Saturday, January 16, 2010

More CO2 means noisier deep oceans: UH researchers

Among the weird effects of our continued dumping of carbon-dioxide into the environment is that oceans are getting noisier.

(Image: Waves are among the sources of low-frequency ocean noise. Credit: SOEST.)

Here's how that works:

Researchers are finding that as carbon-dioxide is absorbed into the ocean, the ocean is getting more acidic. A more acidic ocean absorbs less sound at certain wavelengths—essentially low-frequency sound. That may mean noise is louder, farther.

Oceanographers Tatiana Ilyina and Richard Zeebe of the University of Hawai'i's School of Ocean and Earth Science and Technology, and Peter Brewer of the Monterey Bay Aquarium Research Institute, described the phenomenon in a recent issue of the journal Nature Geoscience.

“If we continue to emit carbon dioxide at business-as-usual rates, the pH of surface seawater will drop by 0.6 units by the year 2100. As a result, the absorption of 200 Hz sound would decrease by up to 70%”, Ilyina said.

This range of sound frequency is used by some marine animals, and is produced by weather effects like rain and wave action, as well as by human action like shipping, ocean construction and some sonar systems

What all this might mean to marine creatures, or to the military's use of sonar, is not entirely clear, the authors said.

“We don’t fully understand what the impacts of these changes in ocean acoustics will be. Because of decreasing sound absorption, underwater sound could travel farther, and this could lead to growing noise levels in the oceans. Increasing transparency of the oceans to low-frequency sounds could also enable marine mammals to communicate over longer distances,” Ilyina said.

The paper:

Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions. Ilyina, T., R. E. Zeebe, and P. G. Brewer. Nature Geoscience. Advance Online Publication, Dec 20, 2009, DOI: 10.1038/ngeo719

© Jan TenBruggencate 2010

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