UC San Diego

Human activities introduce high levels of noise into the ocean. Commercial shipping, in particular, has increased to the point that ships make a larger contribution to ocean noise than natural noise sources for most ocean locations and over a broad range of frequencies. Primeval ocean noise levels, those that would have been experienced before the advent of human-made noise in the ocean, are largely unknown. Ocean noise monitoring efforts began post-industrialization, leaving baseline sound levels under which marine organisms evolved unclear. This study modeled primeval (wind-driven) ocean noise levels and modern (ship noise plus wind noise) ocean noise levels in the Santa Barbara Channel off Southern California. The modern noise levels were validated with acoustic measurements from two sites equipped with High-frequency Acoustic Recording Packages. There was good agreement between the modern noise level models when compared to measured levels for high frequencies, and at a site shielded by islands from long range sound propagation. The lower frequency acoustic environment, modeled at 50 Hz, was more degraded than the higher frequency noise levels, modeled at 1000 Hz. This model can be used to identify target regions and times for noise reduction efforts, as well as model future scenarios for noise reduction to identify techniques with the greatest potential for conservation.