Ocean Researchers Seek to Alter Sound Experiment

Scientists investigating global warming by broadcasting sound beneath the ocean want to temporarily modify the experiment to make it more efficient.

The researchers, based at the Scripps Institute of Oceanography in La Jolla, want to change the frequency of the low rumbles they transmit 50 miles off Half Moon Bay.

Peter Worcester, lead investigator for the Acoustic Thermometry of Ocean Climate Project, said that if the lower sounds travel more efficiently to receivers thousands of miles away, fewer transmissions may be needed. That would be less bothersome to ocean life.

But Mark Delaplaine, a staff member of the California Coastal Commission, which must approve the change, said there is some concern that the lower frequency would be more disruptive to whales than the higher one.

Researchers have been broadcasting sound from a location 3,200 feet below the surface since December. The sound, about as loud as an ambulance siren, is turned on for 20 minutes every four hours for a period of four days, then switched off for two days.

Scientists are looking for changes in the speed the sound travels across the Pacific. Because sound moves faster in warm water, changes in the speed over time could indicate that the planet is warming.

Researchers propose to turn off the transmitter for two weeks in June and transmit a lower-frequency sound from an instrument dangled from a ship in the same area. They want to lower the frequency to 25 hertz from 75 hertz.

Delaplaine said some people also worry that a change of only two weeks would disrupt the experiment and not provide enough information about the lower frequency.