CONTRASTS (PS149)
Contrasts of sea ice regimes in the Arctic Ocean during melt season
The Polarstern expedition CONTRASTS (2 July to 1 September 2025, also named PS149, ArcWatch-3) investigates the causes and consequences of sea ice melt in three contrasting sea-ice regimes as functions of atmospheric and oceanographic conditions:
1) seasonal sea ice, mostly originating from Russian shelf regions and drifting along the marginal ice zone
2) first- and second year sea ice from the central Arctic Ocean, drifting along the transpolar drift system, and
3) multi-year ice in the “last ice area” north of Greenland.
The overall objective is to characterize the key processes that determine the observed sea ice, ocean, and ecosystem changes in the Central Arctic Ocean during meltseason. The process studies and continuous observations of CONTRASTS will enable us to improve our understanding of linkages between the sub-systems, better quantify ongoing changes with their causes, and to discuss possible future impacts. Impacts are expected on the physical, ecological and biogeochemical systems.
Coordinated measurements of key parameters are performed in the three ice regimes. The work in each regime is centered around ice stations, which are re-visited after 3 and 6 weeks. The on-site work allows intensive measurements, sampling and maintenance. In parallel, multi-disciplinary time series data are recorded by autonomous stations in each regime. The aircraft campaign IceBird summer 2025 complements with regional surveys.
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Associated colleagues at AWI
Benjamin Rabe
Morten Hvitfeldt Iversen
Sandro Dahlke
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The overall objective of CONTRASTS is to characterize the key processes that determine the observed sea ice, ocean, and ecosystem changes in the Central Arctic Ocean during melt season. We will investigate the causes and consequences of differences in sea ice melt in three contrasting sea-ice environments as functions of atmospheric and oceanographic conditions. We will quantify the relative importance of key processes in each region and evaluate their role in the annual cycle of the sea ice cover of the Arctic Ocean. This will enable us to improve our general understanding of the observed changes, their causes and possible past and future impacts, including impacts on the ecological and biogeochemical system. A better process understanding will help to develop new and improved parameterizations, including descriptions over different temporal and spatial scales.
Sea ice physics
The main objectives of the ice physics work are (1) the definition of sea-ice regimes and their characteristics in today’s Central Arctic Ocean, (2) a comprehensive characterization of the physical properties of sea ice, its surface properties, and melt ponds in each regime, (3) the continuation of sea-ice thickness time series, as one of the Essential Climate Variables (ECVs) and a strategic long-term observation, and (4) a better understanding of key processes during melt season to quantify their role for sea ice mass and energy budgets.
Ocean physics
The main objectives of the ocean physics work are both (1) extensive meso-scale surveys, including autonomous instrumentation and helicopter-assisted manual surveys, around each planned ice station, as well as local (2) measurements of turbulence in the water column and right under the sea ice, as well as processes associated with leads and the ice floe edge. Studying the strong links of ocean physical processes to the ecosystem and biogeochemistry will be facilitated by this multidisciplinary expedition.
Atmospheric sciences
The atmospheric program is very much focused on the direct interactions between the atmosphere and the variable surfaces in the central Arctic. The main scientific objectives are (1) Quantify the atmosphere-surface exchanges that impact the sea ice energy and mass budgets, the upper ocean mixed-layer heat budget, and other key bio-physical processes in the ocean-ice system. (2) Understand the drivers of variability in atmosphere-surface exchange processes and how these might be sensitive to the underlying ice and ocean properties. (3) Develop process-based model diagnostics from the observations at the three primary sites and their associated spatio-temporal variability.
Ecology and biogeochemistry
The overarching aim of ecological and biogeochemical research within the ArcWatch program is to analyze the distribution of organisms, biodiversity and ecosystem functions in relation to environmental drivers in the changing Arctic physical-chemical-biological system. During CONTRASTS, we will investigate species abundances, biodiversity and biological and biogeochemical processes and aim to (1) Compare the taxonomic composition, functional community structure and biodiversity, (2) Quantify and compare key ecosystem functions and biogeochemical processes, (3) Compare the trophic connection between the sea ice and the mesopelagic realm, and (4) Investigate processes controlling recruitment and priming winter survival in ecological key taxa.
