Offshore windfarms face several obstacles, but one less considered is mines from the Second World War.

Located 85km north of the island of Borkum in the German North Sea, Nordlicht I with a capacity of around 980 MW and Nordlicht II with around 630 MW are expected to be operational in 2028.

However, wartime remnants still lie dormant on the seabed and pose a real danger to people, technology and the environment.

Over the past two years, large-scale geophysical surveys of the seabed identified magnetic anomalies in the area of Nordlicht I and II, indicating the presence of metal objects. The anomalies were interpreted by experts as possible unexploded ordnance, or UXO.

During spring this year, each of the objects was examined and identified individually using a Remotely Operated Vehicle, ROV. As a result, three sea mines were discovered, each with an explosive charge equivalent to 200–300 kg of TNT.

“Clearing the seabed of wartime ordnance is one of those invisible but vital steps in developing offshore wind,” says Tobias Kulgemeyer, senior UXO engineer at Vattenfall Business Area Wind and technical lead for the campaign.

A special aspect of this kind of underwater operation is the use of a 90-meter-long bubble curtain vessel. The vessel lays out a double hose ring on the seabed that generates a curtain of air bubbles to dampen the sound around the detonation site, protecting marine life from noise and stress.

With the seabed now safely cleared, the Nordlicht project is well-positioned to begin installation activities.

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