Bubble plume depths and surface wave development as a control on ambient sound in the ocean

Wind, wave, and acoustic observations are used to test a scaling for ambient sound levels in the ocean that is based on the relative penetration depth of active bubbles during surface wave breaking. The focus is on acoustic frequencies in the range 1-10 kHz, which are typically scaled by wind speed alone. Wind and wave information are combined in a parametric form to describe the depth of the active bubble layer (which produces sound) relative to the depth of the passive bubble layer (which attenuates sound). The relative depth scaling has a primary dependence on wind speed and a secondary dependence on any departure of significant wave height from fully-developed, open-ocean conditions. The scaling is tested with long time-series observations of winds and waves at Ocean Station Papa (North Pacific Ocean), as well as with a case study with fetch limitation near the island of Jan Mayen (Norwegian Sea). When waves are less developed (e.g., limited by fetch) at a given wind speed, the attenuating layer is relatively thin and the sound levels are higher. The scaling is a plausible explanation for the observed reduction in sound levels during high wind events (winds greater than 15 m/s).