- The Baltic: In the course of a prolonged frost period, the bodden along Germany’s Baltic coastline froze over. In Bothnian Bay, the northernmost part of the Baltic Sea, the fast ice in the archipelago reached thicknesses of up to 65 cm.
- The Arctic: In January, too little new sea ice was formed to compensate for the deficits in the preceding winter. One cause could be the enormous amount of heat absorbed by the ocean in 2025.
- The Antarctic: The summer sea-ice melting on the Southern Ocean slowed significantly in January. But in the northwest Weddell Sea, the target region for an upcoming Polarstern expedition, there is currently more pack ice than anticipated.
Frigid winter temperatures freeze over bodden of the Baltic Sea
Ice floes in the southern Baltic Sea, and therefore also on the German coastline, have become a rare natural phenomenon. It was therefore all the more surprising when, at the beginning of the new year, a frigid winter high-pressure cell formed over the Baltic Sea and stayed there. “In the vicinity of Usedom and Rügen, there was prolonged frost on nearly half of the days of January, which caused the Greifswald Bodden to freeze over for the first time in five years,” reports Wiebke Aldenhoff from the Ice Service of the Federal Maritime and Hydrographic Agency (BSH) in Rostock (Figure 1).
The Ice Service team gathers all available data on the ice conditions along the German coastline and analyses it on a daily basis – not just satellite data, but also eyewitness accounts from port authorities, sailors and other seafarers, and ice observers. They subsequently share these analyses with shipyards, the Federal Waterways and Shipping Agency (WSV), and other interested parties from the shipping sector. “The majority of our clients want to know where the ice is. How far can I go with my ship? Is my destination port still ice-free, or are there restrictions along my planned Baltic Sea route, like no night navigation because piloting through the ice by sight is no longer considered safe?” Wiebke Aldenhoff explains.
Once a week, the team prepares a high-resolution ice map for the entire Baltic Sea, which is supplemented by the daily ice maps provided by their colleagues at the Swedish and Finnish ice services (Figures 2 & 3). “We also map the small patches of ice that aren’t on the shipping lanes, since this information could someday be relevant for marine and climate research,” the physicist relates.
Figure 1: View of the ice-covered Greifswald Bodden near Hof Gronow. The first ice floes have already stacked up on the shoreline. Taken on 31 January 2026. Photo: Bärbel Weidig
Figure 2: This map from the BSH Ice Service shows the sea-ice concentration in the Baltic on 30 January 2026. As the colours clearly show, Bothnian Bay (northernmost part) and the Gulf of Finland (easternmost part) alike were already largely covered by solid sea ice. Map: BSH Ice Service
Figure 3: This map from the BSH Ice Service shows the sea-ice thickness in various regions of the Baltic. In the northernmost part of the Gulf of Bothnia, Bothnian Bay, the fast ice attached to the coast was up to 65 centimetres thick (bright green). In the bodden along Germany’s Baltic coast, the maximum thickness only reached 15 centimetres (violet). Map: BSH Ice Service
From our webcams in the Bay of Pomerania, for instance, we can see a great deal of stacked-up ice slush along the coast; because of the cold east wind, floes don’t form on the Baltic Sea. The slush then drifts to the coast and into the Greifswald Bodden, where it freezes into sea ice. On the last day of January, Szczecin Lagoon was also covered with a layer of solid ice (Figures 4, 5 & 6).
As a rule, the lagoon and the bodden of the eastern part of Germany’s Baltic Sea coast are the first to freeze over. This is due to their high degree of freshwater intake, low depth, and often sheltered positions. The strait between Rügen and the island Hiddensee also often quickly freezes over, as does the Schlei, a 42-kilometre-long inlet on the Baltic Sea coast of Schleswig-Holstein. “In some sheltered stretches of coastline, we’re currently seeing ice thicknesses of up to 30 centimetres. And as long as we continue to have consistent frost at night, the ice can continue to grow,” the expert from the Ice Service explains.
Ice is even more likely to be found in the northernmost and easternmost parts of the Baltic –Bothnian Bay and the Gulf of Finland. In the former, the sea ice on the coastline was already up to 65 centimetres thick on 30 January 2026. In the latter, the Ice Service reported fast ice between 20 and 40 centimetres thick on the same date. As such, for the staff of the Ice Service and all Baltic Sea fans, January got the year off to an exciting start (Figures 2 & 3).
