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In the Arctic: View of ice and sea from the "Polarstern"

Photo: Esther Horvath / dpa

Researchers at the Alfred Wegener Institute (AWI) in Bremerhaven spent two months sailing an icebreaker towards the North Pole. They noticed something special: In August and September, there was an unusually large amount of snow on the sea ice, said Marcel Nicolaus, sea-ice physicist at the AWI this Friday.

"The Arctic sea ice is actually characterized by the fact that there is no more snow on it in summer and it is covered with ponds," Nicolaus said at an online press conference. One explanation for the phenomenon is unusually stable low-pressure systems in summer. They would have provided cold polar air in the Arctic and held the ice of the Siberian shelf together.

The press conference was broadcast from aboard the research vessel "Polarstern". Nicolaus was on the road with a research team led by AWI Director Antje Boetius to measure the sea ice. The ship is expected back in Bremerhaven on Saturday.

»The snow saved the ice«

In view of the record global summer of 2023 and the rapid melting in May and June, the researchers had expected particularly little sea ice in the Central Arctic. Instead, the ice thickness was around 1.2 meters – more than in the strikingly bad years of 2020 and 2012.

"That was extraordinary," said Nicolaus. "The snow saved the ice." He had protected it from surface melting.

At the same time, unlike usual, hardly any ice algae have formed on the underside of the sea ice. "Melosira arctica in particular, which can form meter-long chains, was missing," Antje Boetius said, according to a statement. The ice looked completely different from the years before, "it was dead, so to speak."

In the past, entire algae forests would have hung under the ice. These serve as a source of nutrients for the underwater ecosystem. "Because of the darkening caused by snow, algae floated out of the water and lay down under the ice in a film to get some light," the expert continues.

At the beginning of April 2023, a study by the AWI showed that large amounts of microplastics accumulate on algae in the Arctic. Specimens of Melosira arctica contained ten times as many particles as the surrounding seawater. This poses a danger to living beings that feed on the algae, it said. The samples examined at the time came from an expedition in the summer of 2021.