On the clouds of bubbles formed by breaking wind-waves in deep water, and their role in air-sea gas transfer

Abstract

Clouds of small bubbles generated by wind waves breaking and producing whitecaps in deep water have been observed below the surface by using an inverted echo sounder. The bubbles are diffused down to several metres below the surface by turbulence against their natural tendency to rise. Measurements have been made at two sites, one in fresh water at Loch Ness and the other in the sea near O ban, northwest Scotland. Sonagraph records show bubble clouds of two distinct types, ‘ columnar clouds’ which appear in unstable or convective conditions w hen the air temperature is less than the surface water temperature, and ‘ billow clouds ’ which appear in stable conditions w hen the air temperature exceeds that of the water. Clouds penetrate deeper as the wind speed increases, and deeper in convective conditions than in stable conditions at the same wind speed. The response to a change in w ind speed occurs in a period of only a few minutes.