Infrasonic acoustic energy produced by offshore wind turbine energy generation may interfere with bird and cetacean navigation cues.

Offshore wind turbine farms are being planned and installed throughout the coastal areas of the global ocean. Noise concerns from these activities are typically framed within frequency bands of concern defined by governmental regulatory agencies (NMFS - OPR, 2018). A less considered noise source are the various infrasonic noises generated by large rotating blades in a pressure-dynamic medium. These noises include the infrasonic "thumps" generated by the motion of the turbine blades as they intersect the "stagnate wind area" on the windward side of the mast (Clancy 1975). A second source of infrasonic energy is the collapse of tip vortices generated by the sudden air pressure gradient transitions across the turbine blades (Vermeer et al. Prog Aerospace Sci 39:467-510, 2003), and the associated "Blade-Vortex Interaction" (BVI) (Brentner and Farasat Prog Aerospace Sci 39(2-3), 2003). These infrasonic sources contain a lot of energy (Edwards 2015) and are in the perceptual range of migratory birds and baleen whales. Given that birds, and potentially whales use infrasonic sound and barometric pressure signals for navigation and migration cues, the installation of thousands of turbines globally may impose significant impacts on migratory birds along avian coastal migratory routes. Additionally, increasing anthropogenic infrasonic noise throughout the ocean may impact and compromise mysticete communication channels and potentially low frequency navigation cues used by these animals.