Bubble plume structure: a synthesis of the data from the HiWINGS cruise and comparison with past measurements

The bubbles underneath breaking waves in the open ocean are thought to make a significant contribution to air-sea gas flux and aerosol production, but little is known about the details of bubble plume structures and the small-scale physics controlling them. During the HiWINGS cruise in October and November 2013, we deployed a large spar buoy carrying a range of instruments for measuring subsurface bubbles. Combining acoustical techniques (upward-looking sonar and resonators), optical techniques (custom-built bubble camera and whitecap camera) and auxiliary measurements has given us a unique data set, since it enabled us to follow individual bubble plumes over a range of length and timescales. The buoy floated freely in storms (with wind speeds up to 35 m/s), and data was acquired simultaneously on all instruments. The sonar data covers the entirety of each bubble plume, and we have detailed bubble size distribution measurements from known positions inside the observed plumes, along with photographic data of the associated whitecap.

We will discuss the small-scale details of the bubble plumes observed, and the physical processes that may be responsible for the observed bubble behaviour. . The possible effect of surfactants, water temperature, wind speed and wave state will be examined. Comparisons with past data sets will provide context, and our aim is to relate the different types of bubble measurements within a single framework, in order to understand the overall behaviour of the bubble plumes. In addition, preliminary data relating the observed foam patches to the details of the bubble plumes underneath will be presented.