Figure 4: Fused pancake ice near Vierow, Greifswald Bodden. Taken on 1 February 2026. Photo: Wiebke Aldenhoff
Figure 5: Optical satellite image of Germany’s Baltic coast near Rügen, 20 January 2026. The northern part of the Greifswald Bodden and sheltered waters near Rügen were covered with ice up to 15 centimetres thick. This can be seen in the ice’s greyish-blue colour, shot through with numerous small white structures. In the southern part of the Greifswald Bodden, new ice – much darker, nearly the colour of the water – was forming. There were a few whiteish structures there, too, though barely visible here. Image: Copernicus Sentinel-2 [contains modified Copernicus Sentinel Data 2026]
Figure 6: Physicist Wiebke Aldenhoff gathers and analyses extensive data on the ice situation in the Baltic for the Federal Maritime and Hydrographic Agency in Rostock, which she uses as the basis for preparing the Baltic Sea Ice Report for shipyards and other interested parties. Photo: private
The Arctic: Too little new sea ice to compensate for past deficits
In the Arctic, January 2026 failed to reverse the trend in sea-ice development: in the Arctic marginal regions of the Pacific and Atlantic alike, there was too little pack ice to compensate for the delayed new-ice formation in the preceding months. There was substantially less sea ice in comparison to the long-term mean in the northern Barents Sea, the region between the Labrador Sea and Davis Strait, the Sea of Okhotsk, and the western part of the Bering Sea. Conversely, satellites detected somewhat more pack ice in the eastern part of the Bering Sea and in Fram Strait (Figures 7 & 9).
The monthly mean sea-ice extent was 13.23 million square kilometres – the fourth-lowest ever recorded in January and, in terms of the statistics for January, coming in slightly behind the low monthly mean values from the years 2025 and 2017 (January 2025 and January 2017: ca. 13.19 million square kilometres, see Figure 8).
In comparison to January 2025, the virtually seamless ice cover on Hudson Bay is a conspicuous difference and indicates that the unusual “ocean heat wave” observed there in the winter of 2024/2025 didn’t repeat itself.
Figure 7: Difference in the mean position of the ice margin in January 2026, compared to the long-term January mean for the years 2003 – 2014. Regions marked in blue had more Arctic sea ice in the first month of the year than in the reference period; those marked in red had less.
Figure 8: Time series of the mean January sea-ice extent in the Arctic. The light blue line represents the long-term trend; the mean for January 2026, at 13.23 million square kilometres, perfectly matched the trendline.
Figure 9: On 14 January 2026, the Arctic waters to the northeast of Svalbard were largely ice-free, as this image from the Copernicus satellite Sentinel-1 shows. Pack ice from the east only entered the area in the fourth week of January. Image: European Union, Copernicus Sentinel-1
Nevertheless, sea surface temperatures were high in the ice-free regions of the Arctic Ocean in January 2026. In the Labrador Sea, temperature sensors recorded a mean anomaly of more than 4 degrees Celsius (Figure 10).
The massive heat surplus is most likely attributable to the unusually high air temperatures in the region (Figure 11) and to the progressive warming of the ocean in response to anthropogenic climate change.
Figure 10: Mean sea-surface temperature anomaly in January 2026 in the Arctic.
Figure 11: Mean air temperature anomaly in January 2026 in the Arctic. The temperature development was characterised by major contrasts: while the air masses over Greenland and adjacent regions were markedly warmer than the long-term mean, temperatures dropped well below the mean over Eastern Europe and Siberia.
Ocean heat absorption reaches a new record high
According to a new study, in 2025 alone the ocean absorbed roughly 23 zettajoules of thermal energy from the atmosphere, which were then stored in the upper 2,000 metres of the water column – the largest heat surplus absorbed by the ocean in a single year since the beginning of record-keeping.
For those of you who have no idea what a zettajoule is, the study’s authors also provide comparisons. In 2025, the ocean absorbed ca. 210 times as much energy as the total global electrical output. Or, put another way: the amount of heat surplus absorbed in 2025 was the equivalent of twelve of the atomic bombs dropped on Hiroshima exploding once per second for every day of the year. In other words: an incomprehensibly large amount of energy.
For the regularly released study on ocean heat content, the participating teams of scientists from eight countries chiefly assess temperature data from what are known as Argo floats. Thousands of these cylindrical monitoring devices drifting in the ocean autonomously measure and record various parameters, especially water temperature and salinity, to a depth of up to 2,000 metres (Figures 12 & 13).
