Getting Warmer, Cooler, Warmer...

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Science  03 Mar 2000:
Vol. 287, Issue 5458, pp. 1557
DOI: 10.1126/science.287.5458.1557f

The numerous, brief episodes of warming during the last glacial period, initially identified in Greenland ice cores and called Dansgaard-Oeschger (DO) events, are now known to have occurred throughout the Northern Hemisphere. Ocean Drilling Program hole 893A in the Santa Barbara Basin off the coast of California has emerged as a gold mine of information about the marine expression of the DO events that occurred between 60,000 and 25,000 years ago in that region. Using a variety of data from this core, Kennett and colleagues already have uncovered important clues about how the North Pacific ocean behaved during that period by demonstrating that the sediments contain a record of changes in deep-water oxygenation and planktonic foraminiferal oxygen-isotopic compositions. Now, Hendy and Kennett have provided even more detail about those DO events by measuring planktonic foraminiferal species abundances and using these data to calculate sea surface temperatures. Their results show that surface ocean temperatures changed by 3 to 5°C between cool and warm periods and suggest that North Pacific surface circulation was bimodal. These findings support the idea that climate existed near a threshold between two stable states during much of the last glaciation.—HJS

Paleoceanography15, 30 (2000).

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