The importance of whitecapping to air-sea interaction and Earth observation approaches to its retrieval

A number of geochemical processes are dependent on bubbles primarily produced by “whitecapping” breaking waves, notably primary marine aerosol production, bubble-mediated gas exchange and the renewal of the organically rich surface marine microlayer. It is convenient to predict the magnitude of these processes through a “whitecap method” that then requires whitecap coverage to be measured or predicted. Whitecap coverage is difficult to define and harder to measure. There is adequate evidence that whitecap coverage (and thus by implication, the processes driven by it) do not simply depend on wind speed. Typically whitecap coverage may vary by a factor of two either side of a geometric mean for a given wind speed in response to changes in sea state. Both parametric and relatively direct methods of retrieving whitecap coverage require further development.