This was observed by a team of scientists, led by Geraint Tarling, from the British Antarctic Survey in Cambridge, UK. They captured free-swimming snails called pteropods, from the Southern Ocean in early 2008. After studying them under an electron microscope, the team discovered that the outer layers of the shells showed signs of corrosion.
Greenhouse gases in the atmosphere, and particularly carbon dioxide, not only warm the planet but also affect the chemistry of the oceans. When dissolved in the water, CO2 forms carbonic acid which causes the pH to drop. This process creates more available hydrogen atoms in the water, which react with carbonate ions and make them unavailable to react with calcium.
This process is now observed to happen faster than any time throughout the past 300 million years.
Considering that shells, corals and molluscs build their shells by taking up calcium carbonate from the water, it is now clear that these organisms will suffer the most.
The form of calcium carbonate that these animals need is called aragonite. This is a very sensitive form, which is predicted to be a deficit by 2050. Although it is relatively abundant now, some regions are already experiencing depletion in concentration. In addition, as Tarling points out, the change will become most visible firstly in the polar oceans, and shortly after in the tropics.
Tarling visited the Southern Ocean near South Georgia. This region is known to be naturally low in aragonite, however when ocean acidification is accelerated, the mineral at the surface is dangerously scarce.
Toby Tyrrell from the National Oceanography Centre in Southampton predicts that the Arctic is likely to become undersaturated. This has already been observed in some parts of the Antarctic, for example near the north coast of Canada.
The only way to prevent this from happening is to reduce carbon emissions. Although some suggest that extra lime could be added to the oceans, scientists are certain that the costs and the amounts needed to balance the concentrations are huge.