A $40 million research program has proved that sound can be used to measure the temperature of the world's oceans and detect long-term climate change, scientists say. But the project has spent so much money meeting demands by environmental groups that its leaders expect to have to end the program a year from now.
The experiment, called Acoustic Thermometry of Ocean Climate (or "ATOC," pronounced "aye-tock,") is based on precise measurements of the speed of sound through oceans; the warmer the water, the faster sound travels. The ATOC consortium, comprising research teams from eight institutions in the United States and Australia, published a summary of its results in a recent issue of the journal Science.
The experiment initially aroused strong opposition from the wildlife lobby and several environmental organizations on grounds that the sounds generated by underwater loudspeakers used in the tests would disturb wildlife, alter animal behavior and perhaps endanger whales and other marine animals. The ATOC physicists and acoustics experts argued that the low rumbling sound they planned to propagate into the water in short occasional pulses was no louder than the sound of passing ships and only slightly louder than the calls of blue whales to one another.
From the outset, project scientists agreed that it was important to protect wildlife but would not accede to some of the demands by the various groups. Finally in 1995, after spending $2.9 million from its acoustic research budget on animal studies and legal expenses, ATOC began its experiment, as modified to comply with the demands of the lobbyists.
"The loss of all that money so weakened us that we expect to have to end our work one year from now when our funding runs out," said Dr. Walter Munk of the Scripps Institution of Oceanography at La Jolla, Calif., a senior scientist with the project. "Because of the many delays and legal costs," he said, "we've only been able to collect a year and a half's worth of data -- too little to detect global warming from a greenhouse effect. We would need a decade of data to see it. It's very sad to have to stop at this stage."
The ATOC collaboration contends its experiment would have had to have run for at least 10 years to detect global greenhouse warming unequivocally -- a goal they say would have been attainable if they had been spared the expenses of meeting demands by lobbyists.
The ATOC project has been supported since 1990 by research institutions in eight nations and the National Academy of Sciences, the Office of Naval Research, the National Oceanic and Atmospheric Administration and various universities.
Sound can travel through water for enormous distances, prevented from dissipating its acoustic energy by boundaries in the ocean created by water layers of differing temperatures and densities. In the final version of the experiment, loudspeakers were installed at two sites: one off the northwest coast of Hawaii's Big Island, and the other near Pioneer Seamount, a volcanic island in the Pacific Ocean 55 miles from San Francisco. The times of arrival of the sound at thousands of underwater microphones spanning the Pacific Ocean were then recorded and interpreted as water temperatures.
The advantage of the ATOC system over traditional arrays of thermometers on buoys and ships is that it takes an integrated measurement of temperature all along the path the sound takes, averaging the temperatures of water over thousands of miles. Systems reliant on spot temperatures fail to collect enough data from regions of the oceans sparsely covered by sensors of any kind.
Another method of measuring oceanic heat is used by a French-American radar satellite named Topex/Poseidon, which can detect changes in sea level of as little as a few inches. Changes in sea level result not only from changes in water temperature (and therefore its density) and but from the melting of glaciers. Satellite measurements alone cannot distinguish between these effects.
But when data from the ATOC array is combined with radar sea level measurements, it is possible to calculate exactly how much of an increase in sea level is attributable to the warming of water alone, and over a period of years, such measurements can reveal a global warming of the seas by a warming atmosphere.
No other technique has been discovered that can yield this global-scale information with such accuracy, the investigators say. Moreover, data combined from satellite sea level measurements and ATOC-type speed-of-sound measurements are expected to greatly improve mathematical models simulating the behavior of the earth's climate.
Although the debate over the effects of the project's sounds on marine animals persists, biologists who conducted tests reported that effects were apparently not injurious.
Dr. Adam S. Frankel of Cornell University, a biologist who specializes in acoustics, was one of the scientists commissioned by the consortium to monitor the effects of the project's sound on humpback whales. These whales were considered especially sensitive to the pitch of the ATOC sound, which has a rumbling frequency of 75 hertz (cycles per second). Humpback whales communicate using sounds that low, but dolphins and many other animals can hear only higher-pitch sounds.
Dr. Frankel and his colleagues reported the results of their investigation in a recent issue of the Canadian Journal of Zoology.
From a hill on the island off San Francisco the biologists observed the surface behavior of the whales in 84 trials. In most of them, the whales were exposed to sound from the ATOC loudspeaker or engine noise from passing ships, while in others, for comparison, the whales were exposed to no man-made noises.
"We looked for changes in swimming speeds and directions, and other behavioral changes, including respiration," Dr. Frankel said. Respiration rate can be measured by the intervals between blowing.
"We saw no breaching or swimming in unison -- both indicators of distress in whales," he said. But some changes in diving were observed, he said, particularly when the noise was coming from a ship's engines. Exposure to sound seemed to be associated with dives that were longer in duration and distance.
"Overall," Dr. Frankel said, "I wouldn't call the ATOC sound benign, but its effects seem to be small -- perhaps an annoyance to the animals rather than a hazard."
Dr. Rod Fujita, a marine biologist and spokesman for the Environmental Defense Fund, one of the organizations that opposed the acoustic thermometry program, said he was not convinced by the results that Dr. Frankel reported.
"I wouldn't change my mind on the basis of a single publication, and we have yet to hear from the advisory panel on biology convened by ATOC," he said. "The impacts of sound on wildlife are subtle, and gauging them is somewhat subjective. While ATOC would be helpful in calibrating models of climate change, it's not the be-all and end-all of climate measurement. The important thing is to take immediate steps to curb global warming."
If the program is to be ended anyway, does it matter that many biologists now regard its sound pulses as harmless to wildlife?
"The question is not moot," Dr. Frankel said. "ATOC may be dead, but the technique it developed and tested is very much alive. The world still needs to know whether greenhouse warming and climate change are occurring, and this is a useful indicator."
GRAPHIC: Diagram: "Sounding It Out"
To gauge average water temperature, researchers are working on an experiment called Acousto. Thermometry of ocean climate (ATOG) are measuring the speed of sound across exparees of ocean. Because sound travels faster in warm water than cold, the time it takes a signal to reach it's destination indicates the water's temperature. Diagram illustrates the technology. (Source: ATOC)
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