Oceans gradually turning into vast 'fizzy drink'

LONDON, UK (29 Mar 2006) -- The oceans are gradually turning into a vast "fizzy drink", a transformation that could be catastrophic for ocean life. Levels of carbonic acid - the reaction product of water and carbon dioxide that is found in soda water - are increasing at a rate one hundred times faster than the world has seen for millions of years.

The cause is the ever-increasing level of CO2 in the atmosphere. And as well as devastating marine ecosystems, the knock-on effects of increasing acidification include harm to major economic activities such as tourism and fishing.

These are the conclusions of the first review of the state-of-knowledge about the acidification of the oceans. The report was produced by an international group of scientists, commissioned by the Royal Society, the UK's national academy of science.

The oceans are naturally alkaline but, since the industrial revolution, the sea surfaces have been turning ever more acidic. The report says that if CO2 emissions continue at current rates then by 2100 the pH of the sea will fall by as much as 0.5 units from its current level of pH 8.2. The pH scale runs from 1 (acidic) to 14 (alkaline), with 7 being neutral. And in the case of the oceans, the change would be effectively irreversible.

"It will take many thousands of years for natural processes to return the oceans to their pre-industrial state," says John Raven, at the University of Dundee, UK.

Chalk dumping

Raven and his colleagues looked at possible ways of neutralising the growing acidity, such as dumping chalk - a highly alkaline substance - into the sea, but all their ideas carried major problems of their own. "The only way to minimise the long-term consequences is to decrease CO2 emissions," Raven says.

The sea life expected to be worst hit include organisms that produce calcium carbonate shells, as these are harder to form in acidic waters. That means that corals, crustaceans, molluscs and certain plankton species will be at risk.



"It would not kill penguins, orca and other big animals directly, but it would affect the food chain with potentially damaging effects on larger animals," Raven explains.

Coral reefs face a three-pronged attack, the report says. There is global warming and coastal pollution, and now acidification. Raven says we can expect to see degradation of coral reefs in the tropics.

Giant blooms

And it does not stop there. There is an important group of photosynthetic plankton called coccolithophores that grow calcium carbonate shells and form giant "blooms" in spring and summer before sinking to the bottom of the ocean.

But the increasing acidification will hinder their ability to grow, meaning they remove less carbon from the atmosphere. This in turn will result in more carbonic acid being formed at the seas' surface.

"Calcium carbonate helps organisms to sink and enhances the biological pump," says Andrew Watson, an environmental biologist at the University of East Anglia, UK. The sea has absorbed about half of the CO2 produced by humans in the last 200 years and currently takes up one tonne of the gas each year for every person on the planet. But if the water becomes too acidic, the pump will not work and the ability of the oceans to mop up CO2 will fall, he says.

"Most climate scientists think the Kyoto targets themselves are wholly inadequate," Watson adds. "We need a sharp decline in CO2 emissions, down to half of today's levels."

SOURCE - New Scientist