Ambient sound characterization over decadal time scales in the Atlantic Ocean

Gaining more knowledge about the variations in the ambient ocean soundscape plays a critical role in assessing the human impact (anthropogenic noise pollution) on marine species’ behavior and habitat choices. Accessing historical recordings is important to understand the long-term changes in the ambient sound and to identify mechanistic drivers influencing the soundscape regionally and globally. Data recorded in the Northwest Indian Ocean (Bearing Stake exercise) in 1977 were compared with more recent (2003 and 2013) data from the north side of Diego Garcia Island. This comparison between datasets 40 years apart showed that the ambient sound levels in that region were not higher in the 2000s than they were in 1977. The spectral levels decreased between 1977 and 2003 and then leveled out between 2003 and 2013. These findings are different from the well-cited 3 dB/decade increase in Pacific Ocean sound levels, but they did align with recent studies that also show declines in sound levels in other regions. Therefore, another comparison between acoustic recordings 40 years apart near Bermuda and from an ADEON site (October 1980 and 2018–2020, respectively) was performed to facilitate a better interpretation of how the soundscape is changing over decadal timescales in the Atlantic Ocean.