The bathymetry team works closely with other research groups on board, for example with physical oceanography. This enabled the scientists to track various water masses along several sections from the deep sea to the continental shelf and investigate the colonisation of the sea floor. In doing so, they gained important insights into the decline of Antarctic deep water in comparison to the long-term data collection that the AWI has been conducting in the region via oceanographic measurements as part of the Hybrid Antarctic Float Observing System (HAFOS) since 2002. In addition, the outflow paths of cold water from the Larsen Ice Shelf have been narrowed down. These water masses have a significant influence on global ocean currents and the melting of sea ice, particularly on the continental shelf.

Unlike the sea ice in the Arctic, the Antarctic sea ice was considered relatively stable for a long time. However, the summer sea ice extent in the north-western Weddell Sea has declined sharply since 2017, presumably as a result of warmer surface water. Prof Dr Christian Haas, head of the Polarstern expedition and AWI Sea Ice Physics, comments on the initial results of SWOS (Summer Weddell Sea Outflow Study): “The ice thickness showed great regional variability. On the western, shallow continental shelf in particular, the ice was up to four metres thick, which we can attribute to strong deformation caused by the tides and the proximity to the coast. The ice further east came from the large Ronne and Filchner ice shelves and was less deformed with thicknesses of around one and a half metres.”

Overall, the sea ice showed surprisingly strong surface melting, which mainly affected the snow cover and the uppermost ice layers and led to almost Arctic conditions, where the ice is covered with many melt ponds. Christian Haas reports: “Although we only found very few melt ponds, the ice was often almost free of snow and had a bluish or greyish surface. Thanks to novel measurements of the water directly under the ice using turbulence and biological probes, we found larger quantities of sweet meltwater in and under the ice. This has a strong effect on the biological colonisation of the ice and the interactions with the seawater under the ice, because such freshwater lenses keep the heat from the ocean away from the sea ice.”

Future analyses and modelling will show what contribution the organisms living in and under the sea ice make to the carbon cycle in the Southern Ocean, for example. However, the researchers will only carry these out after the expedition, which is scheduled to end on the Falkland Islands (Malvinas) on 9 April 2026. From there, the Polarstern will start its transit across the Atlantic and is expected to return to its home port of Bremerhaven in mid-May.

More information about the expedition can be found in the Polarstern App.