Acoustic twilight: A year-long seafloor monitoring unveils phenological patterns in the abyssal soundscape

Despite the perpetual darkness of the deep sea, contrasting the sunlit epipelagic waters, many deep-sea organisms exhibit rhythmic activities. To discern environmental cues that may serve as entrainment signals for deep-sea organisms, this study investigated the soundscape of the abyssal plain south of Minamitorishima Island. Our analysis revealed clear diel and seasonal patterns, primarily driven by evening fish choruses and marine mammal vocalizations. These evening choruses, discernible above the background noise, likely serve as a circadian time cue for organisms capable of perceiving them within the aphotic depths. In addition, the frequent detection of whistles and echolocation clicks suggests this region functions as a foraging ground for marine mammals. These acoustic cues might guide organisms with auditory capabilities toward habitats rich in sinking food debris and whale falls. By elucidating the ecological processes shaping abyssal soundscape dynamics, these findings open new directions for further exploration in deep-sea chronobiology.