Polarstern sets course for the HAUSGARTEN Arctic long-term observatory

Research expedition continues long-term observations in the Fram Strait, which have documented rapid change in the Arctic Ocean for more than 25 years

[Translate to English:] Einsatz des Bongo-Netzes während ARK-XXV/2
Deployment of the Bongo net during ARK-XXV/2 — Deployment of the Bongo net (Photo: Alfred Wegener Institute / Thomas Soltwedel)

In 1999, the Alfred Wegener Institute launched an ambitious project: the HAUSGARTEN observatory in the Fram Strait between northeast Greenland and Svalbard. Spanning ice-covered waters and extending to depths of more than 5,500 metres, this unique research infrastructure has become a key site for monitoring the impact of climate change on polar marine ecosystems. A special issue of the journal Deep-Sea Research Part II: Topical Studies in Oceanography now brings together key findings from 25 years of research at HAUSGARTEN, underscoring the urgent need for global climate action.

When the research vessel Polarstern departs from Bremerhaven at around 5:00 a.m. on Saturday, 4 July 2026, bound for its next Arctic expedition with 54 scientists and 43 crew members on board, it will be heading to a familiar destination: the so-called AWI-HAUSGARTEN, a long-term ecological observatory in the Fram Strait between Greenland and Svalbard. For more than 25 years, international research teams have operated measurement systems anchored on the deep-sea floor at the site. These must be regularly recovered and replaced, while also conducting oceanographic and biological studies. Thanks to extensive bathymetric mapping, the structure of the seafloor is well known, allowing researchers to precisely determine where specific experiments can be carried out. Changing sea-ice conditions are having an increasing impact on the Arctic and therefore play an important role in these multidisciplinary studies.

“HAUSGARTEN is more than a measurement network – it is a long-term memory of the Arctic,” says Dr Thomas Soltwedel, a biologist and long-standing scientific coordinator of the observatory at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). He is the first author of an editorial and initiator of the current special issue of the journal Deep-Sea Research Part II: Topical Studies in Oceanography, which brings together 25 articles by different authors highlighting key developments in long-term ecological research. “Without this data, we would understand neither the rate nor the scale of the changes occurring at the boundary between the North Atlantic and the central Arctic Ocean.”

AWI Director Hajo Eicken emphasizes: “The Alfred Wegener Institute is rightly proud of this important long-term research. Together with the infrastructure of the FRAM Ocean Observing System, HAUSGARTEN provides information that allows us to place Arctic environmental change in a global context. Only fundamental measurements that capture both seasonal variability and year-to-year changes make it possible to identify long-term trends. This helps us understand the impacts in the mid-latitudes and provides important reference data for predictive systems.”

[Translate to English:] Experimente im AWI Hausgarten — Experiments at AWI Hausgarten (Photo: Alfred Wegener Institute / Michael Klages)

The Fram Strait is the only deep-water connection between the central Arctic Ocean and the world’s oceans. Here, warm Atlantic currents meet cold Arctic waters – a dynamic that makes the region an early warning system for global change. At the same time, the Arctic is warming twice as fast as the rest of the planet, and the physical consequences alone are already dramatic: in recent decades, sea-ice thickness in the Fram Strait has decreased by up to 40%. Today, much of the sea ice now originates from other parts of the Arctic – a clear sign of changes in the overall Arctic Ocean circulation. In addition, water temperatures in the eastern Fram Strait in particular have been rising steadily and significantly. Since 1999, annual mean values of up to 1.5°C above the long-term average have been recorded.

Further long-term ecological studies show that the composition of phytoplankton has already changed significantly. Among zooplankton, cold-adapted species are declining, while more heat-tolerant species are migrating into the Arctic – with unpredictable consequences for the food web. Changes in the water column also have a direct impact on the seafloor: organic particles sinking from the upper ocean layers provide food for benthic organisms. However, due to the altered plankton composition, less energy-rich material now appears to be reaching the deep sea, with consequences for all inhabitants of the deep-sea floor – a phenomenon that would have remained unknown without the long-term time series. More recently, the data also served as the basis for a Nature publication addressing changes in deep-sea habitats caused by an increasing occurrence of icebergs.

[Translate to English:] Sensoren FRAM — Sensors (Photo: Alfred Wegener Institute / Wilken-Jon von Appen)

The current special issue also addresses the long-term availability of the data: the online repository PANGAEA (https://www.pangaea.de/) has become a central archive for expedition data, images and video material. The majority of all data collected to date, as well as more than 250 scientific publications, are available in an integrated online archive built on more than 25 years of research at the observatory. The author of this chapter is AWI biologist Dr Autun Purser, who oversees the Ocean Floor Observation and Bathymetry System (OFOBS) and has generated much of the photographic material and video content. Dr Purser will also serve as chief scientist on the upcoming Polarstern expedition. He emphasizes the importance of the long-term observatory: “The consistent monitoring of slow processes such as ocean warming, oxygen depletion, acidification, and ice melt, as well as their ecological consequences, requires the collection of data over extended periods. The results are crucial for assessing the impacts of human activities, developing protection measures, and advancing sustainable management strategies.”

The HAUSGARTEN expedition is scheduled to conclude in Tromsø, Norway, on 3 August 2026. The subsequent expedition, which will depart from there, will head to the northeast Greenland coast and into the central Arctic, where it will focus on geoscientific work. Polarstern is expected to return to its home port in mid-October.