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New Scientist Magazine: Oil spills go a long way under ice

EXTRACT: “…the endangered western Pacific grey whale would be hard hit by any leaks at the Sakhalin drilling site off Russia’s east coast, because its oil platforms sit near the whales’ only known summer feeding ground.”

14 December 2007
Jason Palmer
Magazine issue 2634

If an oil well or pipeline should ever spring a leak in the Arctic, let’s hope it doesn’t happen under the ice: a 3D map of the contours under an ice sheet has revealed that such a spill would spread more than 10 times further than previously thought, due to the complex nature of the ice.

Until now, computer models and small-scale laboratory tests could offer only simplistic predictions about how bad an oil spill from a broken pipeline or the “blowout” of a well under an ice sheet would be. This is because information about the ice sheet’s subsurface structure tends to be based on sporadic data from boreholes.

Jeremy Wilkinson from the Scottish Association for Marine Science in Oban and his colleagues wanted to create a more detailed model and so sent an autonomous underwater vehicle beneath the ice off the coast of Greenland in 2004. The team used the craft to make a 3D picture of the underside of the ice.

Perhaps not surprisingly, they found borehole data to be woefully inadequate: not only were there more subsurface nooks and crannies than predicted, but they were heavily interconnected and the ice itself varied considerably in thickness.

When they fed all of this new information into a computer model, they saw that after a spill, the buoyancy of the oil would drive it up through the interconnected channels as it found its way to the thinner ice, where it would eventually pool over a much wider scale than that predicted by previous models. As “Beluga whales could come up for air at the holes and cracks in the ice where spilt oil would concentrate” such, a spill of 5000 cubic metres of oil – typical for a pipeline break -would spread over more than 2 square kilometres on average, an area nearly 13 times what previous predictions suggested (Geophysical Research Letters, DOI: 10.1029/2007GL031754).

Curiously, earlier models had failed to take into account that oil in water is buoyancy-driven and will flow to thinner parts of the ice, says Wilkinson. “When you think about it, that’s how oil should flow and how flow is treated in any other situation -like flooding,” he says.

Environmental groups have long argued that response plans to an Arctic spill are inadequate -and they are working on previous low estimates of oil spread beneath the ice. Although an icy spill cannot spread as widely as one in open water, it can hang around for much longer. The ice-water border grips more oil than the air-water border, and ice also allows oil to pool.

Identifying where oil is trapped beneath the ice is difficult if the exact location of the pipe rupture is unknown, because conventional techniques for remote sensing oil are inadequate. For example, ground-penetrating radar is absorbed by the ice. What’s more, solutions for cleaning up the oil are unsophisticated. The best techniques on offer involve attempting to suck the oil out through holes in the ice, or burning it off.

Peter Ewins, director of species conservation for WWF, points out that an Arctic spill could have a serious impact on marine species, and especially whales. Beluga whales travel far beneath ice-covered waters off Alaska, coming up for air at the holes and cracks in the ice where spilt oil would concentrate. And the endangered western Pacific grey whale would be hard hit by any leaks at the Sakhalin drilling site off Russia’s east coast, because its oil platforms sit near the whales’ only known summer feeding ground.

http://environment.newscientist.com/article/mg19626344.000-oil-spills-go-a-long-way-under-ice.html

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