1. GREENHOUSE GAS (CO 2, CH 4 ) AND CLIMATE EVOLUTION SINCE 650 KYRS DEDUCED FROM ANTARCTIC ICE CORES EPICA gas consortium J.-M. Barnola (1), U. Siegenthaler (2), E. Monnin (2), R. Spahni (2), J. Chappellaz (1),T.F. Stocker (2), D. Raynaud (2) and H. Fischer (3) (1)Laboratoire de Glaciologie et Géophysique de l’Environnement, Grenoble France (2)Climate and Environmental Physics, Physics Institute, Bern, Switzerland (3) Alfred-Wegener-Institut (AWI), Bremerhaven, Germany

2. How the gas are trapped ? What constraints do we have on the air trapping ? Implication on the phase relationship CO2 and CH4 records during the last climatic cycles Results based mainly from : Russian US French program of VOSTOK European programs GRIP (Greenland) and EPICA (Antarctica) Plan of the presentation

3. Antarctic Drilling sites Vostok Dome C Byrd Dome F DML

4. Densification and gas trapping Snow Firn Ice

5. Densification of polar firn : 3 main stages First meters : evaporation-condensation and surface diffusion Structural rearrangement by grain boundary sliding  0.35 <  < 0.55 g/cm 3 Plastic deformation of contact areas  0.55 <  < 0.85 g/cm 3 Plastic deformation of ice matrix surrounding cylindrical or spherical pores   ~ 0.92 g/cm 3 Good agreement between model and density measurements Model Snow : Alley Firn : Arzt (Arnaud et al., 2000)

6. Present day Close Off : Depth : 98 m Age : 2800 years Smoothing : ~ 250 years Full Glacial Close Off : Depth : 120 - 140 m Age : 6500 – 7400 years Smoothing: ~ 600 years

7. Under present-day conditions : - Gas are trapped 70 m (« warm » sites) 100 m (cold sites) below the surface. - Gas are trapped 200 yrs –3000 yrs after the snow deposition Air linked signals recorded deeper than ice linked signals. Air linked signals are younger than ice linked signals. Model prediction for glacial times : Gas trapped deeper than during present day due to colder condition. Gas age difference up to 7000 years due to lower accumulation. Possible constraints on close-off depth through gravitational and Thermal fractionation of permanent gas isotopes. ( Schwander et al, Sowers et al, Severinghaus et al )

8. Thermal and Gravitational fractionation at N-GRIP ( A. Landais et al, 2004 ) Convection zone Diffusion zone Non diffusive zone Close-Off Heavier molecules enriched in colder zone and in deeper part of the firn. In case of abrupt temperature change strong thermal gradient in the firn can exist which can be recorded by through the isotopic composition. See also Poster U. Seibt FF351

9. Model and isotopes are in good agreement in Greenland Different prediction during glacial times in Antarctica : Models predict deeper close off depth, while isotopes give thinner diffusive zone However : -From the comparison of different cores the modeled age at the close off is right - Isotopes and modeled firn ice thickness equivalent are the same (Blunier et al, Bender et al, G Dreyfus). Conclusion : Even if the model and isotopes disagree on the depth, the two approach are coherent for the age of the gas at the close off Comparison Models –Isotopes for the glacial conditions

10.  15 N allows to avoid the problem of the gas age-ice age difference CH 4 in phase with Greenland temperature CH 4 in Antarctic cores can be used as a time marker of Greenland Temp for the pre-Eemien times CH 4 - temperature timing from N 2 isotopes

11. Previous glacial periods High resolution Vostok CH 4 record shows millennial-scale variability during MIS 6 and MIS8 (periods of 2 to 7 kyr) Delmotte et al (2004) MIS 6MIS 8

12. During major stadials/interstadials, Antarctica warms up when Greenland is cool, and it starts to cool down when Greenland suddenly warms up Blunier et al., Nature, 1998 North-south correlation based on CH 4 Blunier et Brook, Science, 2001 Rahmstorf, Nature, 2002

13. Blunier et al., Nature, 1998 Modeled delta age Byrd :600 years Vostok : 6000 years The good agreement between ice linked and gas linked information adds confidence in modeled ages and phase relationships deduced Modeled delta age Byrd :600 years Vostok : 6000 years The good agreement between ice linked and gas linked information adds confidence in modeled ages and phase relationships deduced

14. Stadials and interstadials CO 2 :20 ppmv variability correlated with Antarctic temperature CH 4 :- 100-200 ppbv variability associated with North Atlantic climate shifts - synchronous with t° or lags by a few decades - increases over 50 to 150 yr Stauffer et al., 2002 and ref. therein TIME

15. Glacial-interglacial transition CO 2 : parallels Antarctic warming CH 4 : parallels N. Atlantic warming N 2 O : parallels N. Atlantic warming but with slower response than CH 4 Stauffer et al., 2002 and ref. therein TIME

17. 4 last Glacial-interglacial cycles from Vostok Maximum range of natural changes : CO 2 : 185-300 ppmv (~20 ppmv / °C) CH 4 : 350-800 ppbv (~75 ppbv / °C) N 2 O : 200-275 ppbv (~15 ppbv / °C) Steady-state information is useful, time-dependent information is even more ! Petit et al., Nature 1999 Time

18. Dome Concordia station seen By SPOT (not available on Google Earth)

21. 5 7 9 11 13 15 17 19 20 Dating by inverse modeling with 4 control windows Comparison with stacked marine record : Full glacial condition more constant than in marine record, interglacials cooler prior to stage 11. Time

23. Very good agreement between Dome C and Vostok

24. 280 ppmv 260 ppmv 180 ppmv 650 ppbv 600 ppbv 350 ppbv

25. CO2 : Relationship with antarctic temperature remains unchanged Glacial interglacial amplitude lower before stage 11 than after Full glacial concentration at the same level (185 ppmv) even if sea level is different Maximum at the very beginning of the last three interglacials CH4 : Relationship with antarctic temperature remains unchanged Glacial interglacial amplitude lower before stage 11 than after Full glacial concentration varies (as sea level do ?)

27. CO 2 : 40 ppmv change with minimum around 7-8000 yr BP CH 4 : 150 ppbv change with minimum around 5000 yr BP

28. CO 2 during the last millenium

29. CH4 during the last millenium

30. What is the link between CO2 variation and CH4 gradient ?

31. Main Conclusion : CO 2 and CH 4 Antarctic climate relation remains unchanged during the last 650 Kyrs allthough the features of glacial interglacial cycles have changed around Stage 11. Why CO 2 and CH 4 change : CO 2 : listen Peter Köhler and see poster from M. Leuenberger (EC-47) and from F. Joos (EC-24) CH 4 See posters from S Aoki (FF-213) and J Kaplan (EC-283)