BP's slowdown of an Alaskan oilfield because of pipeline corrosion highlights the environmental risks of oil drilling in the Arctic where animals and plants are vulnerable and spills can be costly to clean up, experts say.
The British oil group BP has shut in half the output at its giant Prudhoe Bay field after finding pipeline corrosion and a tiny leak, estimated by BP at less than a tonne of oil.
The cutback has prevented damage to the Arctic, where many animals and plants live on the edge of their ranges because of the cold and winter dark. Many Arctic nations are looking north for oil and gas, bringing new risks.
"Problems for oil companies in the Arctic are the low temperatures, slow degradation of oil and difficulties in getting rid of it," said Lars-Otto Reiersen, head of the Arctic Monitoring and Assessment Programme (AMAP) run by the eight nations with Arctic territories.
The Alaskan environment around Prince William Sound has yet to recover fully after the Exxon Valdez tanker spilt 37,000 tonnes of crude in 1989. The Russian Arctic has been scarred by spills including 150,000 tonnes from a pipe near Usinsk in 1994. "Corrosion has been the main problem in Russian pipelines," Reiersen told Reuters. The Oslo-based AMAP groups the United States, Russia, Canada and five Nordic countries.
In the Arctic, oil evaporates more slowly than in warmer climates because of the cold and the lack of sunlight in winter. Bacteria and fungi that feed on oil function for less of the year, with the result that spills linger longer.
Seabirds such as guillemots and puffins are especially vulnerable because oil can stick their feathers together and let chill water through to their skin. "Even a small oil slick among birds in the Arctic can cause many deaths," Reiersen said.
Polar bears and some seals with fur face similar problems of lost insulation. Whales, with thick layers of blubber, are better protected from oil. Spills on land are less damaging and costly but vegetation can take years to recover.
Experts say oil companies lack full techniques for cleaning up oil spilt onto ice at sea. Oil trapped in ice in winter can drift off and thaw out in spring hundreds of kilometres (miles) away, complicating a clean-up and adding huge costs.
The Arctic is likely to become more accessible this century because of improved drilling technology and a retreat of polar ice apparently linked to global warming. The region could contain a quarter of the world's undiscovered reserves, according to some US official estimates.
"There will be increased activity and increased accessibility ... it's reasonable to assume that this will mean higher risks of spills," said Paal Prestrud, head of the Center for International Climate and Environmental Research in Oslo.
More transport as the ice melts - perhaps even a short-cut route across the Arctic Ocean - also increases the risks of shipping accidents or collisions with icebergs.