According to the National Academy of Sciences, the risk of a serious oil spill in the arctic is growing due to the uptick in ocean shipping traffic and oil and gas activities.

Complicating matters, scientists say, is the fact that increasing amounts of ice floating in the region could obscure evidence of any sort of oil spill, thus delaying a response effort.

That's why scientist are working on techniques to spot invisible oil spills in the arctic. So far, one solution stands out: sonar. Aiming high-frequency sonar chirps at sheets of ice has been shown to reveal oil hidden beneath ice. By analyzing the sonar echoes that bounce back, scientists can even use the technique to spy oil slicks sandwiched between layers of ice.

"We were able to distinguish two different signatures: oil together with ice versus just ice alone," Christopher Bassett, a researcher at Woods Hole Oceanographic Institution, told Scientific American.

At the annual Acoustical Society of America's meeting in Providence, Rhode Island, today, Basset and his fellow researchers presented their research into oil-spotting sonar.