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Climate

Ice algae sink onto seafloor as the Arctic warms

Global warming is affecting deep Arctic Ocean ecosystems much faster than scientists expected. Ice algae have started sinking down to the seabed, altering the food web and the oxygen content of the waters.

Ice algae thrive underneath the sea ice of the central Arctic. They are important producers of food and oxygen in this fragile ecosystem. But what happens to these ice-dependent algae as climate change melts the ice?

Die Probenaufbereitung erinnert ein wenig an den Sandkasten. Tiefseeforscher finden im Schlamm aus mehreren Tausend Metern Wassertiefe Seestern, Seegurken, Krebse und viele andere Tiere. Foto: Antje Boetius, Alfred-Wegener-Institut.

AWI researcher examines deep-sea samples on board the 'Polarstern'

Professor Antje Boetius was surprised by the answer she found during a scientific cruise last summer aboard the German research vessel Polarstern, owned by the Alfred-Wegener Institute for Polar and Marine Science (AWI). Boetius, who heads AWI's Deepsea Ecology and Technology team, spent two months in the central Arctic. That summer the sea ice declined to a record extent.

Green carpet on the ocean floor

The researchers discovered that the melting ice on the surface was affecting conditions down to a depth of 4,000 meters.

"We took a look at the sea floor and found that most of the ice algae which form thick carpets under the ice had dropped right down into the depths when the ice melted," Boetius said in an interview with DW.

"We travelled through a very wide area of the Arctic and found that this process was happening everywhere. We also found out that only a few lifeforms in the Arctic Ocean can actually make use of these algae as food. For the most part, they lie around on the ocean floor and are attacked by bacteria."

The problem, the scientist explains, is that this uses up large amounts of oxygen. The team found areas of the seabed where the oxygen supply had been depleted.

An ocean in transformation?

The scientists concluded that the ice algae has started growing faster than usual because the thinner ice is letting much more light through. At the same time, the thinner and warmer ice melts faster, releasing the algae, causing it to sink to the bottom.

"For the first time we are able to demonstrate that the warming and related physical changes in the Arctic are causing fast reactions throughout the ecosystem," Boetius explained. It was previously assumed that deep sea areas would not immediately be affected by global warming.

Cucumber of the genuis Kolga feeding on ice algae. Photo: Antje Boetius, Alfred Wegener Institute.

Found on the sea floor, the sea cucumber is one species that feeds on the algae.

Boetius said it remains unclear if this is just a one-off occurrence or whether "we are seeing the new Arctic, as it will be in the future." Scientists intend to keep collecting data in the years to come.

"Perhaps the Arctic will be a completely different ocean in five years. Our observations support that possibility," Boetius added. The marine expert said the consequences should be evident. If global warming can change an ocean system this quickly, faster action is needed in order to keep climate change in check.

DW.DE