This Ocean's Too Noisy

Aug. 23, 2006 — -- For many animals in the ocean, sound is everything. Some depend on it to find food, some need it to communicate with others, some need it to navigate. But the ocean, once known as the silent deep, has become a much noisier place.

Scientists at the Scripps Institution of Oceanography in San Diego say the noise level in what should be a fairly quiet zone more than 180 miles offshore has risen significantly over the last few decades, apparently because ships are bigger, faster and more powerful than they were before.

"The levels are high enough that it's of concern," says John Hildebrand, professor of oceanography at Scripps, which is part of the University of California, San Diego.

Since 1964, the noise level has risen 10 to 12 decibels, according to a report by Hildebrand and colleagues in the August issue of the Journal of the Acoustical Society of America. A decibel is a unit of measurement of sound intensity, and while 10 to 12 might not seem like a lot, it could be quite significant in the ocean.

"In background noise it's roughly the difference between sitting in a library and being in a Wal-Mart," says oceanographer and co-author of the report, Mark McDonald of Whale Acoustics, a small research firm in Bellvue, Colo.

The scientists don't know exactly how much of a problem the increase in noise poses for marine animals. Since the change has taken place over decades, it's hard to isolate a single cause and effect. But what is clear is the fact that the ocean has become much noisier, and that can't be good for many critters.

Whales that use sound to communicate "won't be able to hear each other as far away," says McDonald. "But is that a problem?"

Whales, he says, have shown an ability to adjust to changing conditions.

For some time now, Hildebrand, McDonald and Sean Wiggins, also of Scripps, have been monitoring the noise level with a sophisticated instrument on the bottom of the ocean near San Nicolas Island, off the coast of San Diego. They have been able to document the change partly because of a bit of good luck.