The CONTRASTS observational concept is a new observational concept, embedded into the ArcWatch expedition series and based on the MOSAiC experience. This expedition will add the sea-ice regime dimension to the ArcWatch and MOSAiC work, as it includes the multi-year and old ice (Region 3) and the marginal ice zone (Region 1) and is realized in a different year with different atmospheric conditions. It is realized in a similar time of year as the related expeditions, but at the same time, closes the observational gap during the peak of melt season, which was missed during MOSAiC due to the break-up of the floe and the rotation between Legs 4 and 5 (28 July to 20 August) and is earlier in the year than ArcWatch-1 and ArcWatch-2 (both early August to early October).
A key element of the work program is a common focus and objective of all groups, to describe contrasts, gradients and transitions between sea-ice regimes (incl. the according ocean and atmosphere conditions, see above). We will perform process-driven bio-physical studies, which are identical in each regime and thus study the melt season in all regimes with the same team, methods, and foci by the same team in one year (summer). This will provide the best possible comparison and then advance our understanding of summer processes and the role of diminishing and surviving sea ice in the Central Arctic Ocean.
Repeated visits to drift stations
The core element of CONTRASTS are main sea ice stations in all three contrasting regions. We will select a representative floe in each region and install ice camps on each floe. We will spend 2-3 days on each floe during each of the 3 visits:
- Visit 1 will include initial measurements and the installation of autonomous instruments.
- Visit 2 will repeat the measurements and maintain the autonomous instruments.
- Visit 3 will repeat the measurements again and recover most of the instruments.
In total, we will be able to observe the melt season on each floe over 6 weeks.
On-route measurements and regional surveys
With Polarstern, the helicopters and also the aircrafts on the IceBird summer expedition (from Station Nord), we observe the gradients and the variability between the three regions. The on-route observations are based on in-situ and remote sensing instruments on the different platforms, measuring complementary atmosphere, sea ice, and ocean properties. As one component, we deploy additional autonomous platforms to form distributed networks in the CONTRASTS regions.
Related programs
- Tara Polar Station is guided into the ice pack and will perform its first measurements in sea ice. The observational program of the platform includes observations of key parameters of the atmosphere-ice-ocean system.
- The Polarstern expedition East Greenland Current Sources (PS150) is realized after the CONTRASTS expedition from 4 September to 23 October 2025. The expedition aims to re-visit ice regime 3 and might realize additional measurements on the same floe and thus exend the time series into freeze-up.
- The IceBird summer 2025 aircraft campaign will fly over the regions and contribute with regional surveys.
- Other research vessels as RV Oden, Kronprins Håkon, and Le Commandant Charcot will study the 2025 melt season in their programs
- The International Arctic Buoy Progam is cooperationg with the deployment of more autonomous instruments
- Side user programs: WISELIGHT, LEAD, and VAMPIRE-2 (see under Participants)
The CONTRASTS expedition is scheduled from 02 July to 01 September 2025 (61 days at sea). As the exact locations of all ice stations as well as the ice conditions are only known once the regions are reached, this schedule is only the basis of planning:
- 02 July: Departure from Tromsø, Norway
- 05 July: Meet Tara Polar Station at the ice edge
- 10 July: Arrival at ice station = Regime 1
- main work at all ice stations and along the transects
- 28 August: complete last station work in Regime 3
- 01 September: Arrival in Longyearbyen, Svalbard
The CONTRASTS program uses all berths on Polarstern (51 scientists, 1 weather service, 4 helicopter crew). The expedition is lead by Marcel Nicolaus and Thomas Krumpen (both AWI) and the work on board is organized in 4 scientific teams:
- Sea ice physics
- Ocean physics
- Atmospheric sciences
- Ecology and biogeochemistry
with additional support for logistics, data, and media work.
The participants (on board and principal investigators on land) are affiliated with:
- Germany: AWI, Universities of Bremen, Bayreuth, Duisburg, Köln, and Oldenburg
- Switzerland: WSL-Institut für Schnee- und Lawinenforschung (SLF)
- United States: Dartmouth College, Woods Hole Oceanographic Institute, U of Washington (APL), U of Colorado
- Japan: Hokkaido University, U of Tokyo
- Norway: Norwegian Polar Institute, Norske Arktiske Universitet (UiT)
- Sweden: Stockholms University
- Taiwan: National Academy of Marine Research, National Sun Hat-sen University
- Finland: Finish Meteorological Institute