By Jonathan Amos BBC Science Correspondent
The German Research Vessel Polarstern has sailed back into its home port after completing a remarkable expedition to the Arctic Ocean.
The ship spent a year in the polar north, much of it with its engines turned off so it could simply drift in the sea-ice.
The point was to study the Arctic climate and how it is changing.
And expedition leader, Prof Markus Rex, returned with a warning. “The sea-ice is dying,” he said.
“The region is at risk. We were able to witness how the ice disappears and in areas where there should have been ice that was many metres thick, and even at the North Pole – that ice was gone,” the Alfred Wegener Institute scientist told a media conference in Bremerhaven on Monday.