Large-scale wind farms can strongly influence marine primary production as well as oxygen levels inside and outside wind farm areas.
These are the findings of scientists from the Helmholtz-Zentrum Hereon, a North Sea research institute, published in the journal Communications Earth & Environment.
Different wind conditions and currents, more precipitation and a changing surface climate: the effects of offshore wind farms in the North Sea are diverse and have not yet been fully investigated. Some of them are already occurring, others are still to be expected due to the constant expansion of wind turbines in large-scale wind farms. To better understand them and fill the remaining knowledge gaps, a team of researchers at the Hereon Institute for Modeling and Analysis of Coastal Systems is working on different key elements of the problem.
For example, Nils Christiansen's team showed that turbulent wakes (air vortices caused by wind turbines) change the flow and stratification of the water beneath them. But the climate just above the sea surface is also changing permanently, as another team led by Dr. Naveed Akhtar was able to demonstrate.
The latest study, led by Dr. Ute Daewel, now confirms that these impacts also lead to an altered spatial distribution of marine ecosystem components. This includes the distribution of nutrients, phyto- and zooplankton, as well as biomass in the sediment, the food base of many bottom-dwelling organisms.
In the model study, the team assumed large-scale offshore wind farms planned in the North Sea. For deeper marine areas, the researchers found that the amount of biogenic carbon in the sediment would increase locally by 10% and the oxygen concentration, in an area where it is already very low, could decrease further.
In addition, the wind shifts already tested would lead to a local modification of the primary phytoplankton production by up to +/- 10%. And this not only in the wind farm areas themselves, but also distributed throughout the southern North Sea. This means that even if the total production in the region changes very little, there is a spatial redistribution of production. This also has consequences for the distribution of zooplankton, the food base of many fish species. The early life stages of fish in particular often depend on the availability of zooplankton "at the right time in the right place".
A spatial and temporal restructuring of zooplankton distribution can influence these process chains and thus positively or negatively affect the amount of fish available. Therefore, the small change in primary production would have a lasting impact on the entire food web in the southern North Sea.
"Our results show that the large expansion of offshore wind farms will have a significant impact on the structuring of coastal marine ecosystems. We need to better understand these impacts quickly and also take them into account in the management of coastal ecosystems," concludes Ute Daewel in a statement.