Figure 12: Ocean heat content anomaly in 2025 compared to the mean value for the reference period 1981 – 2010. The numbers in the colour scale are in gigajoules or 109 joules per square metre. Graphic: Pan et al., 2025 (CC BY 4.0).
Figure 13: The German research icebreaker Polarstern in the Antarctic. In the foreground, the antenna of an Argo float can be seen. Photo: Alfred Wegener Institute
The Antarctic: Summer sea-ice melting significantly slowed
In the Antarctic, the summer sea-ice melting slowed significantly in January 2026. The sea-ice extent dropped somewhat less than by half – from ca. 6 million square kilometres on the first day of January to 3.62 million square kilometres on the last. The monthly mean extent was 4.46 million square kilometres, putting January 2026 in 14th place in the time series.
In January, large ice-free areas in Antarctic waters were especially to be found off the coast of Marie Byrd Land, in the Bellingshausen Sea, and off the coast of Wilkes Land. In contrast, there was more pack ice in parts of the Weddell Sea, off the coast of Adélie Land, and in the western Ross Sea. “The real question now is whether the sea-ice melting will accelerate again in February. That’s what we’ve seen in the past two summers,” explains Dr Klaus Grosfeld, a climate expert at the Alfred Wegener Institute and co-initiator of the Sea Ice Portal (Figures 14 & 15).
He and his colleagues are following the current development of sea surface temperatures in the ice-free coastal regions with great interest. “For instance, we’re seeing unusually high surface temperatures off the west coast of the Antarctic Peninsula and in the Ross Sea. Which raises the question of where the heat is coming from. From the atmosphere, or is it up-welling warm water from the depths in these coastal regions?” (Figure 16).
Figure 14: Mean sea-ice concentration in the Antarctic in January 2026. The turquoise line indicates the mean margin of the sea-ice extent for the period 1981 – 2010.
Figure 15: Difference in the mean position of the ice margin in January 2026, compared to the long-term January mean for the years 2003 – 2014. Regions marked in blue had more Antarctic sea ice in the first month of the year than in the reference period; those marked in red had less.
Figure 16: Mean sea-surface temperature anomaly in the Antarctic in January 2026. The unusually high surface temperatures on the west coast of the Antarctic Peninsula and two coastal areas of the Ross Sea can be clearly recognised.
Polarstern expedition investigates sea-ice changes in the northwest Weddell Sea
Increasingly warm surface water, and its effects on the Antarctic sea ice and the organisms living on, in and below it, will also be a focus of the German research icebreaker Polarstern’s next expedition. The expedition, which will begin just days from now, departing from the Chilean port of Punta Arenas, will take an international team of researchers to the northwest Weddell Sea (Figure 17).
The region is one of the least-researched in the world, as its year-round sea-ice cover makes it virtually inaccessible. But since 2017, there have been recurring, substantial declines in the sea-ice extent there – most likely because warmer water finds its way to the surface or the surface water warms for some other reason.
“These changes could be the harbinger of substantial changes in the northwest Weddell Sea that impact the region’s entire physical and biological ice-ocean system, including Larsen C Ice Shelf,” report cruise leaders Prof Christian Haas and Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in the expedition programme.
Currently, there is more and thicker pack ice than expected in the target region. Accordingly, it is questionable whether the research icebreaker will be able to reach Larsen C Ice Shelf. In any case, the experts on board will carry out the range of planned measurements concerning ice thickness, snow properties and water-related parameters, as well as the fauna in the northwest Weddell Sea and its biological carbon cycles.
If you’re interested in following their scientific work, there are a number of ways to do so. In the Polarstern blog, the two cruise leaders regularly share impressions from the day-to-day expedition work. On her project website, AWI sea-ice physicist Prof Stefanie Arndt and oceanographer Dr Sandra Tippenhauer report on their work regarding sea ice, snow, and the water masses and currents below the pack ice. And needless to say, you’ll continue to hear from the Antarctic researchers in our upcoming sea-ice updates (Figure 18).
Figure 17: This map shows the target region for the upcoming Polarstern expedition in the northwest Weddell Sea. Map: AWI
Figure 18: In two separate scientific blogs, cruise leaders Christian Haas and Ilka Peeken (top row) and AWI experts Stefanie Arndt and Sandra Tippenhauer (bottom row) report on the Polarstern expedition to the northwest Weddell Sea. Photos: Alfred Wegener Institute & private
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Wiebke Aldenhoff, BSH Ice Service
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Sina Löschke (Science Writer)
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