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