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Sound sent halfway around the world.

Sound sent halfway around the world

After traveling 18,000 kilometers through the deep ocean, sound signals transmitted near Antarctica arrive, faint but clear, at the East and West coasts of North America. The successful experiment raises hopes that scientists can use this technique over the next decade to gauge whether the expected greenhouse warming has started.

U.S. and Australian researchers tested the idea in late January during a trial experiment near remote Heard Island in the Antarctic Ocean. An underwater transmitter emitted periodic signals about as loud as a foghorn, and 17 receiving stations around the globe listened for the weak sound (SN: 1/26/91, p.53). Scientists hope to use the timing of the signal's arrival to make precise measurements of the speed of the sound, and then monitor future transmissions for any change in speed. A widespread increase in the sound speed over several years would indicate an oceanic warming.

Project coordinator Robert Spindel, an engineer with the University of Washington in Seattle, says almost all the listening stations picked up the signal. The sound took about 3.5 hours to reach its most distant destinations, the North American stations. The researchers are now conducting tests to determine whether the received signals came in clearly enough to allow a sufficiently accurate measurement of the sound speed. "It looks like the answer is yes," Spindel says.

Spindel and his colleagues hope to install the first of several permanent underwater transmitters in 1993, and then add several more transmitters around the globe as part of a long-term monitoring program. Because various ocean regions will respond differently to climate change, the researchers will need widespread coverage to catch signs of a global warning.
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Title Annotation:experiment in sending sound waves through the ocean as a means of gauging greenhouse warming
Publication:Science News
Date:Apr 6, 1991
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