Long-term monitoring of marine soundscapes: Shipping, biodiversity and weather at a Pacific seafloor observatory

Seafloor observatories enable long-term monitoring of marine soundscapes, modulated by weather, biodiversity and human impacts (e.g. shipping). High-frequency (96-kHz) measurements at the NEPTUNE node of Folger Deep are processed to compare signatures of shipping and natural events over five tidal cycles, spanning several seasons (2009-2011). Independent meteorological data from local surface stations is also used. Sound levels in third-octave frequency bands centred on 63 Hz and 125 Hz are used to monitor shipping, in line with the European Marine Strategy Framework Directive (MSFD). The contribution from the busy shipping lane 40 km away is affected by the complex, shallow bathymetry, whereas local traffic can increase noise levels by up to 30 dB re. 1 μPa, with strong seasonal variation. The relative contributions of the 63 Hz and 125 Hz bands varied contrary to MSFD expectations for deeper areas. Our results match other studies in shallow, coastal environments, showing the importance of depth in interpreting changes. Principal-Component Analyses show that noise from local vessels is the most significant contributor in all seasons, and weather is the second largest, except in summer when biological noise became prevalent. Biodiversity, measured with the broadband Acoustic Complexity Index, showed a strong correlation with weather.