Sounds travel farther underwater as worlds oceans become more acidic

September 30th, 2008 - 2:43 pm ICT by ANI  

Washington, September 30 (ANI): A new research has suggested that as seawater becomes more acidic because of carbon dioxide from the atmosphere dissolving in the oceans, an unexpected side effect is taking place in the form of sounds traveling farther underwater.

The research has been conducted by marine chemists at the Monterey Bay Aquarium Research Institute in California, US.

Conservative projections by the Intergovernmental Panel on Climate Change (IPCC) suggest that the chemistry of seawater could change by 0.3 pH units by 2050.

Keith Hester and his coauthors calculate that this change in ocean acidity would allow sounds to travel up to 70 percent farther underwater.

This will increase the amount of background noise in the oceans and could affect the behavior of marine mammals.

Ocean chemists have known for decades that the absorption of sound in seawater changes with the chemistry of the water itself.

As sound moves through seawater, it causes groups of atoms to vibrate, absorbing sounds at specific frequencies. This involves a variety of chemical interactions that are not completely understood.

However, the overall effect is strongly controlled by the acidity of the seawater. The bottom line is the more acidic the seawater, the less low- and mid-frequency sound it absorbs.

Thus, as the oceans become more acidic, sounds will travel farther underwater.

According to Hesters calculations, such a change in chemistry will have the greatest effect on sounds below about 3,000 cycles per second.

This range of sounds includes most of the low frequency sounds used by marine mammals in finding food and mates. It also includes many of the underwater sounds generated by industrial and military activity, as well as by boats and ships.

Such human-generated underwater noise has increased dramatically over the last 50 years, as human activities in the ocean have increased.

The MBARI researchers say that sound already may be traveling 10 percent farther in the oceans than it did a few hundred years ago.

However, they predict that by 2050, under conservative projections of ocean acidification, sounds could travel as much as 70 percent farther in some ocean areas (particularly in the Atlantic Ocean).

This could dramatically improve the ability of marine mammals to communicate over long distances. It could also increase the amount of background noise that they have to live with. (ANI)

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