Small-scale transfer processes between the ocean and atmosphere are central to determining weather and climate. During moderate to strong wind speeds the wind-driven ocean wave field entrains large numbers of bubbles thought to be important for a number of transfer mechanisms, including bubble-mediated CO2 transport and the production and biological enrichment of marine aerosols. Despite the importance of bubble-mediated processes very little open ocean data exists on bubble creation rates and the present time there is no reliable method for obtaining these data in the field. This project explores the idea of using the underwater ambient noise to estimate bubble entrainment rates at the air-sea interface by breaking wind waves. The immediate goal of the proposed experiments is to transition an existing wave noise model developed for single plunging laboratory breakers to wind-driven spilling breakers. The primary questions are: 1) Can the existing wave noise model accurately reproduce the noise from individual spilling breakers over a variety of energetic scales? 2) Can the noise from an ensemble of simultaneous spilling breakers be reproduced? 3) Can bubble creation rates, inferred from breaking wave noise, be reconciled with independent estimates of bubble creation rates made during the course of the experiment?
These questions will be addressed with a series of laboratory studies with spilling breakers in a wind-wave channel. The noise of individual spilling breakers within a defined study volume will be monitored with hydrophone arrays and video cameras, and correlated with physical measurements of the wave and entrained bubble plumes. The primary plume characterization will be bubble size distributions measured with an array of fiber optic probes. Measurements will also be made of the noise field from simultaneous multiple spilling breakers. Tank reverberation will modify the measured wave noise and will be compensated for using a method successfully applied to earlier wave channel measurements. Wave noise measurements will be compared with model calculations of wave noise based on the measured physical properties of individual spilling breakers.
Broader Impact. The experiment and data analysis will include the participation of undergraduate interns from UCSD and the SIO summer research fellowship program. These programs sponsor students from around the country to gain hands-on experience in oceanography. A post-doctoral scholar will be employed to manage the primary experiment. The results of the proposed research are likely have broad impact in the field of air-sea exchange processes during moderate to strong wind speeds, particularly those associated with air sea gas transfer of CO2 and marine aerosol production. These processes are ultimately tied to climate dynamics.
