The complex structure of sea ice made the implications of an oil spill in ice a difficult affair, writes Nancy Bazilchuk in an article on geminiresearchnews.com.
She noted that ice was more complicated than people think. It was not solid, but more like a sponge, shot through with tiny channels and pores that can contain salt, briny sea water, or air bubbles.
Oil is lighter than seawater so, if it is spilled, it can migrate upward, into the tiny channels in the ice, which can trap it, complicating clean up.
However, Bazilchuk admitted that “the truth is that Arctic sea ice is so complex that it is difficult to know exactly how oil and ice will interact”.
Sönke Maus, a postdoc at the Norwegian University of Science and Technology, and a member of research group MOSIDEO (Microscale interaction of oil with sea ice for detection and environmental risk management in sustainable operations) said that studying it was difficult because traditional sampling and tests might crush or distort the very structure you were trying to understand. “We are looking at channels that are one-tenth of a millimeter in diameter, and if we want to know what is happening in the ice, we need a three dimensional image”, Maus said.
If crude oil is spilled in the ocean, it normally floats. But if the oil is released or spilled under a lid of sea ice, it will be trapped under the ice.
“Depending on the microstructure of the sea ice, the oil may be trapped or it may keep moving up towards the surface. So if we want to evaluate the environmental consequences of an under-ice oil spill, we really want to know when and if the oil will come to the surface, how far the ice will drift before the oil surfaces, and how much of the oil will be trapped in the ice when the ice finally melts”, Maus said.
The channels and pores in the sea ice are different, depending upon where they are located in the ice. At its surface, where the ice is in contact with cold air temperatures, sea ice has smaller and less connected pores.
Maus said that oil would normally only enter larger pores; it also needs to push the seawater out of the pores. During wintertime the ice is often too cold at the surface to allow for this, meaning that the oil will be trapped. Then, during spring, the oil could migrate to the surface.
Once the oil surfaces, Maus said rthere was a window of only about one week. “The only realistic approach to remove this oil from the surface of a closed ice cover is to burn it.” But after a week, the oil is said to be “weathered” and can no longer be removed by burning. “This oil then threatens the arctic ecosystem,” Maus said.