Weather Eye: noisy oceans threaten life under water

The world’s oceans are growing noisier, thanks to the rising levels of carbon dioxide. This could create a cacophony of sounds that will make life difficult for whales and dolphins, which use their shrills and rumbles for navigation and communication and, rather like a room full of people shouting at each other, their calls could get lost in an underwater din.

It seems unbelievable that carbon dioxide would make a difference to anything on Earth because it only makes up about 0.04 per cent of the atmosphere. But when air dissolves in water, the carbon dioxide makes carbonic acid. Although a very weak acid, it slowly eats away chalk and limestone, which is how Cheddar Gorge and its caves were made.

As carbon dioxide dissolves in the oceans it is turning the water more acidic. This has an impact on sound travelling through the water, because sound waves are absorbed by certain types of charged molecules that stick together in seawater. As the sea becomes acidic, the charged molecules absorb less sound, and so the sound waves travel further.

A recent study has found that carbon dioxide absorbed by the oceans has increased sound travel by about 10 per cent throughout the Atlantic and Pacific. And by mid-century this is expected to rise up to 70 per cent further. With noise travelling further, this could create an underwater din that will make life much more difficult for whales and fish that live on reefs that also use sound.

The increasingly acid oceans are also hurting sea creatures such as diatoms and corals. Their shells are made of carbonate that is corroded by carbonic acid.

Paul Simons, Times Online, 6 October 2008. Article.

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