Research found that sea limestone 'could help absorb carbon'

Adding limestone to the oceans could boost their ability to absorb carbon dioxide and help ailing coral reefs, it has been suggested.

The world's seas currently act as natural "carbon sinks", storing CO2 which dissolves into the water and bonds with carbonate ions.

But more and more CO2 pumped into the atmosphere - with scientists revealing earlier this week that levels had reached record highs and were growing at faster rates - means the seas are losing their ability to absorb the greenhouse gas.

This is because the chemical reaction with carbonate ions leaves fewer ions available to mop up the carbon dioxide.

It is also bad news for corals, which use carbonate ions and calcium to build their exoskeletons.

But Danny Harvey, a climate scientist at the University of Toronto, Canada, believes carbonate depletion can be tackled using limestone - which is made of calcium carbonate.

According to research reported in New Scientist magazine, the limestone is only slightly soluble in water, so it sinks and dissolves in lower parts of the ocean where carbonate levels are low. Years later the now carbonate-rich water returns to the surface through up-welling currents and can absorb more CO2.

His research, published in the Journal of Geophysical Research, suggests the best place to sprinkle the limestone is in the northern Pacific.

Ken Caldeira of the Carnegie Institution for Science in Stanford, California, told New Scientist the benefits of the process would come too late in the fight against global warming.

"It's unlikely to be of much help in preventing climate damage over the next decades at least," he warned.