Ocean Racket

Science World, Oct 4, 1999 by Miguel Vilar

If you ever thought of an ocean swim as a quiet escape, think again. Today, oceans are noisier than a motorcycle without a muffler. Boat propellers, deep-sea drills, and sonar--sound waves that ships bounce off ocean floors to map them--often blast sounds as loud as 170 decibels. That's 10,000 times louder than the most deafening rock concert. And that's set off alarm bells for scientists concerned about undersea life. They worry that exploding ocean noise may confuse and even kill animals that use sound to find food and mates.

"Marine mammals like dolphins and whales use sound like humans use sight," says Roger Gentry, oceanographer (ocean scientist) for the National Marine Fisheries Service in Silver Spring, Maryland. "If they can't hear, they could die." Whales, for example, communicate within their own group or pod through sounds as high as 20,000 hertz--the same frequency as most of today's ocean racket.

Also, sound travels four times faster in water than in air: 1,230 meters per second versus 340 meters per second-- because water molecules are packed tighter than air molecules. So underwater sound travels longer distances before it diminishes. A dolphin swimming along the California coast may be able to hear deep-sea drilling 7,000 miles (11,300 kilometers) away off the China coast! Researchers have no concrete data on how ocean noise pollution will impact sea life. But they do know such noise is definitely not music to fish ears!