Photo by Sander Weeteling
Existing offshore wind farms in the North Sea are already redistributing up to 1.5 million tonnes of mud and associated organic carbon each year, according to new research published in the journal Communications Earth & Environment by scientists at the Helmholtz-Zentrum Hereon in Germany. The study, the first to model the combined effects of offshore wind infrastructure on atmosphere, waves, currents and sediment transport simultaneously, warns that these effects will intensify significantly as capacity continues to expand.
Suspended particles are constantly in motion across the North Sea, stirred up from the seabed by waves and currents and supplemented by material carried in from the Atlantic and from rivers. Under natural conditions, this material drifts through repeated cycles of settling and resuspension before accumulating as mud in calmer, low-current areas. The Hereon researchers found that offshore wind turbines disrupt this process in two ways: their rotors slow surface currents over a wide area, while their underwater foundations alter tidal flows. Together, these changes are causing a significant spatial redistribution of sediment across the seabed.
The study finds that wind farms can alter net sediment transport fluxes by up to 30% locally, reducing mud accumulation in established depositional zones while creating new ones elsewhere. Around 52% of the total redistribution is concentrated in the German Bight. Turbines are also retaining approximately 1.5% of the annual riverine sediment input that would otherwise flow from the North Sea into the Atlantic – a change with potential consequences for nearshore systems, including the Wadden Sea, which depends on a continuous sediment supply to keep pace with rising sea levels.
Carbon burial implications
The findings carry implications beyond sediment dynamics. Seabed sediments act as a significant long-term carbon store: as dead marine organisms sink and accumulate with mud particles, the organic carbon they contain can be locked away for centuries. The study estimates that wind farms are already redistributing around 0.07 million tonnes of particulate organic carbon annually alongside the sediment – altering where and how effectively this carbon is buried.
Lead author Jiayue Chen, from the Hereon Institute of Coastal Systems – Analysis and Modelling, said: “Our simulations suggest that these amounts will accumulate increasingly over the coming decades as offshore wind farms expand. This could affect the long-term functioning of the ecosystem and carbon storage in the North Sea.” Noting the concentration of effects in the German Bight, Chen added that this “highlights this region as particularly affected.”
The team’s next priority is to investigate how these changes affect sensitive coastal areas, with the Wadden Sea — a UNESCO World Heritage Site and one of Europe’s most important intertidal ecosystems — identified for further study, alongside a broader examination of how sediment shifts are influencing the ocean’s role as a carbon sink. Chen said: “With an improved understanding of sediment distribution and carbon storage in the North Sea, we can assess long-term risks to coastal stability, navigational safety in shipping, and the functioning of ecosystems in the German Bight. Our findings provide a valuable foundation for the sustainable expansion of offshore wind energy and help decision-makers in politics, business, and industry to plan new wind farms in an environmentally friendly way.”
A rapidly expanding footprint
The findings arrive at a moment of major policy significance. The EU aims to increase North Sea offshore wind capacity more than tenfold by 2050. A companion study by Hereon researchers, published in the same journal in February, foundthat large-scale wind development could reduce current velocities across the North Sea by up to 20% and cause long-term sea surface warming of up to 0.2°C in wind farm areas – effects that would compound the sediment and ecosystem changes identified in the new research.
Dr Nils Christiansen, who led the hydrodynamics study, said: “Offshore wind power is a key component of the energy transition and decarbonisation. At the same time, we need to understand how different types of offshore installations and the size of the turbines affect the North Sea. Only then can we provide society and the economy with sound information and develop measures to minimize potential risks at an early stage.”