Ocean commotion

A rise in global shipping is turning up the volume in the ocean. In the 1960s the U.S. Navy recorded ambient noise at several sites in the waters off the west coast of North America. Recently Mark A. McDonald, an acoustician at WhaleAcoustics in Bellvue, Colorado, and two colleagues revisited one of those sites, off southern California, and continuously recorded the sounds of the deep from November 2003 until March 2004.

Compared to the sounds the Navy recorded forty years earlier, the team discovered, low-frequency noise from ships has increased by at least ten decibels. That's ten times the former noise level, equivalent to the difference between the ambient noise in a library and that in a busy, big-box retail store, says McDonald. And the entire northeast Pacific Ocean is probably just as loud: the test-recording site is well away from shipping lanes, but sounds that originate throughout the region can be heard there.

Commercial ships doubled in number, quadrupled their cargo tonnage, and dramatically increased their speed and horsepower between 1965 and 2003. The mounting racket has unknown consequences for marine mammals, particularly whales and dolphins, which communicate with sound over long distances. But the animals will just have to get used to the din, says McDonald, because the volume is likely to continue rising. One possible note of optimism rises above the noise: dampening the engines and propellers of the largest 1 percent of the world's vessels would quiet the ocean down considerably. (Journal of the Acoustical Society of America 120:711-8, 2006)

COPYRIGHT 2006 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning