Global warming experiment shifts focus to marine mammals

In 1994, conservationists raised a big ruckus about the danger of a sound experiment called ATOC, which is now underway. But how loud is ATOC, really?

Even though U.S. law should protect many marine species from noise pollution, few people worried about the issue of ocean noise until 1993, when a team of oceanographers led by Walter Munk of the Scripps Institution of Oceanography in La Jolla, California, proposed the ATOC experiment (Acoustic Thermometry of Ocean Climate). Munk and his colleagues planned to install a low-pitched rumbling sound source on the ocean floor off California, and measure how quickly its sound moved across the Pacific Ocean. Sound travels faster in warmer water. So, after a few years measurement, if ATOC sounds were traveling faster, the researchers could conclude that the ocean, and presumably the rest of the earth, was getting warmer.

Environmentalists railed against the proposal, mainly because of estimates that the 195 dB pulses (that's louder than a jet engine) could affect as many as 2 million animals. ATOC scientists responded by designing a preliminary experiment to examine how ATOC sounds might affect marine mammals. The federal government approved the plan, and in December 1995 scientists turned on the ATOC source: one 20-minute pulse every four hours for two days at a time. The ATOC research group at the University of California, Santa Cruz, lead by biology professor Dan Costa, has ventured out in boats and planes, looking for behavior changes in marine life near the sound source. So far, the researchers report almost no effect.

Most oceanographers and biologists now agree that what we stand to learn from the ATOC marine mammals justifies whatever harm the experiment might cause. This is especially true given that ATOC sounds are not that loud compared to other man-made ocean noises. "ATOC is a really loud noise, but in terms of a lot of other noises, it's not that big of a disturbance," says Darlene Ketten, an assistant professor at Harvard Medical School who studies whale hearing.