Acoustic mapping of Langmuir circulation across a coastal front

An experimental, acoustical study of the interplay between Langmuir turbulence, surface waves, and fronts in a Norwegian fjord was performed. A multi-beam echo sounder was mounted on the top of an autonomous underwater vehicle, and subsurface air bubbles were used as acoustic tracers. The scanned area was 1500 m along track and 300 m across track. The study found that through the trial area, there was a front with pronounced down-welling currents, down to a depth of 10 m, where Langmuir windrows formed on one side of the front, but not on the other. Based on the orientation in the fjord, the findings suggest that the bubble front coincides with a salinity front. If that is the case, it indicates that stratification prevents formation of Langmuir windrows. This article also argues that the Langmuir turbulence is augmented by the presence of swells.