Statement on the ATOC underwater sound experiment to measure global warming, by project participants Daniel P. Costa (professor of biology) and Stanley M. Flatte (professor of physics), UC Santa Cruz

Contacts: Costa--408/459-2786 or costa@cod.nosc.mil Flatte--408/459-2090 or smf@pacific.ucsc.edu Robert Irion (PIO)--408/459-2495 or irion@ua.ucsc.edu

On April 18, Save Our Shores will hold a panel discussion in Santa Cruz regarding a science program known as Acoustic Thermometry of Ocean Climate (ATOC). As researchers involved with ATOC, we would like to provide perspective on some aspects of the program that have caused confusion and concern.

ATOC will search for evidence of global warming, potentially one of the most serious environmental threats facing our planet. Program scientists will use sound waves to take the temperature of the world's oceans, which store an enormous amount of heat. If global warming is occurring, the ocean will slowly get warmer. Because sound travels faster in warmer water, ATOC could measure this subtle change in just a few years.

Media reports have focused on the sounds that ATOC will produce and their possible effects on marine animals. Unfortunately, most reports have failed to place these issues in a context that would have allowed the public to judge the program fairly. Here are some details that have been overlooked or inadequately explained:

* The sounds will not be "blasts" or explosions. Instead, they will be extremely low-pitched rumblings, such as those made by underwater seismic events. During the 30-month program, ATOC will broadcast these sounds no more than 8 percent of the time.

* The sound source will not be near Monterey Bay or close to shore. Rather, it will be under 3,000 feet of water on Sur Ridge, about 20 miles south of Monterey and 25 miles offshore.

* The most frequently cited intensity of the sounds, 195 decibels, is correct but easily misunderstood for two reasons. First, 195 decibels will be the intensity 3 feet away from the source. Further away, the intensity will drop very rapidly--one hundredth as strong 30 feet away, one ten-thousandth as strong 300 feet away, and so on. Second, decibel levels in water are not the same as those in air. A rock singer producing 110 decibels in air would need to belt out 152 decibels in water to create the same pressures on a listener's ear.

* The source will be no louder than other common sounds in the ocean. Three feet away, its intensity will be similar to that produced by the loudest blue whales or a supertanker. At 300 feet, it will sound no louder than a small freighter. At the surface, the sounds will be about as intense as those made by porpoises. When the sounds reach Monterey Bay, they will fade to the level of natural and constant ocean noise. Only with complex decoding techniques will researchers "hear" the very faint sounds thousands of miles away.

* Because of the source's depth and its location away from biologically rich areas of Monterey Bay, it is extremely unlikely that the sounds will hurt any marine mammals. The only mammals that dive as deep as the source are sperm whales and elephant seals. However, the source will gradually turn on over a 5-minute period, giving animals enough time to swim out of the small zone where the sounds could damage their hearing.

* To look for more subtle effects on mammals such as whales, dolphins, elephant seals, harbor seals, and sea lions, ATOC scientists plan an extensive research program. It will include observing animal behavior, monitoring their underwater communications, and tracking their dives with time-depth recorders and other instruments.

* No effects on marine animals were seen during a test of this experiment near Antarctica in 1991. In that test, the sounds were closer to the surface and much louder.

* The legal language of the federal permit, which discusses "taking" and "harassing" marine animals, has caused unnecessary alarm. These terms simply mean that ATOC might change the behavior of some animals by making them avoid or approach the sounds. In addition, the large numbers of mammals listed in the permit are estimated populations for the entire Pacific Ocean, not just the area near Sur Ridge.

We hope this broader context will encourage a more rational discussion of the merits of ATOC. It is our view that the sounds represent a minor addition to the panoply of natural and artificial noise in the ocean; that the risks to wildlife are remote; and that the promise of valuable information about global warming--which truly threatens a vast range of marine life--is great indeed.

We invite citizens to contact us for more information or to attend the panel discussion, where these issues will be discussed in detail. The discussion begins at 6:30 p.m. on April 18 at the Santa Cruz Yacht Club, 244 4th Avenue.

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