January 13, 1997

UCSC researchers speak at Acoustical Society meeting

By Robert Irion

Several marine biologists and physicists from UCSC spoke at a recent joint meeting of the Acoustical Society of America and the Acoustical Society of Japan, held in Honolulu, Hawaii, from November 30 through December 3. A highlight of the meeting was a session on results from the first year of data taken by the Acoustic Thermometry of Ocean Climate (ATOC) experiment, an effort involving many oceanographic institutions around the world, including UCSC.

ATOC scientists hope to detect changes in the temperature of the world's oceans by transmitting low-frequency sound waves through the sea and measuring the faint signals with sensitive equipment. Even a subtle change in water temperature would affect the speeds at which these sound waves travel. If the water warms slightly, perhaps due to the effects of global warming, sounds will move more quickly from one side of the ocean basin to the other.

When ATOC was first proposed, environmental groups expressed concern that the sound transmissions might affect marine mammals near the transmitters. As a result, ATOC now includes a substantial marine-mammal monitoring program for its transmission sites off California and Hawaii. UCSC professor of biology Daniel Costa heads this program for the California site, 50 miles offshore from Half Moon Bay.

At the Hawaii meeting, Costa and other UCSC researchers--including professor of physics Stanley Flatté, research professor of biology Burney Le Boeuf, and several postdoctoral researchers and graduate students--described their observations of seasonal temperature changes, ocean internal waves, and the effects of sound on marine mammals. According to observations by Costa's team to date, the sounds have had no significant effect on sperm whales, gray whales, humpback whales, or elephant seals.

Members of the public were invited to comment on the marine-mammal results at an open forum. However, no comments from environmental groups were presented.

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