When a hurricane forced the Nautilus to dive in Jules Verne’s “Twenty Thousand Leagues Under the Sea,” Captain Nemo took the submarine down to a depth of 25 fathoms, or 150 feet. There, to the amazement of the novel’s protagonist, Prof. Pierre Aronnax, no whisper of the howling turmoil could be heard.
Multimedia
Cacophony in the Deep
This week, we look at an increasingly noisy ocean with examples from the "Discovery of Sound in the Sea" project.How loud is it in the ocean?
-
Humpback Whale
-
Beluga Whale
-
Earthquake
-
Surveillance Towed Array Sensor System Low Frequency Active Sonar
-
Large Commercial Ship
Like the science desk on Facebook.
“What quiet, what silence, what peace!” he exclaimed.
That was 1870.
Today — to the dismay of whale lovers and friends of marine mammals, if
not divers and submarine captains — the ocean depths have become a noisy
place.
The causes are human: the sonar blasts of military exercises, the booms from air guns used in oil
and gas exploration, and the whine from fleets of commercial ships that
relentlessly crisscross the global seas. Nature has its own undersea
noises. But the new ones are loud and ubiquitous.
Marine experts say the rising clamor is particularly dangerous to
whales, which depend on their acute hearing to locate food and one
another.
To fight the din, the federal government is completing the first phase
of what could become one of the world’s largest efforts to curb the
noise pollution and return the sprawling ecosystem to a quieter state.
The project, by the National Oceanic and Atmospheric Administration,
seeks to document human-made noises in the ocean and transform the
results into the world’s first large sound maps. The ocean
visualizations use bright colors to symbolize the sounds radiating out
through the oceanic depths, frequently over distances of hundreds of
miles.
It is no small ambition: the sea covers more than 70 percent of the
planet’s surface. But scores of the ocean visualizations have now been
made public.
Several of the larger maps present the sound data in annual averages —
demonstrating how ages in which humans made virtually no contribution to
ocean noise are giving way to civilization’s roar.
The project’s goal is to better understand the cacophony’s nature and
its impact on sea mammals as a way to build the case for reductions.
“It’s a first step,” Leila T. Hatch, a marine biologist and one of the
project’s two directors, said of the sound maps. “No one’s ever done it
on this scale.”
The began the effort in 2010 at the behest of Jane Lubchenco, a
prominent marine biologist who is the first woman to head the agency.
Dr. Hatch and her colleagues assembled a team of sound experts,
including HLS Research, a consulting firm in La Jolla, Calif. This
summer, they unveiled their results
on the Web, as did a separate team of specialists that sought to map
the whereabouts of populations of whales, dolphins and porpoises.
Michael Jasny, a senior policy analyst with the Natural Resources
Defense Council, a private group in New York that has sued the Navy to
reduce sounds that can harm marine mammals, praised the maps as
“magnificent” and their depictions of sound pollution as “incredibly
disturbing.”
“We’ve been blind to it,” Mr. Jasny said in an interview. “The maps are
enabling scientists, regulators and the public to visualize the problem.
Once you see the pictures, the serious risk that ocean noise poses to
the very fabric of marine life becomes impossible to ignore.”
Legal experts say the new findings are likely to accelerate efforts both
domestically and internationally to deal with the complicated problem
through laws, regulations, treaties and voluntary noise reductions.
The government already has some authority to regulate oceanic sound in
United States waters through the Endangered Species Act and the Marine
Mammal Protection Act, though exemptions to these laws exist for the
military.
The International Maritime Organization, a United Nations body
responsible for improving marine safety and reducing ship pollution,
also has the authority to set acoustic standards. In the past few years,
encouraged by the United States, it began discussing how to achieve
voluntary noise reductions.
Since many commercial vessels are registered abroad, and most shipping
noises arise in international waters, the organization’s backing is seen
as crucial for reductions to be substantial enough to have global
repercussions.
“Right now we’re talking about nonbinding guidelines,” said Michael
Bahtiarian, an adviser to the United States delegation to the maritime
organization and a senior official at Noise Control Engineering, a
company outside Boston that specializes in reducing ship noise and
vibrations. “At a minimum, the goal is to stop the increases.”
Multimedia
Cacophony in the Deep
This week, we look at an increasingly noisy ocean with examples from the "Discovery of Sound in the Sea" project.How loud is it in the ocean?
