REFERENCES AND NOTES ___________________________ 1. W. Dansgaard et al., Nature 364, 218 (1993); Green- land Ice-core Project Members, Nature 364, 203 (1993); P. M. Grootes, M. Stuiver, J. W. C. White, S. Johnsen, J. Jouzel, ibid. 366, 552 (1993); M. Stuiver, P. M. Grootes, T. F. Braziunas, Quaternary Res. 44, 341 (1995). 2. R. B. Alley et al., Nature 362, 527 (1993). 3. E. J. Brook, T. Sowers, J. Orchardo, Science 273, 1087 (1996); J. Chappellaz et al., Nature 366, 443 (1993); P. A. Mayewski et al., Science 261, 195 (1993). 4. G. Bond et al., Nature 365, 143 (1993); S. J. Leh- mann and L. D. Keigwin, ibid. 356, 757 (1992); K. A. Hughen, J. T. Overpeck, L. C. Peterson, S. Trum- bore, ibid. 380, 51 (1996); R. J. Behl and J. P. Ken- nett, ibid. 379, 243 (1996). 5. L. D. Keigwin and G. A. Jones, J. Geophys. Res. 99, 12397 (1994); W. B. Curry and D. W. Oppo, Pale- oceanography 12, 1 (1997). 6. A. E. Bainbridge, GEOSECS Atlantic Ocean Expedi- tion, Vol. 2, Sections and Profiles (Government Print- ing Office, Washington, DC, 1980). 7. E. A. Boyle and L. D. Keigwin, Science 218, 784 (1982); D. Oppo and R. G. Fairbanks, Earth Planet. Sci. Lett. 86, 1 (1987); Paleoceanography 5, 277 (1990). 8. E. A. Boyle and L. D. Keigwin, Nature 330, 35 (1987). 9. J. C. Duplessy et al., Paleoceanography 3, 343 (1988). 10. M. Sarnthein et al., ibid. 9, 209 (1994). 11. D. W. Oppo and S. J. Lehman, Science 259, 1148 (1993). 12. J. E. Smith, M. J. Risk, H. P. Schwarcz, T. A. McCon- naughey, Nature 386, 818 (1997). 13. H. Cheng, J. F. Adkins, R. L. Edwards, E. A. Boyle, unpublished data. 14. S. D. Cairns and G. D. Stanley Jr., Proc. Fourth Int. Coral Reef Symp. Manila 1, 611 (1981). 15. Age screening was done by measuring 230 Th, 232 Th, and 238 U by isotope dilution in cleaned samples on an inductively coupled plasma-mass spectrometer at the Massachusetts Institute of Technology. 16. R. L. Edwards et al., Science 260, 962 (1993). 17. Samples were cleaned of exterior organic carbon and coatings of manganese/iron oxides with suc- cessive leaches in a 50:50 mixture of 30% peroxide and 1 M NaOH. A final short leach in a 50:50 mixture of peroxide and 1% perchloric acid was used to remove all remaining organic stains. These preclean- ing steps removed 15 to 25% of the original coral weight. Immediately before final dissolution and graphitization, corals were soaked in 10% HCl to remove an additional 7 to 30% of aragonite. This procedure overcomes contamination problems from modern carbon that result from storage and handling and organic carbon from polyp and crust material. Samples were carefully chosen to avoid secondary calcification from endolithic activity. 18. The 14 C/ 12 C ratio is expressed with the  notation, where  14 C is the per mil deviation from the 14 C/ 12 C ratio in 19th-century wood [M. Stuiver and H. A. Polach, Radiocarbon 19, 355 (1977)]. 19. J. F. Adkins and E. A. Boyle, Paleoceanography 12, 337 (1997). 20. E. Bard et al., Earth Planet. Sci. Lett. 126, 275 (1994); W. E. N. Austin, E. Bard, J. B. Hunt, D. Kroon, J. D. Peacock, Radiocarbon 37, 53 (1995); K. Gronvold et al., Earth Planet. Sci. Lett. 135, 149 (1995); H. H. Birks, S. Gulliksen, H. Haflidason, J. Mangerud, G. Possnert, Quaternary Res. 45, 119 (1996). 21. E. Bard, M. Arnold, R. Fairbanks, B. Hamelin, Radio- carbon 35, 191 (1993). 22. W. S. Broecker, G. Bond, M. Klas, G. Bonani, W. Wolfli, Paleoceanography 5, 469 (1990); G. E. Birch- field and W. S. Broecker, ibid. 5, 835 (1990). 23. M. Stuiver and H. G. Ostlund, Radiocarbon 22,1 (1980); W. S. Broecker, R. Gerard, M. Ewing, B. C. Heezen, J. Geophys. Res. 65, 2903 (1960). 24. We measured the spatial variation in Cd/Ca ratios from within a single modern D. cristagalli to check for vital effects. These biologically induced nonther- modynamic deviations from equilibrium for a par- ticular tracer have been found to dominate the sta- ble carbon and oxygen isotope signatures of deep- sea corals (12). A coral from 550 m in the South Pacific Ocean had an average Cd/Ca value of 0.172 mol/mol with 1 SD of 0.016 mol/mol. There was no within-coral spatial pattern to this variation. Although D. cristagalli may contain vital effects for Cd/Ca, this 10% SD is smaller than the signal in JFA 24.8 and does not have the top-to- bottom coherence we find in the 15.4-ka sample. For these reasons we believe sample JFA 24.8 has faithfully captured a change in the [Cd] of the past water masses. 25. The carbon isotopic ratio is defined as follows:  13 C = [( 13 C/ 12 C) sample /( 13 C/ 12 C) standard - 1]  1000, relative to the Pee Dee Belemnite standard [see H. Craig, Geochim. Cosmochim. Acta 3, 53 (1953)]. 