Bowhead whales have navigated the Northwest Passage between the Atlantic and Pacific oceans for what could be the first time in nearly 10,000 years.
Researchers from the Greenland Institute of Natural Resources used satellite tracking to monitor the movements of the whales - and found that, last year, whales from both oceans entered the passage to reach an area called Viscount Melville Sound.
Bones found on beaches in the region suggest that the last time the whales were here was around 10,000 years ago.
It was previously thought that the sea ice in the Northwest Passage was too impenetrable even for Bowhead whales, which are known for their ability to navigate ice-bound seas.
The team says the discovery has huge implications for the ecology of marine life in the region.
"[The findings] are perhaps an early sign that other marine organisms have begun exchanges between the Pacific and the Atlantic Oceans across the Arctic," they say.
"Some of these exchanges may be harder to detect than bowhead whales, but the ecological impacts could be more significant should the ice-free Arctic become a dispersion corridor between the two oceans."
Earlier this year, researchers from the NIOZ Royal Netherlands Institute for Sea Research spotted a single Pacific gray whale off the coasts of Spain and Israel, which was beleived to have got there via the Northwest Passage.
They say that the movement of species along this route could have implications for North Atlantic fishing stocks.