Marine animals dissolving in Southern Ocean acid
Researchers have revealed that the shells of sea snails are dissolving in a small patch of the Southern Ocean, providing the first evidence that marine life is already suffering as a result of man-made ocean acidification.
"This is actually happening now," New Scientist quoted Geraint Tarling of the British Antarctic Survey in Cambridge, UK, as saying.
The alarming situation came into light when Tarling and colleagues captured free-swimming sea snails called pteropods from the Southern Ocean in early 2008 and found under an electron microscope that the outer layers of their hard shells bore signs of unusual corrosion.
In addition to warming the planet, the carbon dioxide humans emit is changing the chemistry of the ocean. CO2 dissolves in water to form carbonic acid, making the water less alkaline.
According to scientists, the pH is currently dropping at about 0.1 per century, faster than any time in the last 300 million years.
Experiments in the labs have found that organisms with hard shells, such as corals and molluscs, will suffer as a result. To build their shells, corals and molluscs need to take up calcium carbonate from the water, but more carbonic acid means more hydrogen ions in the water. These react with carbonate ions, making them unavailable to form calcium carbonate.
The most vulnerable animals are those, like pteropods, that build their shells entirely from aragonite, a form of calcium carbonate that is very sensitive to extra acidity.
Aragonite-depleted regions are still rare, but they will become widespread by 2050, said Tarling.
The polar oceans will change fastest, with the tropics following a few decades after.
"These pockets will start to get larger and larger until they meet," he stated.
The only way to stop ocean acidification is to reduce our CO2 emissions, noted Toby Tyrrell of the National Oceanography Centre in Southampton, UK.
Add megatonnes of lime to the ocean has been suggested to balance the extra acidity. But Tyrrell said this is "probably not practical" because the amounts involved - and thus the costs - are enormous.