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Tiny Organisms Affected By Ocean Acidification, Global Warming

March 9, 2009

A new study found that ocean acidification caused by climate change is stripping away the protective shell of tiny yet vital organisms that absorb huge amounts of carbon pollution from the atmosphere, the AFP reported.

The study found that the calcium carapace of microscopic animals called foraminifera living in the Southern Ocean have fallen in weight by a third since the start of the Industrial Revolution.

The tiny organisms inhabit the surface waters of oceans around the world and are an important part of the ecological chain and also provide a bulwark against global warming.

The nearly microscopic creatures create calcium-based shells out of carbon dioxide (CO2) from the air. Their carbon-rich shells sink to the ocean floor when they die, effectively storing the atmospheric CO2 forever.

Studies in the past have suggested that other marine animals like corals are losing their ability to form exoskeletons from calcium. Potential causes range from rising temperatures and nutrient runoff from coastal agriculture to acidification.

The authors said it was the first study focus exclusively on acidification and tie it to greenhouse-gas pollution, which is driven especially by the invisible product of burning oil, gas and coal.

Co-author William Howard of the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart, Tasmania, said it is the invasion of anthropogenic (man-made) CO2 that is causing this particular source of acidification.

As the shells drifted toward the sea floor, researchers collected shells of one foraminifera species, Globigerina bulloides, and compared them to older specimens that had sunk several hundred years earlier.

The authors wrote in the online edition of the journal Nature Geoscience that the newer shells had 30-to-35 percent less mass.

Howard said if forams and other shell makers are not making shells, it could change the transfer of carbon from the surface ocean into the deep ocean.

“That changes the efficiency of the biological pump, and would tend to lessen the degree to which the ocean takes up carbon,” he said in an interview with the AFP. “That’s a feedback that we have to be concerned about.”

Scientists have only become aware of the extent of ocean acidification in the last five years and its potential to disrupt Earth’s carbon cycle, which balances the absorption and release of CO2 into the atmosphere.

Howard said the problem with this impact is that it is so persistent and so long-lived, unlike other pollution carbons.

“We will have a harder time turning this impact around,” he said, adding that the geo-chemical mechanisms that buffer acidification work very slowly.

“It is like taking an antacid tablet for an upset stomach and then having to wait hundreds — or thousands — of years for it to work.”

Experts fear that if the loss of shell mass threatens the survival of the amoeba-like creatures, it could also disrupt a food chain reaching from the plankton they eat, all the way up to large sea mammal such as whales.

“We don’t know yet what those impacts might be,” Howard said.

Image Caption: Globigerina bulloides magnified 330 times. (Photo: L. Northcote)

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