Baseline Assessment of Underwater Ambient Sound in the Northern Adriatic Sea

Baseline information on underwater ambient sound levels is poorly available for the Mediterranean Sea. The SOUNDSCAPE project filled this knowledge gap, developing a basin-scale, cross-national acoustic monitoring in the Northern Adriatic Sea. Data were collected from March 2020 to June 2021, including the full lockdown period related to the COVID-19 pandemic, at nine stations covering different natural conditions and anthropogenic pressures. Soundscape was monitored continuously 24 h a day by using calibrated stationary recorders (44.1 kHz sampling rate, 16-bit resolution). The entire dataset was analyzed to 20-second averaged sound pressure levels (SPLs) in all the one-third octave frequency bands (base 10). Noise levels for the 63 Hz and 125 Hz one-third octave bans were described, in compliance with the descriptor 11.2 of the EU-Marine Strategy Framework Directive. A difference of about 30–33 dB was found in these frequencies between the quietest and the noisiest monitoring stations, indicating a high spatial variability. Higher SPL median levels were observed where shipping activity was dominant. The SOUNDSCAPE dataset establishes baseline levels for the assessment of future trends in the Northern Adriatic Sea.