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.
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