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Global quick-freeze.

Global quick-freeze

Accumulating evidence suggests that Earth's climate did a giant double-take as it thawed from the last ice age, a time when huge clacial sheets covered parts of North America, Europe and Asia. After an initial warming beginning about 15,000 years ago, the entire globe apparently slipped back into a temporary cold spell called the Younger Dryas period that started about 11,000 years ago and ended 1,000 years later.

Climate experts have long thought the Younger Dryas cooling affected only the North Atlantic region, and they have suggested various mechanisms to explain such a regional cooling. But recent evidence from other parts of the globe indicates that the entire world underwent some sort of climate shift during the Younger Dryas. The finding forces scientists to consider a global explanation for the geologically quick chill, say German researchers who report the new data in the Jan. 31 NATURE.

The team found evidence for worldwide changes in sediment cores collected from the Sulu Sea, which lies between the Philippines and Borneo. Measurements of oxygen isotopes in the cores reveal that the surface waters of the Sulu Sea slipped back toward ice age conditions sometime around 10,800 or 11,065 years ago. The isotope shifts suggest the water in this area cooled by 3[degrees]C or became less salty, or both. At around the same time, cool-water plankton species populated this subtropical region.

The evidence from the Sulu Sea fits with other recent findings from the Gulf of Mexico, the North Pacific Ocean and Argentina. As an explanation for the apparently worldwide changes, the German researchers suggest a reverse greenhouse effect caused by a drop in the atmosphere's carbon dioxide concentrations. A slowdown in the melting of the glacial ice caps could have stimulated plant growth in the oceans, which in turn would have absorbed carbon dioxide from the atmosphere, they propose.
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Title Annotation:Earth's climate at the time of the last ice age
Publication:Science News
Date:Feb 9, 1991
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