Reassessing Rapid Variations

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Science  05 Oct 2001:
Vol. 294, Issue 5540, pp. 15-17
DOI: 10.1126/science.294.5540.15e

Millennial-scale episodes of rapid climate change occurred throughout much of the latter part of the Pleistocene. These oscillations generally occurred with greater regularity and intensity during glacial periods, which are characterized by the greater volume of the large continental ice sheets. Whether the oscillations depend on other factors, such as insolation, is a question that climatologists have asked since the discovery of these cycles.

McIntyre et al. present North Atlantic sedimentary records from the late Pliocene to the early Pleistocene, with ages between 1.93 and 1.75 million years ago. During this period, maximum ice volumes were only one-third to one-half as large as during the late Pleistocene, and glacial cycles occurred every 41,000 years instead of every 100,000 years. Nevertheless, the patterns of iceberg formation and deep-water circulation that existed then share many characteristics with those of more recent records. These findings suggest that the oscillations also are controlled by forcing external to the ice sheets themselves and not just by internal ice sheet dynamics or by the strongly nonlinear interaction between climate and solar forcing that results from the presence of large ice sheets that form during 100,000-year-long glacial cycles.—HJS

Paleoceanography16, 535 (2001).

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