COLUMN ONE : Beneath the Not So Silent Sea : Big ships, oil exploration make the ocean so noisy that some researchers say Big Sur loudspeaker test wouldn’t make much difference. Critics fear whales, other creatures already are at risk.
Forget the notion of the silent deep. The ocean of today is a noisy place filled with the sound of human activity--an aquatic wilderness that is becoming urbanized.
Huge cargo ships make a tremendous subsurface racket; some supertankers are so loud they can be heard underwater a full day before they appear on the horizon.
Along the continental shelf, the rhythmic pounding of seismic air guns used in oil exploration can travel hundreds of miles. Even louder are explosions during offshore construction and naval weapons testing.
“It’s not a silent sea. It’s a cacophony,” said Darlene Ketten, a Harvard Medical School specialist in marine mammals and hearing. “The ocean is a phenomenally noisy environment.”
Commercial, military and scientific use of the ocean has reached such a pitch that some scientists and whale lovers worry that human noise pollution may threaten the well-being of marine life.
A recent proposal to study global warming by repeatedly transmitting a loud, low-frequency rumble across the Pacific Ocean has aroused public concern that the din would disturb whales, dolphins and other animals highly dependent on sound.
Within the scientific community, the experiment has touched off a heated debate over how much ocean noise is too much.
Some scientists say human-made noise could endanger an entire ocean ecosystem that depends on sound, driving animals from their habitats and making it harder for members of a species to locate each other and reproduce.
“This is not a bunch of whale-huggers who are upset about losing a few whales,” said Sylvia Earle, the former chief scientist at the National Oceanic and Atmospheric Administration and a critic of the ocean sound tests. “The issue is a much more profound question of what the impact of large pulses of sound on the ecosystem may be.”
Other scientists, including those who support the global warming experiment, argue that marine animals have adapted well to loud natural sounds--such as underwater volcanoes and cracking polar ice--and would not be unduly disturbed by the loud rumble from the global warming experiment.
“We are a very tiny addition to the background noise created by the international shipping fleet,” contended Andrew Forbes, deputy director of the sound experiment. “We’re not contributing even as much disturbance to the upper ocean as a single ship.”
Between natural and human-made sounds, a constant buzz of background noise drones through most parts of the ocean.
In the quietest regions--areas of the South Pacific where there is little human activity--the typical background noise of wind and waves is 80 decibels. This is about the same as the sound level in the desert on a quiet night. By contrast, many human sources of ocean noise exceed 180 decibels--including supertankers and explosions--a level 10 billion times louder since the decibel scale is geometric.
Underwater, sound is the most efficient means of communication for both man and beasts. Sound travels five times faster in water than in the air and can carry across an entire ocean through what scientists call the deep sound channels--regions about 3,000 feet deep where temperatures and intense pressure combine to guide sound waves over great distances. Navy submarines have long used the sound channels to talk to each other and spy on enemy subs.
“If you’re going to communicate anything in the ocean, you’re going to do it by sound,” said John Potter, a marine acoustics specialist at the Scripps Institution of Oceanography in San Diego. “It’s the natural mechanism for the transfer of information in the ocean.”
Just as people rely primarily on sight, marine creatures depend on hearing to navigate, communicate and hunt. Now, scientists are discovering that some of the largest whales use sophisticated sonar in the same low-frequency range of most noise pollution.
The giant blue whale emits a deep, loud call that can travel great distances through the deep sound channels, bouncing off land masses hundreds of miles away, said Christopher Clark, a Cornell University marine biologist who has been hired to study how the global warming experiment may affect marine mammals. Similarly, he said, finback whales systematically probe their surroundings with rhythmic sound pulses.
But so little is known about these creatures that scientists cannot say for sure how they are affected by the noise of humans, particularly the cumulative effect of low-frequency sounds. No one is certain, for example, how deep most whales dive, what range of frequencies they hear or even how many whales there are.
“This dearth of scientific evidence makes it virtually impossible to predict the effects of low-frequency sound on marine mammals. . . ,” concluded a recent study by the National Research Council, an arm of the National Academy of Sciences.
