Here are the main ways warm-water anomalies/marine heatwaves are affecting the waters off Norway, including ecological, commercial, and climate-related impacts.
1. Salinity and Water Mass Changes / Atlantification
In Isfjorden (in Svalbard), warmer Atlantic water has been intruding into deeper layers (below ~100 m), displacing colder, fresher Arctic water, a process known as Atlantification.
The overall salinity around Svalbard and in Barents Sea fjords has been declining since about 2018, partly due to inputs of fresh water from melting glaciers, snow, sea ice, precipitation. This dilutes the water but warmer water masses are still arriving.
2. Marine Heatwaves & Raised Sea Surface Temperatures
There have been episodes of ocean temperatures 5C+ above normal in regions off the Norwegian coast (e.g. Trøndelag to southern Norway), which is unusually large deviation.
In northern Norway during summer 2024, there was one of the worst marine heatwaves on record: temperatures exceeded ~18C—over 4C above long-term average.
3. Aquaculture / Fisheries
Salmon lice outbreaks: The 2024 heatwave contributed to a record salmon lice outbreak in aquaculture sites, causing higher mortality in farmed salmon and economic losses.
Changing distribution of fish species: Warmer conditions are allowing more warm-water species to move northward; some cold-adapted species may decline in their traditional ranges.
Risk to farmed species: Cod farming is particularly under threat, since cod require cooler waters. Warmer sea temperatures complicate aquaculture planning and operations.
4. Ecosystem and Biodiversity Effects
Zooplankton and Phytoplankton changes: The composition of plankton communities is shifting. For example, Calanus finmarchicus, an important cold‐water copepod species, is being outcompeted in some areas by more warm-water relative species. That has knock-on effects up the food chain (fish larvae etc.).
Ancient / cold-adapted microfauna: Species that are adapted to colder and more stable temperatures (such as certain radiolarians) are declining in warmer fjords (e.g. Sognefjord), indicating sensitivity to these changes.
Marine mammals & seabirds: Loss of ice cover and warmer water change habitats for species like whales, seals, etc. Their feeding grounds may shift; behaviors or migration patterns may be disrupted.
5. Chemical/Physical Ocean Changes
Ocean acidification: Warmer waters make the ocean absorb CO₂ differently, lowering pH and affecting calcifying organisms like corals, molluscs, etc. In Norwegian and Nordic seas, acidification trends are faster than global averages in many measured places.
Stratification / nutrient mixing: Warmer surface water plus increased freshwater makes layers in the water more stratified (less mixing). This reduces the vertical transport of nutrients from deep waters to surface, which can limit phytoplankton growth.
6. Socio-economic Impacts
Fisheries: Shifting fish stocks means fishing industries must adapt. Some fish that were abundant become less so; others may become more common but may not have as high commercial value or may require infrastructure changes.
Aquaculture: Higher disease / parasite pressure, more stress for farmed fish, mortality, increased costs. As noted with the salmon lice outbreak.
Uncertainty for management: Because many species are moving, and conditions becoming more variable, it’s harder for fisheries quotas, conservation, aquaculture siting etc, to plan.