Info

2200 2300 2400 2500 2600 2700 2800 2900 Calendar years B.P.

rate radiocarbon year-calendar year calibration curve. This problem is particularly acute prior to the last glacial maximum (about 20,000 years ago). Several data sets from various natural sources have been proposed for calibration use, but no two data sets agree sufficiently to establish a consensus (13).

Scientists attempting to take advantage of the available IntCal98 calibration curve to establish subcentennial resolution chronologies must become more familiar with the calibration curve and its inherent limitations. In many circumstances, radiocarbon dates on a series of carefully chosen samples will allow considerable refinement of the derived calendar ages through constraints imposed by a priori information (such as stratigraphy) or by the pattern of the radiocarbon dates relative to calibration curve variations (an approach that is sometimes referred to as "wiggle-matching"). Even with the implementation of such methods, the establishment of reliable chronologies with centennial or better resolution will require substantial diligence and the devotion of appropriate resources to overcome the inherent limitations in the conversion of radiocarbon dates to calendar ages.

References and Notes

1. W. F. Libby, E.C.Anderson.J. R.Arnold, Science 109,227 (1949).

2. M. Stuiver, H.A. Polach, Radiocarbon 19,355 (1977).

3. M. Stuiver, P. D. Quay, Earth Planet. Sci. Lett. 53, 349 (1981).

4. M. Stuiver, P.J. Reimer, Radiocarbon35,215 (1993).

5. E. S. Deevey et al., Proc. Natl. Acad. Sci. U.S.A. 40,285 (1954).

7. M. Stuiver, H. E. Suess, Radiocarbon 8, 534 (1966).

9. P. M. Grootes, M. Stuiver, J. Geophys. Res. 102, 26455 (1997).

12. This simple exercise uses the tree-ring portion of the IntCal98 calibration curve. This portion is constructed entirely from Northern Hemisphere trees. However, the seasonal migration of the intertropical convergence zone will yield a mixture of Northern Hemisphere and Southern Hemisphere air in the tropics (14). The Northern Hemisphere-Southern Hemisphere difference averages 41±14 years between 1850 and 950 A.D. but varies from ~8 to -80 years for any given decade (15).

13. P.J. Reimer, Radiocarbon44,653 (2002).

14. J.A.Westbrook, T. P. Guilderson, P. A. Colinvaux, IAWA Bulletin, in press.

16. This manuscript benefited from discussions with the IntCal 2004 and the MESH Abrupt Climate Change working groups. We thank B. Thunell for reviewing an early draft of this manuscript, and the criticisms and comments of two anonymous reviewers. Funding provided by the U.S. National Science Foundation's ESH Program (ATM-0407554) and the University of California's Lawrence Livermore National Laboratory (contract W-7405-Eng-48).

Supplementary Online Material

www.sciencemag.org/cgi/content/full/307/5708/362/DC1

Table S1

10.1126/science.1104164

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