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Historical coral.

Historical coral

In recent years, scientists have sought to decipher the mechanisms behind the El Nino-Southern Oscillation (ENSO) events--12- to 18-month-long periods of climatic havoc in the Pacific that bring drought to Australia and floods to Ecuador and other countries along the eastern Pacific. Although no pattern of ENSO events has yet emerged, researchers cannot be sure whether long-period cycles exist because they lack data for times in the distant past. For example, merchant marine measurements of Pacific sea-surface temperatures and wind go only as far back as the 1840s and are often unreliable.

Those in search of a pattern, therefore, are turning to more long-term records of climate patterns, such as snow accumulation rates atop Peruvian mountains and sediment layers off Baja California. Now, Glen T. Shen of the Lamont-Doherty Geological Observatory in Palisades, N.Y., suggests that scientists can use cadmium levels in coral from the Galapagos Islands to trace an important factor in weather--the vertical movement of water--over periods of several hundred years.

While cadmium is usually depleted in the surface layers of the ocean, in certain areas, such as the eastern Pacific, water from the deep ocean rises and replenishes the nutrients and cadmium levels of the upper ocean. The coral near the Galapagos then incorporates cadmium into its shell as it grows at a rate of up to 2 centimeters a year. During ENSO events, however, wind shifts depress this upwelling and cadmium levels drop in the upper ocean--a change that is recorded within the coral's shell, reports Shen in the Aug. 27 NATURE. Coral records will help reveal any long cycles and in turn might illuminate certain causes of ENSOs, says Shen, who is now working on a coral that started growing in 1583.
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Title Annotation:use of cadmium levels in coral to track vertical movement of water over time
Publication:Science News
Date:Sep 12, 1987
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