Journey through space and time

The latest Polarstern expedition is off to explore ice floe types from the past, present and future

Buoy Installation (Photo: Folke Mehrtens)

On Wednesday, 2 July 2025, the Polarstern will set sail from Tromsø, Norway, embarking on an expedition to the Arctic Ocean. Over the next two months, an international research team will analyse the feedback effects between global warming and sea ice retreat in the Arctic Ocean. The investigations will focus on the differences in the melting of various sea ice types – representing the Arctic of the past decades, the present and the future. A parallel airborne campaign will complement the measurements and, at the outset of the expedition, the Polarstern will support the first ice testing of the new French Tara Polar Station research platform.

There are still three different regimes of sea ice in the Arctic Ocean, while global warming is causing older and therefore thicker ice floes to melt increasingly. The current Polarstern expedition is focussing on three different ice regimes: one-year-old sea ice, which formed last winter – often drifting in the sea ice marginal zone and expected to dominate the Arctic in the future. Two-year-old sea ice drifts over the polar ice cap along with the Transpolar Drift before melting in the Fram Strait and is characteristic of the present status quo. Multi-year sea ice has been drifting north of Greenland and Canada for years, originating from the so-called "last ice area" north of Greenland and was still widespread decades ago.

[Translate to English:] PS138 — Ice anchor (Photo: Alfred-Wegener-Institut / Esther Horvath)

The Polarstern team is setting up observation networks and collecting data on three ice floes representing these regimes. The disciplines and measuring instruments involved are similar to the MOSAiC expedition , during which the Polarstern drifted through the Arctic Ocean for over a year from 2019 to 2020, investigating an ice floe consisting mainly of one- and two-year-old ice. On the current expedition, dubbed CONTRASTS, the researchers will investigate in far greater detail the contrasts, transitions and gradients between the three sea ice regimes, including the associated ocean and atmospheric conditions, as well as the biology and biogeochemical processes taking place.

"We are especially focused on gaining a better understanding of which sea ice survives the melt in summer and which type does not. This is due to the fact that the Arctic is warming particularly quickly compared to the rest of the world, and warm air and water temperatures are impacting on the ice both from above and below," says Dr Marcel Nicolaus, explaining the motivation behind the Polarstern expedition. The sea ice physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) is leading the expedition named CONTRASTS, and coordinating a 51-member strong team of international scientists. He goes on to add: "With the CONTRASTS expedition, we will deepen our understanding of the interactions between the ocean, the atmosphere and sea ice. This will allow us to quantify current, ongoing changes and better assess possible future developments. We aim to better understand the role of the disappearing and remaining sea ice in the Arctic summer, thereby also enabling us to better predict future developments in the Arctic."

[Translate to English:] Buoy Installation — Buoy Installation (Photo: Folke Mehrtens)

The sea-ice stations situated in the three ice regimes represent the central elements of the CONTRASTS expedition. A representative floe will be selected in each region and fitted out with an ice camp. Each floe will be visited three times for two to three days each, and will be intensively surveyed. During the first visit, measuring devices will be installed on, in and under the sea ice, which then monitor the melting season autonomously. Around three weeks later, the second visit will allow the systems to be maintained, while on the third visit (after about six weeks) most of the devices will be dismantled again, leaving only a few instruments remaining behind as so-called drift buoys. Among other things, these remaining sensors transmit precise position data so that either the Polarstern on a subsequent expedition or other research institutes can recover them later. In this way, it is possible to follow the drift and development of the floes into the freezing phase following the expedition. The CONTRASTS team will be carrying out standardised, process-based bio-physical investigations in all regimes in order to achieve comparable results.

This observation approach CONTRASTS is pursuing – dividing the sea ice into the three regimes – is entirely new, and entails the particularly close integration of intensive, repetitive, manual measurements and autonomous time series. The methodology and team structure are based on the experience gained from the MOSAiC expedition. "In this way, our MOSAiC datasets can now be expanded to include the dimensions of the different ice regimes as additional information. Moreover, we can specifically take our readings during the highest melting phase, something that couldn’t be completely achieved during MOSAiC for logistical reasons," explains Marcel Nicolaus.

Running parallel to the Polarstern expedition, the IceBird summer flight measurement campaign will also be underway in July and August 2025. Launching from the Danish military base Station Nord in Greenland, the AWI Polar 6 reseach aircraft will fly over the CONTRASTS regions and stations to record the sea ice over a large area and map regional gradients in the ice thickness. "In the summer of 2025, we will conduct two coordinated sea-ice expeditions by ship and by aircraft, which are designed to map local to regional scales," as Dr Gerit Birnbaum, AWI sea-ice physicist, outlines. As the head of the flight campaign explains: "We expect the age and origin of the sea ice to have a significant influence on the physical properties of the sea ice and the associated organisms. Old ice, for example, is more deformed, more structured and less translucent. We were able to identify the zones of different ice ages in the run-up to the expedition by way of various satellite and modelling data, and the Polarstern will now be heading specifically to these zones."

The Polarstern will also be supporting the French Tara Polar Station research platform at the outset of the expedition. In the future, the new vessel will drift through the Arctic on one-year campaigns and will complete its first ice trials in the summer of 2025. To this end, the Polarstern will accompany the Tara Polar Station from Longyearbyen (Svalbard) on its way north. The CONTRASTS expedition is also scheduled to wind down in Longyearbyen on 1 September 2025.

Further information:

Departure is planned for early evening today, and the Polarstern's current position can be tracked via live camera: awi.panomax.com

In addition to the Polarstern app (https://follow-polarstern.awi.de/), there is also an interactive CONTRASTS website featuring live footage from the Polarstern and the three ice camps: https://data.meereisportal.de/relaunch/contrasts

Further background information on the teamwork between physics and ecology on the CONTRASTS expedition is available here on the Alfred Wegener Institute's sea ice portal: https://www.meereisportal.de/newsliste/detail/contrasts-meereis-expedition-untersucht-das-schmelzende-arktische-meereis

Tara Polar Station: https://www.awi.de/en/science/climate-sciences/sea-ice-physics/main-research-foci/translate-to-english-tara-polar-station.html