Oceans to get noisier with climate change

As the ocean chemistry changes with global warming, underwater noise is likely to become less muted.

Climate change sounds bad to a lot of people. It might sound even worse to underwater animals.

As ocean chemistry changes with global warming, a new study found, underwater noises could travel more than 70 percent further in the next century. The effect will be most extreme at high latitudes and in deep channels.

No one knows how the combination of more noise and farther-reaching noise will affect animals that live — and listen — under the sea.

“The ocean is becoming more transparent to sound,” said Tatiana Ilyina, an oceanographer at the University of Hawaii in Manoa. “In other words, it’s becoming louder.”

As levels of carbon dioxide rise in the atmosphere, ocean waters are becoming more acidic. Besides decreased calcification in corals and other problems, ocean acidification causes changes in concentrations of salts in seawater. Some of those molecules, including boron ions, normally absorb sounds, particularly low-frequency sounds.

With acidification, numbers of boron ions drop, and low-frequency sounds travel farther.

Scientists have already noted a change in both ocean pH and in the way sound travels underwater. Ilyina and colleagues used climate models to predict what the future holds.

If we carry on with current levels of greenhouse gas emissions, they reported in the journal Nature Geoscience, pH would drop by 0.6 units, leading to a 60 percent decrease in sound absorption. In the worst-case scenario, sound absorption would drop by more than 70 percent by the year 2100.

Emily Sohn, Discovery News, 21 December 2009. Article.

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