Published: 10.09.2020 Updated: 11.02.2022
The first offshore wind farm was established outside Denmark as early as 1991. Later, China, Japan, Germany, the United Kingdom and the United States, among others, have developed offshore wind farms. Several facilities are also being planned in the Norwegian part of the North Sea.
The rapid growth of the offshore wind industry makes it necessary to acquire more and better knowledge about the possible effects of ocean-based wind turbines on the marine environment. The Institute of Marine Research (IMR) is active in researching these questions and provides advice for the government and industry on how to avoid negative unintended consequences of offshore wind farms.
If renewable energy from offshore wind turbines replaces fossil energy, it can help reduce greenhouse gas emissions. Man-made climate change affects the marine environment and ecosystem in a number of ways, including through warming, sea level rise, ocean acidification and other ocean currents.
These changes are already underway, but reduced greenhouse gas emissions can reduce the pace and limit the scope.
Offshore wind turbines have so far mostly been installed on fixed foundations in relatively shallow waters. Floating turbines are expected to become more common in the future. Such turbines can be installed further from shore, but they also require anchoring. Foundations and anchors can damage local flora and fauna, including fish species that live and spawn on the seabed. IMR has advised against the development of offshore wind farms in areas that are important for capelin and sandeel, which lay eggs in the sandy bottom.
In the operating phase, wind turbines produce constant, low-frequent noise as long as the rotor blades rotate. This background noise can interfere with communication between marine organisms that use sound for communication, i.e. during spawning. More acoustic measurements are needed to map the level and scope of the noise generated by the turbines as well as how it affects fish and other marine animals.
The cables that carry the current from the wind turbines to land generate electromagnetic fields on the seabed. Many marine organisms, including cartilaginous fish such as skates and sharks, are sensitive to electromagnetic signals. For these animals, electromagnetic signals could potentially interfere with migration and grazing in an area around the cable.
The studies that have been carried out as of today show relatively marginal effects of electromagnetic interference on marine organisms, but more research is needed on this topic.
Wind turbines and anchorages are "fences" in the sea, but they may also function as artificial reefs. Algae and shells can grow on them, and they can attract fish and other animals that seek shelter or food. Especially in open sea areas with sandy seabeds, they can help increase biodiversity. On the other hand, such artificial reefs can also act as stepping-stones for invasive species, allowing them to spread to new areas.
A review of recent research concluded that many fish species are found in larger quantities within wind farms than in the surrounding sea area. It is uncertain whether this is due to an increase in the fish stock, for example due to lower fishing pressure in the area, or whether it is just a distributional effect where the fish are gathering around the wind turbines.
In sum, effects of offshore wind farms on biological productivity and diversity can be positive, negative or neutral. Artificial reef effect and protection against fishing can increase production and lower mortality. Noise, light and electromagnetic can lead to reduced production and higher mortality. The farm can also have neutral or balanced total effects.
IMR publishes an annual report with updated knowledge and advice on seismic and other man-made noise in the sea including offshore wind power. It is probable that the advice will evolve in the coming years as more knowledge is added.
IMR recommends that a standardized protocol be drawn up for offshore wind systems adapted to Norwegian conditions. Such a protocol should include thorough investigations of the area before development, as well as monitoring of both physical and biological changes during operation and after decommissioning of facilities. Collected data should be openly available.
IMR advises against wind farms in important spawning areas or feeding grounds for fish. Development should also be avoided in areas that are particularly vulnerable or valuable to the marine ecosystem.
IMR recommends the use of noise reduction measures such as bubble curtains in the development phase. Development work should not take place during spawning periods for fish or grazing periods for marine mammals in the area. IMR also advises using material that makes the least possible noise when mooring floating turbines.