Richard A. Lovett, National Geographic News 2 Oct 08;
As the world's oceans become more acidic, the underwater sounds that whales and other marine mammals depend on for survival may turn into a confusing racket, a new study says.
That's because the ocean's ability to conduct sound is expected to increase dramatically due to global warming.
The shift could make it easier for rare whales to find each other and reproduce, researchers say.
More likely, though, the effect would be comparable to a person in a crowded place straining to talk over all the chatter.
"What that means is that the background level of noise in the ocean—say wave noise or ship noise—will increase," said study co-author Peter Brewer, a geochemist at the Monterey Bay Aquarium Research Institute in California.
(Related: "Noisy Eaters Are Cause of Mysterious Ocean Sounds" [August 18, 2008].)
John Hocevar, oceans campaign director for Greenpeace USA, agreed.
"This is a real disaster for marine life," he said.
Soda Water Acid
Sound transmission in oceans is affected by the concentration of various ions, or charged atoms, said Keith Hester, a member of the research team.
The ions are affected by the water's pH, which becomes more acidic as carbon dioxide from fossil fuel burning is absorbed.
The result is carbonic acid, the same acid found in soda water.
Ocean acidity, Hester said, is projected to increase by .3 pH points between now and 2050. That may not seem like much, but the change will spur a 70 percent increase in the distance sound will travel.
"We were surprised to see how big it was," Hester said.
Less certain are the ramifications.
Previous studies have suggested that high-powered sonar may cause hearing loss and other injuries to marine mammals.
Recent findings have revealed that reef fishes use sound to locate their reefs.
In addition to animal impacts, military sonar operators may have more trouble distinguishing faint signals from background noise.
The new study appeared this week in in the journal Geophysical Research Letters.
"Impossible to Predict"
Marine biologists are cautious about predicting about what may happen to marine animals in seas that conduct sound better.
"The effects on biology are uncertain at the moment," Richard Zeebe of the University of Hawaii said in an email.
But it's clear that the change in sound transmission is an unanticipated side effect of fossil fuel burning, experts say.
"This is a good example that we're making very big changes to our oceans," said co-author Hester.
"There's a hundred million tons of carbon dioxide absorbed per hour by the oceans. This is really changing a lot [of things] that we're still trying to understand."
