BOSTON — 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 the entire sea has operated for eons.
Based on volume of traffic alone, scientists know the North Atlantic and North
Pacific oceans, which are the busiest, are also the noisiest, said Christopher
Clark, a Cornell bioacoustics scientist. The area around Indonesia is heavy too
with shipping traffic.
Clark, who monitored Cape Cod Bay with underwater listening devices, found the
ocean flat and the winter darkness unbroken by ship lights. But below the bay's
surface, 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.
The sound carrying through the bay that evening was part of an ever louder
man-made din that's filling the world's oceans, and some say harming marine
life.
Hearing is the primary sense for marine life, which uses sound for navigation
and communication. Some scientists believe 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 completely 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 is 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, which is created when molecules collide, carries farther and five times
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.
Through the ages, 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 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's convincing evidence of a phenomenon called
"masking," in which the increased ambient noise drowns out natural
ocean communications.
Huge increases in commercial shipping have coincided with increased ocean noise.
Between 1948 and 1998, the world 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
roughly 15 decibels in that time.
Joel Reynolds, director of the Marine Mammal Program at the Natural Resources
Defense Council, said there's evidence marine mammals are changing their sound
patterns or rates, which could show their normal communication has been
disrupted.
Kathy Metcalf, director of Maritime Affairs at the Chamber of Shipping in
America, said she concedes that increasing ocean noise caused by ships will at
some point interfere with marine life. Metcalf advocates pre-emptive steps, such
as installing quieter propellers in new ships, which would reduce noise and
likely benefit the industry by increasing the efficiency with which ships move
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. "There's a huge issue surrounding the validity of
the science on this issue."
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 added that sound is perceived by ocean animals so differently than land
animals that it's almost like a different sense, making it hard to apply what we
know about the effects of certain decibel levels to ocean life.
Still, Southall said he's optimistic that the emerging interest in the topic
will lead to breakthroughs.
Reynolds said regulating ocean sound doesn't mean ending all its benefits,
whether it's better national defense or the robust trade that comes with heavy
shipping.
"We have to treat it like any other form of pollution," Reynolds said.
"We have to regulate it to protect other things we care about."
Clark said uncertainties can't be an excuse to do nothing, because the damage
might be done by the time the effects of noisy oceans are known.
"It's like global warming," he said. "We're going to get one
chance."
Source: Associated Press