- The Polarstern expedition CONTRASTS (PS149) will delve into the causes and effects of sea-ice retreat in the Arctic Ocean
- Field work will focus on the different melting behaviours of different types of sea ice
- This will be supplemented by regional observations: simultaneous aerial survey flights as part of the IceBird summer campaign
Figure 1: Logo of the CONTRASTS Expedition (Graphic: Marcel Nicolaus, Alfred Wegener Institute)
RV Polarstern expedition will put the spotlight on sea ice
Based on ten years of planning, the RV Polarstern expedition CONTRASTS (PS149) will focus exclusively on sea ice, addressing a number of related questions. Cruise leader Dr Marcel Nicolaus, a sea-ice physicist at the AWI, explains its goals as follows:
Through the CONTRASTS expedition, we will deepen our understanding of interactions between the ocean, atmosphere and sea ice. In particular, we want to better understand which sea ice survives the summer melting, and which doesn’t. Then we can quantify the current changes and better predict potential future developments. Our goal is to more fully understand the role of the melting and surviving sea ice in the Arctic summer. This will ultimately allow us to make better forecasts for future developments in the Arctic.
The expedition will begin when RV Polarstern weighs anchor in Tromsø, Norway, on 2 July 2025 and end when she enters port in Longyearbyen, Svalbard, on 1 September 2025. As part of an international collaboration, at the start of the expedition RV Polarstern will also transport the new French research platform Tara Polar Station to the sea ice north of Svalbard for its first expedition (Fig. 2).
Figure 2: Planned cruise track (red line) with the three targeted sea-ice regimes (green stars, R1 to R3). It is planned to visit each regime three times during the expedition. As the sea ice drifts, the location of each regime will change, too. The aircraft campaign IceBird-Summer flies out of Station Nord on Greenland. The background map shows the exemplary sea ice concentration in August 2024. (Graphic: Marcel Nicolaus, AWI)
The CONTRASTS team on board will consist of 51 scientists from 14 nations, who represent institutes from eight countries. Many members of the consortium already successfully collaborated during the MOSAiC expedition (2019/20) and ArcWatch-1 expedition (2023).
In July and August 2025, parallel to the Polarstern expedition, the IceBird summer campaign will be underway. Launching from the Danish military base Station Nord in Greenland, the research aircraft Polar 5 will fly over the CONTRASTS regions and stations, gathering large-scale sea-ice observations and identifying regional gradients in the ice thickness. “As such, there will be two sea-ice expeditions in the summer of 2025 that are optimally complementary,” says co-cruise leader Dr Thomas Krumpen, a fellow sea-ice physicist at the AWI.
Investigating different sea-ice regimes
The RV Polarstern expedition will concentrate on the differences – or contrasts – between different sea-ice regimes, and on gaining a better understanding of their connections to oceanographic and atmospheric parameters. The observations will focus on three sea-ice regimes:
1. Seasonal sea ice, which was formed last winter and frequently drifts along the sea-ice margin zone – the ice regime that will most likely dominate the summertime Arctic in the future.
2. Two-year-old sea ice, which flows across the Arctic Ocean with the Transpolar Drift – the ice regime that is characteristic of the status quo in the Arctic.
3. Multiyear sea ice, which has drifted for years north of Greenland and Canada, hailing from the “last ice zone” north of Greenland – the ice regime that was still common several decades ago.
As Thomas Krumpen adds: “We expect to find that the sea ice’s age and provenance have major influences on its physical and biological characteristics. For instance, older ice is thicker and more deformed. Drawing on a range of satellite and model-based data, we can identify the different ice-age zones in advance, allowing us to travel directly to them during the expedition” (Fig. 3).
Figure 3: Evolution of sea-ice age (from 1 to 5+ years) in the study area between January 2024 and June 2025. Sea -ice age information is provided by the National Snow and Ice Data Center (NSIDC). We gratefully acknowledge Scott Stewart, Mark Tschudi, and Walt Meier for providing accelerated access to the data during our field experiment. (Graphic/Animation: Thomas Krumpen, Alfred Wegener Institute)
A journey through space and time
The central elements of the CONTRASTS expedition are sea-ice stations in all three aforementioned ice regimes. In each region, a representative floe will be selected, and an ice camp will be set up on its surface. In the course of three visits of two to three days each, every floe will be intensively surveyed. During the first visit, monitoring devices will be installed on, in and below the sea ice, which will then autonomously observe the melting season (Fig. 4). The time series they produce will ensure continuity for the duration of the expedition, even when the team is busy working in one of the other regimes. This approach will allow the experts to observe the melting season on each of the three floes for roughly six consecutive weeks. During the second visit (after ca. three weeks), routine maintenance will be done on the monitoring systems; during the third (after ca. six weeks), most of the instruments will be retrieved and only a few will be left behind as drift buoys. Their sensors will in turn make it possible to continue monitoring the floes’ drift and development in the freezing phase, after the expedition ends. “Right now, we’re hoping that we can return to at least one of the stations, take samples and survey it during the subsequent expedition, “East Greenland Sources” (PS150), which will go from 4 September to 23 October 2025. That would be the icing on the cake for our expedition,” says Marcel Nicolaus, who will also be on board for the second expedition.