Underwater explosions, fishing nets and collisions with large ships claim the lives of many marine mammals each year. But Earle and other scientists worry that the effects of ocean noise are more insidious.
Tests done earlier by researchers off Monterey show that migrating gray whales will alter their course to avoid an underwater sound source of 120 decibels or more. Another study indicates that some whales can suffer temporary hearing loss when exposed to sounds as low as 150 decibels.
Supertankers are the largest human-made source of ocean noise, according to the National Research Council study. These ships can produce low-frequency sounds of up to 232 decibels--equivalent in the air to a military jet. Some shipping noise enters the deep sound channels and carries for long distances.
Scott Kraus, associate scientist at the New England Aquarium in Boston, said rising noise levels may help explain why 30% of all right whale deaths in the North Atlantic result from collisions with ships. These slow-moving whales may have become used to the sound of shipping traffic and have difficulty picking out the sound of individual ships bearing down on them until it is too late, he said.
A spokesman for the shipping industry, however, was surprised that anyone was even questioning vessel noise.
“What do they want, no ships in the ocean?” asked Ernest Corrado, president of the American Institute of Maritime Shipping, which represents most of the nation’s major shipping companies. “We have water pollution, air pollution--the latest thing was our ballast water. Noise pollution? That’s a whole new one.”
Even louder than individual supertankers are the seismic exploration ships that search for oil deposits by firing air guns every 10 or 20 seconds at the ocean floor. The guns, which simultaneously release bursts of air bubbles, can reach 240 decibels.
Scientists who monitor acoustic activity in the ocean with hydrophones say they can hear the repeated firing of air guns as far as 500 miles away. “Frankly, that would drive me nuts,” said Potter, who has spent many research hours listening to the air guns booming away.
Oil industry officials, however, say studies have found no evidence the noise harms marine life. Whales that don’t like the sound can avoid areas where survey ships are operating, said Jeff Wilson, a spokesman for the Western States Petroleum Assn. Air guns, he noted, are an improvement over the days when dynamite was used.
“There is no evidence that air guns used in marine geophysical surveys injure or disturb whales,” he said.
One of the loudest ocean noises is the sound of blasting during construction of piers and other marine facilities. In 1992, at least two humpback whales off Newfoundland were killed in an explosion during pier construction. Ketten, the Harvard expert, examined the whales after they became entangled in fishing nets and found they had suffered from severe ear trauma, including shredded eardrums and crushed ear bones, that would have deafened them.
Scientists also said the explosions--later calculated to have reached 296 decibels--may have caused other humpback whales to suffer hearing loss, impairing their ability to detect obstacles; after the blasting began, fishermen in the area noticed a sudden increase in the number of humpbacks snared in their nets.
A 1972 federal law designed to protect marine mammals requires the National Marine Fisheries Service to issue permits for the incidental harassment of whales. But the Navy, shipping and commercial fishing are largely exempt from the requirement.
Since World War II, the Navy has conducted weapons tests--such as ship shock tests off the Channel Islands National Marine Sanctuary using 10,000-pound bombs--and high-decibel acoustic experiments in the ocean under a cloak of secrecy.
Only now, with the end of the Cold War and a growing emphasis on research for civilian purposes, are such tests becoming public. The global warming experiment is one of the first to go through the process of obtaining a federal permit for harassment of marine mammals.
The controversial plan to take the ocean’s temperature with underwater sound waves is the brainchild of Walter Munk, one of the world’s leading physical oceanographers.
Now 75, he has worked with the Navy on and off since World War II, when he correctly predicted the magnitude of waves for Allied invasions of North Africa and Normandy. Later, he assisted the Navy by analyzing how Bikini Island nuclear weapons tests affected the ocean.
For more than a decade, Munk has worked on mapping the sea through acoustic tomography--a sort of ocean CAT scan using 185-decibel sounds transmitted over distances of 600 miles to learn about temperature, tides and currents.
