"Archived" heat trapped beneath the surface of the Arctic has the potential to melt all of the region's sea ice, the scientists warn.
The study published in the journal Science Advances shows that Arctic sea ice is not threatened only by the melting of ice on its edges.
Warmer water, hundreds of miles away, has penetrated deep into the Arctic, researchers have found.
They traced the source hundreds of kilometers to the south, where reduced sea ice exposed the surface ocean to more summer solar heat. Conversely, the Arctic winds drive the warmer waters to the north, but below the surface waters.
"Currently, this heat is trapped beneath the surface layer, and when mixed to the surface, there is enough heat to completely melt the sea ice that covers that region for most of the year," she said.