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Getting to the core of climate cycles.

At the coldest inhabited spot on the planet, Soviet engineers have drilled 2,083 meters into the ice, obtaining the first continuous ice record of the drastic swings in climate over the last 150,000 years. The high-quality core they have extracted from the Vostok station in East Antarctica extends from the present interglacial, or warming, period through about 100,000 years of glacial cooling, then on through the previous interglacial episode and into the tail end of another glaciation.

Soviet and French researchers collaborating in the analysis of the core present some of their initial geochemical results in two papers in the Aug. 15 NATURE. In one paper, Claude Lorious of the Laboratory of Glaciology and Environmental Geophysics in St. Martin d'Heres, France, and his co-workers measured the changes in the abundance of the oxygen-18, they believe, is linked to the temperature of East Antarctica, with increases of the isotope reflecting a warmer climate. And since temperature is thought to affect the accumulation rate of the ice, oxygen-18 measurements enabled them to date the ice as well.

The measurements revealed three relatively cold periods within the last glacial episode. The researchers found that the last interglacial period was warmer, perhaps by 3 [deg.] C, than the present period. They calculate temperature differences of about 10 [deg.] C between glacial and interglacial times.

One very striking feature of the oxygen-18 profile is how clearly it follows a 40,000-year cycle in insolation, the amount of solar radiation that reaches the earth's surface. This strongly supports the idea that periodic variations in insolation -- brought on by cyclic changes in the earth's orbit--contribute to local climate shifts. The oxygen-18 results are also consistent with other studies that estimated changes in carbon dioxide levels--another factor linked to climate. But the results do not agree with oxygen-18 studies of deep-sea cores, indicating to the researchers that the Antarctic climate and the global volume, which the deep-sea cores are thought to reflect, have not evolved in the same way. In particular, they say, "The last interglacial appears to be about twice as long as in the Antarctic temperature record as in the ice-volume record."

The oxygen-18 ice data also correlate very well with measurements of beryllium-10 discussed in the second NATURE paper, written by F. Yiou at the Rene Bernas Laboratory in Orsay, France, and colleagues. These researchers link beryllium levels to the precipitation rate, which, they conclude, was two times lower during the last glaciation than in the interglacial periods.
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Title Annotation:Soviet engineers obtain ice core recording swings in climate over last 150,000 years
Publication:Science News
Date:Aug 31, 1985
Words:416
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