Munk, based at Scripps Institution of Oceanography, said he developed the idea of using sound to study ocean temperatures after hearing how a scientist dropped dynamite into the ocean near Australia and picked up sound of the explosion off Bermuda. “Using sound in the ocean, if done properly, is a most powerful tool,” he said.
Since sound travels faster in warmer water, Munk hopes to measure average deep sea temperature changes of as little as one five-thousandth of a degree across the Pacific basin. If the study shows the thermometer rising, he said, it could provide clear evidence of global warming and help governments plan how to reduce the atmospheric carbon gases believed responsible.
The initial $35-million, two-year experiment is sponsored by the Defense Department, which will have access to all the data for military use, such as improving submarine surveillance.
Munk and his colleagues have applied for federal permits to place loudspeakers about 3,000 feet deep on the ocean floor off Big Sur and the Hawaiian island of Kauai. These would transmit low-frequency, coded signals of up to 195 decibels across the Pacific. A hearing on the California permit is set for May 16 in Santa Cruz.
Although the speakers might not be as loud as air guns or some supertankers, test sponsors acknowledge they would produce the dominant human-made sound in the regions where they are placed--the Monterey Bay National Marine Sanctuary and a breeding area for humpback whales off Hawaii.
Munk said he has tried to use the softest noise possible, noting the signal would be so faint when it reaches New Zealand it must be plucked out of the background noise by high-tech Navy listening gear.
Scientists agree that any effect on animals will occur near the loudspeakers.
Within about 500 feet of the speakers, project scientists estimate, the sound will remain at 150 decibels or above, potentially loud enough to cause temporary hearing loss in some whales. But they say it is highly unlikely any animals would stay within that range long enough to affect their hearing.
For 18 miles in all directions, however, the volume would be at least 120 decibels--the level known to produce an aversion response among gray whales.
Off Big Sur, the oceanographers estimate that as many as 677,000 marine mammals, including a number of endangered species, live in or would pass through that circle of sound and could be disturbed by the noise.
As part of the experiment, Munk has brought in leading marine mammal researchers to see how the noise affects key indicator species, such as humpback whales and the deep-diving elephant seal.
Researchers will monitor a sample of these animals from land and from airplanes at least 1,000 feet above the water. They want to see if the creatures alter their behavior when the sound is on.
Clark, the Cornell marine biologist, insists the animal-watchers will be able to determine whether the sound is disruptive. And Munk promises to halt or modify the test if they discover the noise is harming animals.
But opponents say the effort is flawed because insufficient data has been gathered ahead of time about the normal behavior of these species. And, they say, it will be hard to see from the air or the coast what effect the noise has on creatures that spend their lives underwater.
As an alternative, some critics have called for non-invasive methods of measuring ocean temperatures, such as using large numbers of thermometers that could be monitored by satellite. At the very least, they say, the loudspeakers should be moved to locations with fewer marine mammals and endangered species.
“To those who say it doesn’t matter, I say it matters to all of us,” Earle said. “The ocean is being subjected to many stresses. We don’t know what the outcome of our actions may be on the ocean ecosystem, but it is not likely to be in our best interest to disrupt things unnecessarily.”
Sounding Off
Some scientists worry that the addition of new human noises to the ocean may disturb marine creatures that are highly dependent on sound. Because scientists use different starting points to measure sound in water and in air, the decibel scale for underwater sound begins at 61.5 decibels, instead of zero. The decibel scale is geometric, so an increase of 10 decibels signifies a sound that is 10 times louder, an increase of of 20 is 100 times louder. Here are some typical peak levels for low-frequency sound sources in the ocean:
Background noise in quiet ocean far from shipping: 80 db
Background noise in ccoastal region near shipping: 105 db
The point at which a whale would head away from the sound: 120 db
Small motorboat: 135 db
Ice noises in polar region: 140-155 db
Whale vocalizations: 150-195 db
The global warming sound test loudspeaker: 195 db
Geophysical phenomena (earthquakes, volcanoes): 160-240 db
Large ships and supertankers: 170-230 db
Large underwater explosion: 250-295 db
Source: Scripps Institution of Oceanography.
