Scuffs, scrapes, and gouges found atop undersea plateaus and ridges in the Arctic Ocean suggest that kilometer-thick ice shelves covered much of the ocean there during some previous ice ages. The unexpected features show up in sonar images collected by a U.S. nuclear submarine in 1999.
Parallel grooves mark the submerged Chukchi Plateau, north of Alaska, at depths as great as 700 meters. These features, spaced between 50 and 200 m apart, extend in some cases for more than 15 kilometers, says Leonid Polyak, a paleo-oceanographer at Ohio State University in Columbus. He and his colleagues describe their findings in the March 22 Nature.