The 10th Ocean State Report, published on the 30.09.26, provides both a comprehensive snapshot of the changing ocean and the challenges ahead and enables informed decisions to strengthen resilience. One of the key takeaways of the report is a direct outcome of research conducted by the Nansen Center.
Produced by Mercator Ocean International for the Copernicus Marine Service, this year’s report brings together contributions from 125 scientists from Europe and around the world. It documents how the ocean has been changing and what those changes mean for ecosystems, coastal communities, and economies.
Drawing on long-term records from satellites, in-situ observations, and output from numerical models, the report helps scientists, policymakers, and the wider public understand what is happening in the ocean, where changes are occurring, and why they matter.
The report is divided into two main sections. The first focuses on “Ocean Knowledge”, documenting extreme events, long-term trends, and their impacts. The second, “In Action”, highlights how ocean knowledge and data are great tools to support adaptation, resilience, and decision-making.
Key takeaways: Extreme events
- The Mediterranean and Black Seas experienced marine heatwaves that broke records in both intensity and duration in 2024: Some lasted over a month, with temperatures more than 4.6 degrees above average.
- In the same year, an intense storm led to a record-breaking low in sea-level: In the Bothnian Bay, it dropped temporarily by 1.53 m. Thanks to effective warning systems, the necessary preparations could be made several days before the event. Countries around the Bothnian Bay were able to plan for a temporary suspension of ferry services lasting nearly a full day.
Key takeaways: Long-term trends
- Small island states are directly impacted by overlapping pressures due to climate change, such as for example sea-level rise, rapid ocean warming, and an increasing risk for tropical cyclones.
- Seasonal changes of phytoplankton in about 5% of the global ocean have shifted persistently during the three past decades, pointing to an ongoing reorganisation of marine ecosystems around the world.
- For multiple decades, the Barents Sea has been experiencing an increase in salinity (called “Atlantification”). During 2016-2022, this process temporarily paused. Instead, the Barents Sea experienced an unprecedented reduction in salinity.
This last key takeaway from the report is an outcome of collaboration between the Nansen Center, the Institute for Marine Research, and three institutions in India.
The relatively shallow Barents Sea, a main gateway to the Arctic, is a key region where Atlantic water cools and becomes heavier. This heavy water sinks and contributes to the formation of intermediate and deep waters in the Nordic Seas, ultimately feeding the lower limb of the Atlantic Meridional Overturning Circulation (AMOC), an important component of the so-called global thermohaline circulation. Driven by differences in temperature and salinity, this circulation redistributes heat around the globe and plays a major role in shaping regional and global climate.
The team around Roshin P. Raj set out to study the drivers of the interannual variability and recent changes in the seawater flowing in and out of the Barents Sea between 1991-2024. The most striking event during this period was a remarkable decrease in salinity in the entire Barents Sea between 2016-2022, described as a “freshening” of the seawater in the region. They found that this drop in salinity had multiple contributors: In the southern Barents Sea, freshening was mainly caused by a decline in the salinity of Atlantic water entering the region. Further north, the trend was driven by two factors; the inflow of less saline Atlantic water, and an increase in sea ice import from the Arctic. When the sea ice melted, it released freshwater into the ocean, contributing further to the decrease in salinity.
During this unprecedented decrease in salinity in the Barents Sea between 2016-2022, Raj and his colleagues found that the dense water exiting the region were lighter than normally, which can potentially impact the dense waters feeding the lower limb of the Atlantic Meridional Overturning Circulation (AMOC).
This trend of temporarily decreasing salinity is part of the broader changes scientists are observing across the Arctic Ocean and surrounding seas, where shifts in salinity can influence ocean circulation, sea ice, and marine ecosystems.
This study shows that the careful combination of satellite, in-situ, and modelling data provides yet another piece of the puzzle to understanding changes in our oceans. The freshening of the Barents Sea is just one example of the changes documented across the global ocean in this year’s Ocean State Report. Together, these observations help build a clearer picture of how the ocean is responding to climate change, and why long-term monitoring remains essential for understanding what comes next.
Key researchers: Roshin P. Raj, Antonio Bonaduce, Laurent Bertino
