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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 3, MARCH 1999

JOURNAL ARTICLES...
SEDIMENT RECORDS

Item #d99mar19

“A 0.5-Million-Year Record of Millennial-Scale Climate Variability in the North Atlantic,” J. F. McManus, D. W. Oppo, and J. L. Cullen,Science 283 (5404), 971-975 (1999).

Examination of continuous high-resolution marine sediment records of the subpolar North Atlantic shows the millennial-scale pacing of climate variability. A critical threshold of ice sheet size, iceberg discharge, and proxies of sea-surface conditions (the relative abundance of ice-raft debris and the benthic oxygen isotope of planktonic Foraminifera) show that only small ice-volume changes are associated with large-amplitude shifts in climate response and variability.

Item #d99mar20

“124,000-Year Periodicity in Terrestrial Vegetation Change During the Late Pliocene Epoch,” K. J. Willis, A. Kleczkowski, and S. J. Crowhurst,Nature 397, 685-688 (1999).

Spectral analysis of the lake sediments from Pula maar in Hungary provide a high-resolution continental record of late-Pliocene climate change (from 3 million to 2.6 million years ago) and the vegetative response during this period of global cooling. The analysis indicates a response of the terrestrial vegetation that has the same periodicities as the Earth’s obliquity and precession. It also shows a very strong response with a periodicity of about 124,000 years, a periodicity that would not reflect solar forcing. Rather, internally driven nonlinear responses of the climate system must have produced these vegetative responses that were even stronger than the solar forcing.