Arctic seas turn to acid, putting vital food chain at risk

Carbon-dioxide emissions are turning the waters of the Arctic Ocean into acid at an unprecedented rate, scientists have discovered. Research carried out in the archipelago of Svalbard has shown in many regions around the north pole seawater is likely to reach corrosive levels within 10 years. The water will then start to dissolve the shells of mussels and other shellfish and cause major disruption to the food chain. By the end of the century, the entire Arctic Ocean will be corrosively acidic.

"This is extremely worrying," Professor Jean-Pierre Gattuso, of France's Centre National de la Recherche Scientifique, told an international oceanography conference last week. "We knew that the seas were getting more acidic and this would disrupt the ability of shellfish – like mussels – to grow their shells. But now we realise the situation is much worse. The water will become so acidic it will actually dissolve the shells of living shellfish."

Just as an acid descaler breaks apart limescale inside a kettle, so the shells that protect molluscs and other creatures will be dissolved. "This will affect the whole food chain, including the North Atlantic salmon, which feeds on molluscs," said Gattuso, speaking at a European commission conference, Oceans of Tomorrow, in Barcelona last week. The oceanographer told delegates that the problem of ocean acidification was worse in high latitudes, in the Arctic and around Antarctica, than it was nearer the equator.

"More carbon dioxide can dissolve in cold water than warm," he said. "Hence the problem of acidification is worse in the Arctic than in the tropics, though we have only recently got round to studying the problem in detail."

About a quarter of the carbon dioxide pumped into the atmosphere by factories, power stations and cars now ends up being absorbed by the oceans. That represents more than six million tonnes of carbon a day.

This carbon dioxide dissolves and is turned into carbonic acid, causing the oceans to become more acidic. "We knew the Arctic would be particularly badly affected when we started our studies but I did not anticipate the extent of the problem," said Gattuso.

His research suggests that 10% of the Arctic Ocean will be corrosively acidic by 2018; 50% by 2050; and 100% ocean by 2100. "Over the whole planet, there will be a threefold increase in the average acidity of the oceans, which is unprecedented during the past 20 million years. That level of acidification will cause immense damage to the ecosystem and the food chain, particularly in the Arctic," he added.

The tiny mollusc Limacina helicina, which is found in Arctic waters, will be particularly vulnerable, he said. The little shellfish is eaten by baleen whales, salmon, herring and various seabirds. Its disappearance would therefore have a major impact on the entire marine food chain. The deep-water coral Lophelia pertusa would also be extremely vulnerable to rising acidity. Reefs in high latitudes are constructed by only one or two types of coral – unlike tropical coral reefs which are built by a large variety of species. The loss of Lophelia pertusa would therefore devastate reefs off Norway and the coast of Scotland, removing underwater shelters that are exploited by dozens of species of fish and other creatures.

"Scientists have proposed all sorts of geo-engineering solutions to global warming," said Gattuso. "For instance, they have proposed spraying the upper atmosphere with aerosol particles that would reduce sunlight reaching the Earth, mitigating the warming caused by rising levels of carbon dioxide.

"But these ideas miss the point. They will still allow carbon dioxide emissions to continue to increase – and thus the oceans to become more and more acidic. There is only one way to stop the devastation the oceans are now facing and that is to limit carbon-dioxide emissions as a matter of urgency."