Ice traces of catastrophe: Chernobyl ....Ice traces of catastrophe: Chernobyl . . . Frozen into the earth's ice sheets is a rich history of the changing composition of atmospheric gases, the planetary wind patterns and varying snowfall rates. But to unlock these records, scientists need to know the dates at which layers of ice were created. In this respect, the cloud of the April 1986 Chernobyl nuclear reactor accident had a silver--or rather, a cesium--lining. Cliff I. Davidson at Carnegie-Mellon University in Pittsburgh and his colleagues report in the Aug. 7 SCIENCE that "a well-defined layer of radioactive cesium cesium (sē`zēəm) [Lat.,=bluish gray], a metallic chemical element; symbol Cs; at. no. 55; at. wt. 132.9054; m.p. 28.4°C;; b.p. 669.3°C;; sp. gr. 1.873 at 20°C;; valence +1. is now present in polar glaciers, providing a new reference for estimating snow accumulation rates and dating ice core samples.' Because the Chernobyl cloud extended only into the troposphere troposphere: see atmosphere. troposphere Lowest region of the atmosphere, bounded by the Earth below and the stratosphere above, with the upper boundary being about 6–8 mi (10–13 km) above the Earth's surface. (where, within weeks, particles either fall out or are washed out with precipitation), it left a much clearer signal in the ice than did past nuclear weapons tests, which spewed radioisotopes into the stratosphere stratosphere (străt`əsfēr), second lowest layer of the earth's atmosphere. The level from which it extends outward varies with latitude; it begins c.5 1-2 mi (9 km) above the poles, c.6 or 7 mi (c. where residence times exceed a year. By matching the temperatures at which ice layers form (as determined by the ratios of oxygen isotopes An isotope a type of neutral atom but the number of neutrons is different from the number of protons in the nucleus. May be radioactive. Elements 1-15 Hydrogen
n. The science that deals with the phenomena of the atmosphere, especially weather and weather conditions. [French météorologie, from Greek temperature records, the researchers got a good idea of when and how most of the cesium-137 and cesium-134 arrived on the ice sheet. They also found, with the aid of cesium measurements made elsewhere and with a computer model of wind patterns, that the Chernobyl cloud spread uniformly across North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere. . "That tells us that what we measured in Greenland,' says Davidson, "other scientists are probably going to be able to measure wherever they go in the Arctic.' |
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