David Schneider and Eric Steig

1. Isotopic Records in US-ITASE Cores: A preliminary report WAIS Workshop September, 2003 David Schneider and Eric Steig University of Washington

2. Annual mean Accumulation at US-ITASE Sites (cm^3 water-equivalent) Figure courtesy Dixon, Kaspari, Spikes.

3. δ18O From 2001-5

4. 2001-5 δ18O Dating of ice core: Based on summer sulphate and isotopic peaks.

5. Climatology (1982-1999) of temperature and δ18O at 2001-5 δ18O = .19*T - 26‰ r = .92

6. Mean annual temperature- δ18O relationship?

7. Mean annual temperature- δ18O relationship? T δ18O

8. δ18O record at 2000-1 (near proposed WAIS deep core)

9. Temperature variability at 2000-1 and 2001-5

10. Isotopic variability at 2000-1 and 2001-5

11. Interannual temperature variability in Antarctica

12. Isotopes from 2000-1 and reconstructed PC’s of Antarctic temperature r = .40 winter r = .28 annual

13. Two cores are better than one r = .37 annual; .39 winter R-pc1 annual mean Linear combination of 01-5 and 00-1

14. Three cores are better than two r = .54 annual; .52 winter R-pc1 annual mean Linear combination of 01-5 and 00-1 and Law Dome

15. Summary: • The cores can be well-dated with summer sulphate peaks, corroborated by isotopic annual cycles • Isotopic records exhibit a robust climatological relationship with the seasonal temperature cycle; a spatial relationship can be obtained once more cores are analyzed.

16. Summary: • The cores can be well-dated with summer sulphate peaks, corroborated by isotopic annual cycles • Isotopic records exhibit a robust climatological relationship with the seasonal temperature cycle; a spatial relationship can be obtained once more cores are analyzed. • The temporal isotopic-temperature slope appears to be much smaller than the traditional Dansgaard spatial slope (~0.2 vs ~0.64). • On seasonal to interannual timescales, temperatures at sites 2001-5 and 2000-1 are well correlated

17. Summary: • The cores can be well-dated with summer sulphate peaks, corroborated by isotopic annual cycles • Isotopic records exhibit a robust climatological relationship with the seasonal temperature cycle; a spatial relationship can be obtained once more cores are analyzed. • The temporal isotopic-temperature slope appears to be much smaller than the traditional Dansgaard spatial slope (~0.2 vs ~0.64). • On seasonal to interannual timescales, temperatures at sites 2001-5 and 2000-1 are well correlated • However, annual mean isotopic values are not well-correlated with annual mean temperatures at the site or between sites but the two cores agree better with Law Dome than with each other.

18. Summary: • The cores can be well-dated with summer sulphate peaks, corroborated by isotopic annual cycles • Isotopic records exhibit a robust climatological relationship with the seasonal temperature cycle; a spatial relationship can be obtained once more cores are analyzed. • The temporal isotopic-temperature slope appears to be much smaller than the traditional Dansgaard spatial slope (~0.2 vs ~0.64). • On seasonal to interannual timescales, temperatures at sites 2001-5 and 2000-1 are well correlated • However, annual mean isotopic values are not well-correlated with annual mean temperatures at the site or between sites. • Larger-scale measures of temperature variability (i.e. PC’s) show a better correlation with isotopic ratios than local T or circulation patterns alone. • Preliminary correlations of three ice cores with leading PC’s of Antarctic temperatures suggests ice core-based temperature reconstructions may agree well with station-based temperature reconstructions. • Rather than having conflicting information, these cores probably have complimentary information.

20. Multiple parameters in core 2001-5 T δ18O H2O2 SO42- 2002 1992 1982 Figure courtesy Dixon

21. Mean annual accumulation and δ18O at 2000-1 r = .21

22. Ongoing work: • Continue isotopic measurements on ITASE cores (21 sites!!) • More calibration exercises • Better understanding/interpretation of controls on interannual variability in isotopic ratios • Reconstruction of last 200-500 years of Antarctic climate variability

23. Annual mean temperature -60 -50 -40 -30 -20 °C from AVHRR

24. Monthly (1982-1999) regression between local temperature and δ18O at 2001-5 r = .59

25. Climatology of temperature- δ18O at 2000-1 r = .92

26. Mean annual temperature- δ18O at 2000-1 δ18O T r = .30

27. Power spectra: 2000-1 Annual cycle Semiannual cycle

28. Depth-age scales for 01-5

29. Power spectra: 2001-5 Annual cycle Semiannual cycle

30. Significant low-frequency variability?

31. Something about Hercules Dome (2002-4) • Could be easier than WAIS to relate to large-scale variability • But is the accumulation rate too low?

33. Spatial temperature-elevation relationship

34. What determines isotopic ratios in an ice core? • Temperature when precipitation forms • Traditional to use mean annual surface temperature • May be better idea to use inversion temperature

35. What determines isotopic ratios in an ice core? • Temperature when precipitation forms • Traditional to use mean annual surface temperature • May be better idea to use inversion temperature • Timing of accumulation events; amount of precipitation • Temperature of source (place of evaporation) • Distance/pathway from source to deposition site

36. Multiple parameters in core 2001-5 Figure by Dixon