Figure 4: Possible sea-ice conditions at the three sea-ice regimes during CONTRASTS. The figure is composed of photographs from previous expeditions, showing surface and under-ice impressions of different sea-ice types. (Graphic: Marcel Nicolaus, Alfred Wegener Institute)
The observational approach that will be pursued on CONTRASTS – dividing the sea ice in three regimes – is new and entails particularly close integration of intensive, repeated manual measurements and autonomous time series. The methodology and team structure are based on lessons learned during 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.
One central goal: the combined analysis of contrasts, transitions and gradients between the sea-ice regimes – including the corresponding status quo of the ocean and atmosphere. The CONTRASTS team will conduct standardised, process-based biophysical tests in all regimes so as to arrive at comparable results.
Teamwork between physics and ecology
Overall, the CONTRASTS expedition will establish a multidisciplinary platform for studying physical and biological processes alike (Fig. 5 and Fig. 6). The work on board will be divided between four teams:
- The sea-ice physics work will focus on systematically defining the different sea-ice regimes in the Central Arctic and comprehensively characterising their physical properties, surface structures and meltponds. It will especially focus on continuing long-term time series on ice thickness, which is widely considered to be one of the essential climate variables (ECVs). In addition, central processes will be analysed during the summer melting phase in order to better quantify their influence on the sea ice’s energy and mass balance.
- The ocean physics tests will include both meso-scale surveys – using autonomous systems and helicopter-assisted manual readings – of the three planned ice camps and their vicinities, and local measurements of turbulence in the water column and directly below the sea ice. Special attention will be paid to processes in connection with floe margins and leads. The data gathered will ideally help clarify the relations between physical processes in the ocean on the one hand and ecological and biogeochemical systems on the other – an objective that the expedition’s multidisciplinary approach will help to achieve.
- In terms of atmospheric research, the experts will concentrate on direct exchange processes between the atmosphere and ice surface. Here, the goal is to quantify those interactions that have the greatest influence on the sea ice’s energy and mass balance, and on the upper layers of the ocean. In addition, the processes that determine the variability of these exchange mechanisms will be analysed. On the basis of the observations made at the three ice camps, improved process descriptions for numerical models will be developed after the expedition, in order to more accurately reflect the temporal and spatial variability of atmospheric influences.
- The ecology and biogeochemistry work will address the question of how biodiversity, species distribution and ecosystem functions develop when influenced by physical and chemical changes, also and especially in the melting season. The focus will be on comparative analyses of the taxonomical composition, functional structure and biodiversity of biological communities in the respective ice regimes. Further, the team will quantify central ecosystem processes and biogeochemical cycles and investigate the trophic connections between sea ice on the surface and seawater to a depth of 1000 m (the “dysphotic zone”). Lastly, they will identify processes that are essential for the recruitment and survival of ecologically relevant species in winter.
We at meereisportal.de are also excited about CONTRASTS, which promises to be a truly unique expedition. Accordingly, we’ll be accompanying it with extensive coverage and the latest data, photos and live-cams at: www.seaiceportal.de/contrasts
Figure 5: Ice station work during the MOSAiC expedition in summer 2020. Exemplary for the ice camps of CONTRASTS, this illustrates the combined investigations by in-situ measurements, autonomous stations, airborne operations and measurements from RV Polarstern. (Photo: Marcel Nicolaus, Alfred Wegener Institute)
Figure 6: Conceptual layout of the ice camps of CONTRASTS. The vessel RV Polarstern (blue shape) is anchored to the ice floe (grey area). Different observations cover overlapping areas to measure bio-physical properties of atmosphere, sea ice, and ocean properties. Deployment sites (light orange boxes) indicate regions for autonomous stations that stay behind while the vessel with the teams is working in other regimes. (Graphic: Marcel Nicolaus, Alfred Wegener Institute)
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