“Accordingly, we found hardly any ice algae on the underside of the sea ice. Especially Melosira arctica was missing, which can form metre-long chains and is an important nutrient supplier for the entire ecosystem. The ice looked rather dead this year. Due to the darkening by snow, algae floated up from the water and formed a film under the ice, to get some light,” reports chief scientist Prof. Dr Antje Boetius, Director of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). The physical oceanographers on board also discovered changes in the uppermost ocean layer, which was saltier than in previous years, due to the lack of ice melt and to lower inputs of Siberian shelf water.
The comparison with the previous survey years 2012 and 2020 also showed differences for the planktonic life floating in the water. In August and September, the algal bloom was long gone, and no ice algal biomass built up under the ice. Instead, the researchers found swarms of animals such as arrow worms, tunicates, ice amphipods, copepods, winged snails and comb jellies. The team led by the expedition co-leader Dr Christina Bienhold therefore found the biotic communities in the deep sea had changed: “Hardly any ice-algae sank into the deep sea this year. Nevertheless, the overall activity of living organisms on the bottom has increased somewhat compared to the sea ice minimum in 2012.” Images taken with a deep-sea camera showed that the composition of the community has changed substantially. The once smooth seafloor became heavily colonised and burrowed by annelids and bristle worms, crawling sea anemones and sea cucumbers. “It is amazing how quickly Arctic life responds to changes in sea ice cover,” says Antje Boetius. The team was able to obtain samples of all size classes of life in the Arctic deep-sea to study their diversity and distribution as well as changes compared to past decades.
The research of the ArcWatch-1 expedition also included seafloor mapping of previously unknown seamounts, one of which turned out to be a biodiversity hotspot. In addition, the chemists on board obtained large quantities of water and ice samples to record changes in the carbon pump to the deep sea and to detect non-degradable chemicals. For a European project, they are assessing the distribution of pollutants in the Arctic. The Polarstern team also successfully deployed a range of new high-tech instruments such as robots, autonomous sensors and sampling modules, and high-resolution under-ice cameras. They built a large network of buoys and deployed novel moorings for year-round surveys. This will provide them with further data on the changes in the central Arctic Ocean, even after Polarstern now returns from the central Arctic.