Sounding an alarm over deep sea noise

The ocean depths have become a noisy place, thanks to the sonar blasts of military exercises, the booms from air guns used in oil 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 clamour is particularly dangerous to whales, which depend on their acute hearing to locate food and one another. To fight the din, the US 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.

It is no small ambition: The sea covers more than 70 per cent of the planet's surface. The federal effort seeks to document human-made noises in the ocean and transform the results into the world's first large sound maps. The visualisations use bright colours to symbolise the sounds radiating out through the oceanic depths, frequently over distances of hundreds of miles.

The US National Oceanic and Atmospheric Administration began the effort in 2010 at the behest of Jane Lubchenco, a prominent marine biologist. Hatch and her colleagues assembled a team of sound experts, including HLS Research, a consulting firm in La Jolla, California. 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 Defence Council, a private group in New York that has sued the US Navy to reduce sounds that can harm marine mammals, praised the maps as "magnificent" and their depictions of sound pollution as "incredibly disturbing."

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. Scientists note that the noise of a typical cargo vessel could rival that of a jet. Even louder, they say, 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 human noises to reductions in mammalian vocalisation, which suggests declines in foraging and breeding. Worse, the US Navy estimates that blasts from its sonars result in permanent hearing losses for hundreds of sea mammals every year and temporary losses for thousands.

The federal sound study examined all these noises but zeroed in on commercial shipping because it represented a continuous threat. Vessels for fishing and research, including new ships being built for NOAA, are already being quieted around the world. 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.

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