Observations of Langmuir circulation in the open ocean using acoustic instrumentation mounted on a subsurface drifting package

Abstract

The air-sea interface of the ocean is an energetic and dynamic environment that poses challenges for the positioning of instrumentation. One way to avoid the complexities of placing instrumentation at the ocean surface is to position a platform at some distance below the surface and sample surface processes remotely using acoustic systems. David Farmer recognized the value of such a sampling approach and led the Ocean Acoustics group at the Institute of Ocean Sciences to develop the required capabilities in the late 1980s. We report on observations made during a cruise to Ocean Station Papa in October 1987. Acoustic instruments revealed persistent bands of subsurface bubble clouds spaced by 5 to 10 m and extending in length up to 100 m. The clouds were aligned with the prevailing wind direction consistent with the organization expected from Langmuir circulation. Average downward velocities of 6 cm/s were observed in the bubble plumes that extended to a depth of 15 m. These early observations of near-surface processes motivated a series of instrumentation developments that have helped to explore the richness and complexity of movements within the ocean mixed layer.