This Ocean Invaded Its Neighbor Earlier Than Anyone Thought

The saltier Atlantic broke through layers of ice and freshwater, contributing to the Arctic’s warming.

Arctic. Atlantic. Long ago, the two oceans existed in harmony, with warm and salty Atlantic waters gently flowing into the Arctic. The layered nature of the Arctic — sea ice on top, cool freshwater in the middle and warm, salty water at the bottom — helped hold the boundary between the polar ocean and the warmer Atlantic.

But everything changed when the larger ocean began flowing faster than the polar ocean could accommodate, weakening the distinction between the layers and transforming Arctic waters into something closer to the Atlantic. This process, called Atlantification, is part of the reason the Arctic is warming faster than any other ocean.

“It’s not a new invasion of the Arctic,” said Yueng-Djern Lenn, a physical oceanographer at Bangor University in Wales. “What’s new is that the properties of the Arctic are changing.”