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Devilish ice-age record.

With a name like Devils Hole, it's no wonder this flooded fissure in Nevada keeps stoking the flames of discord. Some five years ago, researchers used the climate clues locked within Devils Hole to launch a debate over the cause of the ice ages. Now, the same evidence has come back to haunt them.

Over the millennia, the walls of Devils Hole have become plastered by layer upon layer of calcite, which contains information about rainfall changes in the area. This record first attracted attention in 1988, when scientists studying the calcite reported that the Devils Hole evidence refutes the Milankovitch theory, the standard explanation for the ice ages (SN: 12/3/88, p.356; 10/10/92, p.228).

Named after Yugoslav/an mathematician Milutin Milankovitch, the theory holds that wobbles in Earth's orbit set the pace for the growth and disappearance of the great glacial sheets that have spread over parts of North America, Asia, and Europe every hundred thousand years or so. In the 1970s, research on oxygen isotopes in seafloor sediments provided strong support for the Milankovitch theory.. But scientists who studied Devils Hole suggested that the timing of climate fluctuations recorded in Nevada did not correspond with orbital changes, indicating that some other factor must provide the pacemaker for the ice-age cycle.

Supporters of the Milankovitch theory are now using the Devils Hole record to support the orbital idea. In the June 10 NATURE, John Imbrie of Brown University in Providence, R J. and his colleagues report that the changes recorded at Devils Hole contain hints of cycles lasting 100,000, 40,000, and 23,000 years. These periods match those of the orbital cycles, suggesting that such variations controlled the timing of climate changes at Devils Hole. Imbrie and his co-workers also show that the Devils Hole calcite and the seafloor sediments record inherently different aspects of the climate, which do not change in sync with each other. For that reason, the timing discrepancies between Devils Hole and the orbital shifts need not contradict the Milankovitch theory, they say,
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Title Annotation:data from Devils Hole, NV, supports theory that wobbles in Earth's orbit caused global climate fluctuation
Publication:Science News
Article Type:Brief Article
Date:Jul 17, 1993
Words:345
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