Iversen had brought a new kind of camera system on board. Supported by artificial intelligence, he can use it to count how many algae are present in a certain sample. The marine biologist was hoping the technique would show the development of the ice algae population during the summer in real time.

His first great surprise came on Floe 1: "Zero" was the algae count he received. Iversen thought it was an outlier, perhaps the result of the ice beginning to melt particularly early this year. Maybe the algae had already separated from the ice, he thought.

But he found the same result on Floe 2 and Floe 3. In other years, the ice algae had grown like thick grass on the underside of the floes, even coloring the ice entirely in some areas. But this year, Iversen found nothing. He was also unable to find any algae floating in water where it should have been present. Typically, they form small gas bubbles that keep them afloat for a long time after separating from the ice.

The ice algae is essential for the Arctic ecosystem, as analyses performed by AWI scientists have shown. In the fall, when the seawater freezes, the algae is frozen into the ice off the Siberian coast. Only when light begins penetrating the ice after the polar night comes to an end does the algae bloom, forming long filaments stretching for up to several meters with which they can filter the scarce nutrients from the water.

These algae mats provide nourishment to sea butterflies, amphipods, copepods and other miniscule creatures, with their footprint found throughout the food chain, even into the depths of the ocean. AWI research has found that much of the carbon in the Arctic Ocean is funneled into the ecosystem through the ice algae. They are the organisms that keep the life cycle in the ice-locked sea going.

Once the North Pole becomes ice free, as ecologists have long been saying, the ice algae underneath the ice will also disappear. And the ecosystem will collapse. But might it be that this future scenario has already become reality?

A former Polarstern expedition already gathered evidence two years ago of a dramatic reduction in the amount of ice algae. Now, Contrasts appears to have confirmed this finding.

Iversen is still hesitant about speaking of an ecosystem collapse. He first wants to examine the sediment samples he took from the ocean floor 4,000 meters below the surface. He wants to know if he might find evidence there of freshly sunken algae.

But Iversen does think it possible that the ice-free future may already have begun for the Arctic environment. And he has already taken a look at how this future might look. In sediment traps suspended beneath the ice, large quantities of tiny fecal pellets have accumulated. They come from pteropods, small marine animals that filter bacteria from seawater while encased in a gelatinous coating. They seem to be the big winners of the ongoing ecological transformation.

Iversen sees them as a reassuring message. "Nature," he says, "always finds a way."

Expedition to the North Pole: Polar Researchers Fear an Ecological Collapse in the Arctic