Reduced upper ocean turbulence and changes to bubble size distributions during large downward heat flux events

Abstract

During the Radiance in a Dynamic Ocean (RaDyO) field study south of Hawaii in September 2009, simultaneous observations of total heat flux, upper ocean turbulence, and bubble size distributions suggest that large downward heat flux modulates the upper ocean turbulence dissipation rates and subsequently the upper ocean bubble field. The observations show that the turbulence dissipation rates near the ocean surface are reduced by a factor of 10 during periods with high downward heat flux (>400 W m−2). Simultaneously, the observations of bubble size distributions at a depth of 0.5 m show that there were significantly lower concentrations of bubbles with radii >100 μm than during a winter study in the Gulf of Mexico. Also, the number of bubbles with radii >200 μm is found to be dependent on the heat flux, with fewer such bubbles during stable (positive heat flux) conditions. The reduced number of larger bubbles reduces the effect of the bubble field on optical reflectance by up to a factor of 3 compared to other locations at similar wind speeds.