‘Acoustic Smog’ Taking a Noisy Toll on Ocean’s Quiet
The ocean was flat and the winter darkness over Cape Cod Bay was unbroken by ship lights. But below the bay’s surface, Christopher Clark found things weren’t as serene as they seemed.
The bay is saturated with sound.
“It’s just a great big amphitheater,” said Clark, a Cornell bioacoustics scientist who monitored the bay with underwater listening devices.
The sound carrying through the bay that night was part of an ever-louder man-made din that’s filling the world’s oceans, and some say harming marine life.
High-profile whale beachings have been linked to sonar blasts and sparked fierce public debate over the military’s use of sound in national defense. But a broader concern for scientists is rising levels of ocean background noise, much of it generated by commercial shipping, and whether it interferes with the way that the entire sea has operated for eons.
Based on volume of traffic alone, scientists know that the North Atlantic and North Pacific oceans, which are the busiest, are the noisiest, Clark said. The area around Indonesia also is heavy with shipping traffic.
Hearing is the primary sense for marine life, which uses sound for navigation and communication. Some scientists think that the spreading “acoustic smog” is essentially blinding marine life, affecting feeding, breeding and other crucial activities.
“Their world is just being collapsed,” Clark said. “They rely so heavily on sound. They can’t see anything.”
Despite concerns, evidence is scant of the real effects of sound.
Even with new technology, ocean animals are hard to track, and drawing conclusions about how sound influences their behavior is difficult. No system exists to monitor ocean sounds worldwide, and the data that’s collected is often taken from a small number of sites that measure only certain frequencies. Underwater sound also seems to affect different animals in different ways.
Businesses and the military are unlikely to make major changes before more is known.
Brandon Southall, an acoustics researcher at the National Oceanic & Atmospheric Administration, said better research was urgently needed. “People are inherently tied to the ocean for food, for cures to diseases, for weather,” he said. “We’re figuring out things are more interconnected than we ever could have originally envisioned.”
Sound, created when molecules collide, carries farther and faster in water than air because of water’s density. Since molecules in water are spaced closer together, they lose less energy before colliding with other molecules, and sound is transferred more quickly and efficiently.
Over time, marine animals have learned to take advantage of the ocean’s natural sound stages. Whales, for instance, talk about basic things like where the best food or breeding is. They even seem to compete to produce the most intricate songs.
Researchers believe that animals may use the ocean’s natural “sound channels” to communicate over thousands of miles. The channel is created where dropping temperatures, which force sound waves downward, meet increasing water pressure, which forces sound waves upward. At a certain depth, the sound gets caught between the two opposing forces and bounds ahead with little resistance.
Researchers suspect that dumping a cacophony of new noise into this system isn’t good. Southall said there was evidence of “masking,” where increased ambient noise drowned out natural ocean communications.
Huge increases in commercial shipping have coincided with increased ocean noise. Between 1948 and 1998, the world’s shipping fleet has increased from 85 million tons worth of ship weight to 550 million tons, according to figures in a 2003 report, “Ocean Noise and Marine Mammals,” published by the National Academies. Scientists say the background noise in the ocean has increased about 15 decibels in that time.
Joel Reynolds, Marine Mammal Program director at the Natural Resources Defense Council, said there was evidence marine mammals were changing their sound patterns, which could show that normal communication had been disrupted.
Kathy Metcalf, maritime affairs director at the Chamber of Shipping in America, conceded that increasing ocean noise caused by ships would at some point interfere with marine life. She advocated installing quieter propellers in new ships, which would reduce noise and likely benefit the industry by increasing the efficiency with which ships moved through water.
But retrofitting current ships to reduce noise would be extremely expensive and the benefit is uncertain, she said.
“If somebody is going to signal we need to start absorbing these costs when we’re not even sure there’s a negative impact, that’s where we’re digging in our heels,” she said.
Southall acknowledges the mountain of work ahead to come up with real answers about ocean noise. To illustrate the difficulties of applying the science to ocean life, he points to the beluga whale, which flees from ship sounds in the high Arctic, but moves toward certain vessels in Alaska.
He said that sound was perceived by ocean animals so differently than land animals that it was almost like a different sense, making it hard to apply what we knew about the effects of certain decibel levels to ocean life.
Still, Southall said he was optimistic that the emerging interest in the topic would lead to breakthroughs.
Reynolds said regulating ocean sound didn’t mean ending all its benefits, whether it was better national defense or the robust trade that came with heavy shipping.
“We have to treat it like any other form of pollution,” he said. “We have to regulate it to protect other things we care about.”
Clark said uncertainties couldn’t be an excuse to do nothing because the damage might be done by the time the effects of noisy oceans were known. “It’s like global warming. We’re going to get one chance.”
