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Science 12 February 1999:
Vol. 283. no. 5404, pp. 971 - 975
DOI: 10.1126/science.283.5404.971
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Reports

A 0.5-Million-Year Record of Millennial-Scale Climate Variability in the North Atlantic

Jerry F. McManus, 1* Delia W. Oppo, 1 James L. Cullen 2

Long, continuous, marine sediment records from the subpolar North Atlantic document the glacial modulation of regional climate instability throughout the past 0.5 million years. Whenever ice sheet size surpasses a critical threshold indicated by the benthic oxygen isotope (delta 18O) value of 3.5 per mil during each of the past five glaciation cycles, indicators of iceberg discharge and sea-surface temperature display dramatically larger amplitudes of millennial-scale variability than when ice sheets are small. Sea-surface temperature oscillations of 1° to 2°C increase in size to approximately 4° to 6°C, and catastrophic iceberg discharges begin alternating repeatedly with brief quiescent intervals. The glacial growth associated with this amplification threshold represents a relatively small departure from the modern ice sheet configuration and sea level. Instability characterizes nearly all observed climate states, with the exception of a limited range of baseline conditions that includes the current Holocene interglacial.

1 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
2 Salem State College, Salem, MA 01970, USA.
*   To whom correspondence should be addressed. E-mail: jmcmanus{at}whoi.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)