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Sparse sea ice, thousands of data points and samples, a surprising number of animals and hydrothermal vents—those are the impressions and outcomes that an international research team is now bringing back from a Polarstern expedition to the Central Arctic. After a four-month-long Arctic season, the Alfred Wegener Institute's research icebreaker is expected to arrive back in Bremerhaven with the morning high tide on Sunday.

When the research icebreaker Polarstern returns to Bremerhaven, tentatively on Sunday, 13 October 2024, the ArcWatch-2 expedition will bring home an up-to-date scientific overview of the Eurasian and Central Arctic. Researchers from 17 countries and 24 institutes have created an extensive dataset encompassing the atmosphere, ocean circulation, sea ice physics, geochemistry and the ecosystem. After the ship's return, the data will be used to gain better insight into the changes in the Arctic as part of the global ocean and climate system.

According to Prof Benjamin Rabe, chief scientist on the ArcWatch-2 expedition and a physical oceanographer at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), "Compared to the long-term mean, we observed unusually sparse ice cover in the Central Arctic, though the conditions were similar to what we saw during last year's ArcWatch-1 expedition. Now our analyses will focus in part on how this is connected to the other aspects we investigated: the atmosphere and ocean circulation."

The latter is also changing, as Dr. Céline Heuzé, a physical oceanographer at the University of Gothenburg, reports, "A first look at the preliminary temperature and salinity data indicates changes in the circulation of Atlantic water, though this still needs to be confirmed with an analysis of the fully calibrated data."

The oceanographic analyses will be combined with another focus point on the expedition: marine chemistry. The corresponding working groups gathered data on e.g. trace metals, which are also vital for marine organisms. The team also investigated anthropogenic material input, carbon in the form of various compounds, nutrients, and pollutants like mercury. This will make it possible to assess chemical changes in the depths of the Arctic Ocean that satellites can't detect.

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