Floating Offshore Wind (FOW) will soon add significant capacity to the renewable energy sector. However, data gaps remain with respect to potential environmental risks of these installations. Operational noise from FOW will produce continuous underwater noise over decades to come. While noise signatures from fixed-bottom turbines are well understood, there is uncertainty regarding the noise profile and potential impacts of FOW turbines.
Here, two FOW farms were acoustically surveyed, one with semi-submersible (Kincardine) and one with floating spar (Hywind Scotland) systems. Similar to operational noise of fixed turbines, FOW noise emissions were mostly below 200 Hz and exhibited distinct tonal features between 50 and 80 Hz at Kincardine, and 25 and 75 Hz at Hywind Scotland. The sound pressure levels 100 m from the turbines related to drivetrain vibration and were comparable to sound pressure levels from fixed bottom turbines. In addition, temporally intermittent broadband transients, which were thought to be related to the mooring systems, were recorded at both systems.
Harbor porpoise detections were lower at 300–600 m from the turbines compared to 1500–2400 m at both FOW sites. This work highlights cumulative operational noise of large FOW arrays as a potential stressor to the marine environment. Where possible, effective mitigation options should be investigated.