-
Humpback Whale
-
Beluga Whale
-
Earthquake
-
Surveillance Towed Array Sensor System Low Frequency Active Sonar
-
Large Commercial Ship
Related
Times Topic: Sonar
The oceanic roar originates because of the remarkable — and highly
selective — way in which different kinds of waves propagate through
seawater. While sunlight can penetrate no more than a few hundred feet,
sound waves can travel for hundreds of miles before diminishing to
nothingness.
Sea mammals evolved sharp hearing to take advantage of sound’s reach and
to compensate for poor visibility. The heads of whales and dolphins are
mazes of resonant chambers and acoustic lenses that give the animals
not only extraordinary hearing but complex voices they use to
communicate.
In recent decades, humans have added raucous clatter to the primal
chorus. Mr. Bahtiarian noted that the noise of a typical cargo vessel
could rival that of a jet. Even louder, he added, are air guns fired
near the surface from ships used in oil and gas exploration. Their waves
radiate downward and penetrate deep into the seabed, helping oil
companies locate hidden pockets of hydrocarbons.
Marine biologists have linked the human noises to reductions in
mammalian vocalization, which suggests declines in foraging and
breeding.
Worse, the Navy estimates that blasts from its sonars — used in training
and to hunt enemy submarines — result in permanent hearing losses for
hundreds of sea mammals every year and temporary losses for thousands.
All told, annually the injured animals number more than a quarter
million.
The federal sound study examined all these noises but zeroed in on
commercial shipping because it represented a continuous threat, in
contrast to sporadic booms. For North Atlantic shipping, the project
drew up more than two dozen maps. All their scales went from red (115
decibels at the top) to orange and yellow, and then to green and blue
(40 decibels at the bottom). The maps presented the results in terms of
annual averages rather than peaks.
A decibel is a measure of noise, and peak levels underwater can be
incredibly loud. When monitored by a hydrophone at a distance of one
meter (about three feet), a seismic gun produces 250 decibels, an oil
tanker 200 decibels and a tugboat 170 decibels, according to Mr.
Bahtiarian.
To draw up its annual maps, the sound project used computers to average
out such peaks over time, as well as to slowly diminish the noises as
they traveled over the ocean’s vast reaches. The study also chose to
model the low frequencies used by sea mammals for hearing and
vocalization, and tracked how far the sounds penetrated.
Maps of the North Atlantic show mostly oranges in the upper waters, but
many blues appear as the readings go downward as deep as one kilometer,
or six-tenths of a mile. At that depth, the sound maps clearly show the
ability of the Mid-Atlantic Ridge — a mountain chain that runs down the
ocean’s middle — to diminish the radiating noises by breaking up
patterns of sound waves.
Dr. Hatch, of the sound study, said too many areas of the ocean surface
(where sea mammals and whales spend most of their time) are orange in
coloration, denoting high average levels.
“It’s like downtown Manhattan during the day, only not taking into
account the ambulances and the sirens,” she said. “I’d be happier saying
it was like a national park.”
Vessels for fishing and research, including new ships being built for
N.O.A.A., are already being quieted around the world. The trend derives
not so much out of concern for sea mammals but from the realization by
oceanographers that quiet ships let them do better science.
Marine engineers say the mechanics of ship quieting are relatively
straightforward if applied in the design stage. The biggest factor is
the ship’s propeller, which has to be shaped exactly right to lessen
cavitation.
The noise arises when the force of a propeller cutting through seawater
results in millions of voids and bubbles, which then collapse violently.
Experts say quiet propellers have a benefit beyond helping sea mammals
in that some kinds can reduce fuel consumption.
Other measures for quieting include adding layers of sound-absorbing
tiles to the walls of noisy rooms as well as mounting engines, pumps,
air compressors, and other types of reciprocating machinery on vibration
isolators. Mr. Bahtiarian of Noise Control Engineering, who has written
extensively on the topic in professional journals and for expert
committees, noted that a parallel to ship quieting had been under way in
the airline industry for decades. City officials and airport neighbors,
as well as federal officials, have prodded the manufacturers of jet
engines to find ways of reducing noise.
Experts note that the magnitude of the problem on land and sea is
similar, in that the global fleets of commercial jets and ships both
number in the tens of thousands. But designing better ships to quiet the
ocean, Mr. Bahtiarian said, will take longer.
“A ship’s lifetime is 30 or even 50 years,” he noted, “so it could be a
lot longer” before improved designs start transforming the fleet.
Still, Mr. Bahtiarian added, the quieting trend seems inevitable given
the new reports about sound pollution and rising awareness about the
dangers to whales, dolphins and other sea mammals.
“The technology is there,” he said. “It seems like it’s just a matter of time.”
No comments:
Post a Comment