26. The coral Cd distribution coefficient is the ratio of Cd/Ca in the coral to Cd/Ca in the water. Similar to a core top calibration in foraminifera, we measured Cd/Ca ratios in a suite of modern D. cristagalli that span a range of 0.5 to 3.2 M [PO 4 ]. Six of these coral fall on a line with a slope of 1.6 coral per water Cd/Ca ratio. This value implies a [PO 4 ] of 3.6 M for the top of sample JFA 24.8. However, there are three other samples from this calibration that have signifi- cantly higher Cd/Ca ratios in the coral than was pre- dicted by the water [Cd]. On the basis of this study, we believe the distribution coefficient for D. cristagalli is 1.6 or higher and that the 3.6 M [PO 4 ] estimate for JFA 24.8 is a maximum value. 27. W. S. Broecker, S. Blanton, M. Smethie Jr., G. Ost- lund, Global Biogeochem. Cycles 5, 87 (1991). 28. H. Kitagawa and J. van der Plicht, Science 279, 1187 (1998). 29. S. J. Lehmann and L. D. Keigwin, Nature 356, 757 (1992). 30. S. Lehman, personal communication. 31. L. D. Keigwin, G. A. Jones, S. J. Lehman, E. A. Boyle, J. Geophys. Res. 96, 16811 (1991). 32. AMS radiocarbon dates were measured by standard procedures at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrom- etry (CAMS). Ventilation ages were calculated with the 14 C projection age method described in (19). In three of the corals there is a slight elevation in initial  234 U, indicating a small degree of exchange with a high  234 U reservoir. From the observation that there is no significant correlation between 230 Th age and  234 U in different fragments of the same coral (13), we infer that the effect of this exchange on 230 Th age is small. 33. We thank S. Griffin, C. Masiello, and B. Grant for laboratory assistance. Discussions with D. Sigman, W. S. Broecker, and A. L. van Geen helped improve the manuscript. Supported by the National Science Foundation. J.F.A. was supported by a NASA Global Change fellowship and a grant from Tokyo Electric and Power Company. 18 November 1998; accepted 18 March 1998 Local Orbital Forcing of Antarctic Climate Change During the Last Interglacial Seong-Joong Kim,* Thomas J. Crowley, Achim Sto ¨ ssel During the last interglacial, Antarctic climate changed before that of the Northern Hemi- sphere. Large local changes in precession forcing could have produced this pattern if there were a rectified response in sea ice cover. Results from a coupled sea ice–ocean general circulation model supported this hypothesis when it was tested for three intervals around the last interglacial. Such a mechanism may play an important role in contributing to phase offsets between Northern and Southern Hemisphere climate change for other time intervals. One of the perplexing problems in Pleisto- cene climatology involves the factors re- sponsible for Antarctic climate change. Al- though orbital insolation variations play a major role in driving Pleistocene climate change (1), the precessional component of orbital forcing is almost out of phase be- tween the Northern Hemisphere (NH) and Southern Hemisphere (SH), so any condi- tions favorable for glaciation and deglacia- tion in the NH should result in the opposite response in the SH. For more than 20 years it has been known that although SH cool- ing in the Pleistocene accompanied NH glaciation, SH climate led NH climate into and out of the last (and other) interglacials. That is, the SH warmed and cooled before the NH (1). Carbon dioxide also increased before NH glacial retreat (2). Yet standard explanations for SH climate change rarely focus on local forcing changes around Ant- arctica. Most explanations involve more re- mote processes such as changes in atmo- spheric carbon dioxide concentration (3), variations in North Atlantic Deep Water (NADW) heat transport to the Antarctic (4), or lowering of sea level causing expan- sion of the Antarctic ice sheet. There is, however, a modest (1°C) contribution from mean annual changes in the local radiation budget at the highest latitudes as a result of synchronous NH-SH obliquity changes at the 41,000-year period (5). Here, we show that local forcing at the precessional period (19,000 and 23,000 years), which is out of phase between the NH and SH, may also be important in SH climate change. We based our study on the hypothesis that seasonal changes in the Ant- arctic summer may be proportionately more important than in the Antarctic winter be- cause sea ice is much closer to the freezing point in summer. This relation may allow a Department of Oceanography, Texas A&M University, College Station, TX 77843, USA. * To whom correspondence should be addressed. E-mail: ksj@ocean.tamu.edu SCIENCE  VOL. 280  1 MAY 1998  www.sciencemag.org 728