Researchers found the previously unknown structure during a three-part mission aboard the U.S. Coast Guard's icebreaker "Healy" to map the ocean floor in the Chukchi and Beaufort seas.

A file photo of the Chukchi Sea, one of the areas of the Arctic affected by atlantification. (Hossein Fatemi/Middle East Images/AFP via Getty Images) Warm Atlantic waters are rapidly reshaping the ...