGM
Eemian

42. THANK YOU!

43. The 'nudging' technique
The global model and the regional model are forced to follow
the upper level flow of the re-analysis

44. The 'nudging' technique
Daily temperatures from NorthGRIP 2nd half of 1997

45. Annual mean accumulation
Ice core
data
REMOiso

46. Annual mean ice core δ18O
Ice core
data
REMOiso

47. Positive NAO
Deep icelandic low and strong subtropical high

48. Negative NAO
Weak icelandic low and weak subtropical high