CONCLUSIONS

The new ice-core records being obtained from the summit of the Greenland ice sheet promise to provide a 200,000-year history of changes in climate and environmental conditions over the Greenland ice sheet and in the North Atlantic basin, in unprecedented detail. To utilize this information for the determination of global climate and its variability on all time scales, we need to find first the spatial variability in the ice-core properties, and second the relationship between the ice-core records and paleoclimatic records from ocean sediments and terrestrial sources elsewhere on the globe. For the first we must study ice cores from different parts of Greenland and the Arctic, from lower-latitude, high-altitude ice caps, and especially from Antarctica. For progress toward the second, active collaboration among the glaciologic, the oceanographic, and the terrestrial paleoclimate research communities is needed. In view of the many and very rapid climate changes observed in the ice-core record, it is crucial to obtain accurate and detailed independent time scales for all paleoclimate records so that they can be used in intercomparisons. The detailed information on past changes in climate and environment will then allow us to study not only the major glacial-interglacial climate changes but also climate variability on decade-to-century time scales, and to develop an understanding of the causes and mechanisms of such changes.

ACKNOWLEDGMENTS

This work was supported by NSF grants DPP-8822073 and DPP-8915924, Division of Polar Programs. I thank my GIPS co-principal investigators and L. G. Thompson for contributing their results, and P. A. Mayewski for critical comments.

Discussion

WALLACE: Are there cores from ice sheets in other Northern-Hemisphere locations, such as Alaska, comparable to these Greenland cores?

GROOTES: There are several cores from ice masses in other Northern Hemisphere locations, though none of them is as long and detailed as the Greenland cores. A core drilled by Holdsworth on Mount Logan in Canada provides a record of about 1000 years. Of the three lower-latitude cores drilled by Thompson, the tropical Quelccaya ice cap in Peru covers about 1500 years, and the two cores in China, Dunde and Guliya, go back well into the last glacial period. Also, there are cores in the Canadian Arctic on Devon Island and the Agassiz and Barnes ice caps, and others on Svalbard, Novaya Zemlya, and Severnaya Zemlya. Several of these cores come from lower elevations that have summer melting, so the climate record is less well preserved.

BRYAN: Do the earlier cores, like those Dansgaard analyzed, correspond with your findings?

GROOTES: On a large scale we found the d18O and conductivity of the ice to be quite close for the different cores. In details, though, you find quite different signatures for the various locations. To understand the details of atmospheric circulation, we need a multitude of cores from different locations and elevations so we can distinguish local phenomena and more general patterns. The Quelccaya records in the Southern Hemisphere go back about 1500 years, and I'd say there's the potential in the high Andes for going back to 2000 years.



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