Azipod-equipped vessels in the Antarctic Peninsula radiate underwater continuous mid-frequency narrowband and tonal sounds.

Abstract

It is commonly accepted that ocean noise from marine traffic is mostly confined to low frequencies. This article empirically demonstrates that large (length >120 m) vessels equipped with electrically driven "Azipod" propulsion systems generate loud mid-frequency (3-15 kHz) tonal and mid-frequency narrowband and tonal sounds (MF-NTS). The study focuses on six Azipod-equipped tourist vessels operating in the Antarctic Peninsula; it relies on opportunistic passive acoustic measurements collected there during the 2024-2025 Austral summer. The six vessels considered here all radiate MF-NTS, which are interpreted as the acoustic signature of the Azipod (data below 2 kHz are not considered in this study). This signature dominates the ambient sound for several kilometers around the vessel, and can be acoustically detected at ranges exceeding 5 km.