Icelandic Winter Research Survey Records Unprecedented Ocean Temperatures
Ocean temperatures around Iceland during winter have reached their highest recorded levels since systematic monitoring began in 1970, according to findings from the latest marine research survey.
The annual winter expedition, conducted aboard the research vessel Þórunn Þórðardóttir, concluded on 17 February after 15 days at sea. The survey forms part of Iceland’s long-running environmental monitoring programme, which has tracked seasonal ocean conditions three to four times annually for more than five decades.
Scientists say the long-term monitoring programme is essential for understanding seasonal variability, year-to-year fluctuations and climate-driven changes in the marine environment and its ecosystems.
During the expedition, researchers conducted measurements along ten transects extending from the Icelandic coast into offshore waters. Vertical temperature and salinity profiles were recorded at each station, with a total of 100 monitoring stations sampled during the survey.
Samples were collected at various depths to analyse nutrients, inorganic carbon, which provides insights into ocean acidity, and dissolved oxygen levels. Using a newly installed current profiler, scientists also measured current speed and direction down to depths of 1,000 metres along the vessel’s track, while simultaneously recording temperature, salinity and partial pressure of carbon dioxide.
Additional measurements were carried out in several fjords and coastal areas as part of monitoring environmental impacts from sea-cage aquaculture and to collect data used in assessing the status of coastal water bodies under Iceland’s water management framework. These observations also contribute to the LIFE Icewater research project.
Atlantic Waters Show Record Warmth and High Salinity
The survey found that temperatures in the upper 200 metres of the ocean were generally above the long-term average across most monitoring locations.
At several stations, the recorded temperatures exceeded any previous values measured during winter surveys since the monitoring programme began in 1970.
In Atlantic waters south and west of Iceland, researchers recorded a new winter temperature record of 8.55°C at the Selvogsbanki 5 monitoring station.
Salinity and temperature measurements near Stokksnes also approached record levels, with readings of 35.28 and 8.8°C respectively.
North of Iceland, where Atlantic waters mix with colder polar and Arctic-origin waters, temperatures also reached record values. At station SI4 on the Siglunes section, temperatures climbed to 5.0°C, the highest recorded at that location during winter monitoring.
Scientists also observed that Atlantic water extended further east than usual, reaching as far as Langanes as a subsurface warm water tongue beneath colder surface layers.
However, researchers cautioned that the salinity measurements have not yet undergone final verification, meaning some of the results remain provisional.
Cold Surface Waters Persist in Greenland Sea Stations
Not all areas showed warming trends.
At outer monitoring stations in the Greenland Sea, including LB8 and KG6, salinity levels in the surface layer were lower than those recorded in previous winter surveys. Temperatures there were also unusually low.
These stations typically lie within the East Greenland Current, where polar waters dominate the surface circulation.
Long-Term Warming Trend Continues
Despite significant year-to-year variability, scientists say the broader trend since 1970 shows steadily increasing ocean temperatures around Iceland.
The elevated temperatures south of Iceland suggest that Atlantic water masses may be recovering strength following a period of reduced temperature and salinity that reached its lowest point around 2017.
Researchers say the positive anomalies currently observed, extending deep through the water column, indicate stronger large-scale northward heat transport in the North Atlantic.
Such changes could have implications for regional weather patterns. Iceland recorded its warmest annual air temperature on record in 2025.
Uncertainty Remains Over North Atlantic Circulation
Scientists say it remains unclear how these warm periods may influence deep water formation in the North Atlantic or whether the increased northward heat transport will continue in coming years.
Changes in heat transport can signal either strengthening or weakening of the Atlantic Meridional Overturning Circulation, commonly referred to as AMOC.
The AMOC is a major system of ocean currents that redistributes heat across the Atlantic basin and plays a key role in regulating climate in Europe and the North Atlantic region.
However, researchers caution that determining the current state of this circulation system is difficult using short-term observations alone.
Further long-term research will be required to understand whether the latest measurements represent temporary variability or part of a more sustained shift in North Atlantic ocean dynamics.
Surface temperature and salinity along the ship’s route in February 2026. The stations from which data is shown in the figures below are marked. Image: Iceland IMR
