Polarstern returns from the Central Arctic Ocean

The LAMEX 1 expedition fills a data gap on the Lomonosov Ridge and brings back sediment cores spanning several glacial cycles

[Translate to English:] Bergung Ozeanbodenseismometer — Recovery ocean bottom seismometer (Photo: Alfred Wegener Institute / Tim Lyons, Chris Lyons, SlingshotPictures)

On 14 October 2026, the research icebreaker Polarstern is due to return to its home port of Bremerhaven from its final Arctic expedition of this summer. The ten-week PS156 (LAMEX 1) expedition took around 40 researchers from Germany, Norway, Italy, Argentina and the USA from Tromsø via north-east Greenland and the Fram Strait to the North Pole and the Lomonosov Ridge. In total, the ship covered a good 9,000 nautical miles (around 16,700 kilometres) to collect data on the geological past, which will enable better projections for our future.

[Translate to English:] Luftpulser — Preparations (Photo: Alfred Wegener Institute / Tim Lyons, Chris Lyons, SlingshotPictures)

The Lomonosov Ridge is an underwater mountain range that stretches across the entire Arctic Ocean. Next to it, the seabed is around 4,000 metres deep; the ridge itself is about 3,000 metres high and thus rises to a depth of 1,000 metres. Very little was previously known about the section between the North Pole and the already well-studied eastern end of the ridge. Here, the scientific team on board the Polarstern measured around 2,200 kilometres of seismic profiles, thereby closing an important gap in the existing data. Using the data now obtained, they can demonstrate how the sediment bodies along the flanks of the Lomonosov Ridge have formed over the course of Earth’s history under the influence of ocean currents.

“We now have continuous seismic data stretching roughly from the North Pole almost all the way to the Siberian shelf,” says expedition leader Dr Catalina Gebhardt, a geophysicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “This links the profiles to the deep borehole that was drilled near the North Pole in 2004 and whose ages we know. This means we can now, for the first time, assign ages to the seismic reflectors and trace them all the way to the Siberian shelf. This helps us to understand when ocean currents changed in the past and whether this coincided with major tectonic or climatic upheavals in Earth’s history.”

[Translate to English:] Proben für fossile DNA — DNA sampling (Photo: Alfred Wegener Institute / Tim Lyons, Chris Lyons, SlingshotPictures)

The geology team has also returned with a rich haul: The team retrieved approximately 108 metres of sediment cores using the gravity corer, in addition to three kastenlot cores. The latter is an exceptional coring device, as it has an impressive cross-section of 30 by 30 centimetres and brings a very large volume of sediment on deck. “This means we have extensive material from the same sediment core to carry out a wide range of analyses. This also enables the use of new methods – ranging from the analysis of cosmogenic nuclides to the investigation of fossil DNA – for which the available sample material is often insufficient in other cores,” explains co-expedition leader Dr Juliane Müller, a marine geologist at the AWI. The cores span several glacial–interglacial cycles and thus include, amongst other things, the particularly warm last interglacial period. They are intended to reveal what environmental conditions and the Arctic ecosystem were like in the past. This also provides insights into how the Arctic might change as human-induced warming progresses.

The oceanography team investigated ocean currents along several profiles – mostly across the Lomonosov Ridge – using 106 CTD measurements. The ridge is a major bathymetric barrier in the Arctic Ocean and thus influences water circulation. The researchers wanted to know how currents flow along and across the ridge today – and whether, at points where the ridge is more deeply incised, there is an exchange of water masses between the eastern and western parts of the Arctic.

Right at the start of the expedition in mid-August, the expedition team recovered four ocean-floor seismometers in the Fram Strait and dismantled and serviced land-based stations on the 79°N glacier off north-east Greenland. These stations use high-precision GPS sensors to measure how the world’s largest island behaves as its ice cover decreases. With the loss of vast glacial ice masses, there is less pressure on Greenland, causing the island to rise – a phenomenon the researchers were able to confirm with their new data. Some of the land-based stations also measure earthquakes – and at the same time, they monitor tremors caused by ice, for example when glaciers slide over the rugged Greenlandic terrain. Two moorings were recovered off Flade Isblink, an ice cap in the far north-east of Greenland. The sea ice in north-eastern Greenland was unusually dense in the summer of 2026, preventing further work in the region.

The voyage was also something special from the ship’s perspective: On 26 August, the Polarstern passed the two-million-nautical-mile mark since entering service in 1982, and on 4 September it reached the North Pole for the ninth time.

The samples and data are now being analysed in the laboratories at the AWI and at partner institutes. They are intended to reveal how ocean currents and sea ice have changed during previous warm periods – and how quickly. This is also important for Europe: the Arctic Ocean is where the cold, salty water originates that sinks in the North Atlantic and drives the ocean circulation to which Europe owes its mild winters. Reports from the expedition can be found in the weekly reports and on the Polarstern app.

Over the coming month, the Polarstern will be at the Lloyd shipyard in Bremerhaven for routine maintenance and repair work. The transit to Antarctica is scheduled to begin in mid-November, during which young researchers will receive training. The icebreaker will then resupply the Neumayer III station in Antarctica before carrying out two expeditions in West Antarctica.