Climate change fallout - it will become more noisy undersea

September 30th, 2008 - 5:03 pm ICT by IANS  

Washington, Sep 30 (IANS) Carbon dioxide is a gas that finds its way from the atmosphere into the ocean, turning seawater acidic. As the carbon dioxide concentration in the air increases due to human activities, seawater is turning more acidic. This not only impacts marine life directly, but also through unexpected indirect ways.Marine chemists at the Monterey Bay Aquarium Research Institute (MBARI) California, have found one unexpected side effect - sound will travel farther underwater.

Conservative projections by Intergovernmental Panel on Climate Change (IPCC) suggest that seawater chemistry could change by 0.3 pH units by 2050. Chemists measure acidity using pH units, with a scale that runs from 0 (the most acidic) to 14 (the least acidic, or most alkaline).

Keith Hester and co-authors from MBARI calculate that this change in ocean acidity would allow sounds to travel up to 70 percent farther underwater, which could affect the behaviour of marine mammals.

Ocean chemists have known for decades that the absorption of sound in seawater changes with the chemistry of the water itself. . . . The bottom line is the more acidic the seawater, the less low- and mid-frequency sound it absorbs.

According to Hester’s calculations, such a change will have the greatest effect on sounds below about 3,000 cycles per second (two and one half octaves above “middle C” on a piano).

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, according to an MBARI press release. The findings appeared in last Wednesday’s issue of Geophysical Research Letters.

MBARI researchers said that by 2050 . . . sounds could travel as much as 70 percent farther, 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.

Hester’s research shows once again how human activities are affecting the Earth in far-reaching and unexpected ways. As researchers put it, “the waters in the upper ocean are now undergoing an extraordinary transition in their fundamental chemical state at a rate not seen on Earth for millions of years”.

Cars, power plants and human activities have pumped hundreds of billions of tonnes of carbon dioxide into the air, half of which has been absorbed by the oceans.

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