Scientist sets base line for ocean noise
Rain falling on the surface of the ocean can be heard more than a mile deep, and at some frequencies it is louder than passing ships, according to oceanographer Jeff Nystuen.
Nystuen, of the Applied Physics Laboratory at the University of Washington, is studying how sound travels through the ocean to better understand how manufactured noises might affect marine creatures.
"We don't really know what is too loud underwater, and we need to know what the base line is," Nystuen said.
Loud underwater noises, particularly U.S. Navy sonar, have long been blamed by environmentalists for the fatal beachings of whales.
The Natural Resources Defense Council and other plaintiffs alleged in a federal lawsuit last fall that the Navy's midfrequency sonar used to detect enemy submarines disturbs and sometimes kills whales and dolphins.
The Navy settled a similar lawsuit three years ago by agreeing to limit its peacetime use of experimental low-frequency sonar.
To find out what sounds sea creatures are exposed to, Nystuen moored microphones at spots around the world to collect a year's worth of sound. He spoke Thursday at the biannual ocean sciences meeting of the American Geophysical Union in Honolulu.
Building up his inventory of sounds since 1999, Nystuen is looking for long-term patterns.
His findings show that among higher-pitched sounds, rain is the loudest, far louder than passing ships. Among lower-pitched sounds, shipping is the loudest, followed by rain.
Nystuen's recordings have not been able to account for creatures' behavior in response to noise.
"If you came to see me in Seattle and said, 'I want to see some killer whales,' I would take you to Haro Strait, which is the noisiest environment that I've ever made measurements in," he said. Haro Strait lies between the United States and Canada near Victoria.
Nystuen said his listening devices could be used to make sure animals are not nearby before testing sonar.
The U.S. Army Corps of Engineers spent three years figuring out how best not to harm protected species during a project completed this summer at the port of Miami that required blasting rock out of the harbor, said Terri Jordan, a biologist with the corps.
Before triggering any explosion, a 4,000-foot perimeter was searched by helicopter and boat for animals including porpoises, manatees and sea turtles. If any animal wandered within about 2,500 feet of the blast site, the project stopped until it left. The width of the perimeter was calculated by doubling the distance usually used to protect Navy divers from bomb blasts.
Five minutes before the main explosion, a smaller "fish scare" blast was set off to scatter any fish in the area.