Langmuir supercells on the middle shelf of the South Atlantic Bight: 1. Cell structure

Langmuir circulation cells extending through entire water columns exert a profound influence on sediment transport on shallow shelves, hence their designation as "Langmuir Supercells" (LSs) upon discovery in 2004 in water of 15 m depth at the Long-Term Ecosystem Observatory (LEO) off New Jersey (United States). Until now, similar high-frequency, full water column measurements of turbulent velocities and density fields have not been reported from significantly deeper continental shelf environments. Such deeper measurements are needed to determine whether LSs exist to influence sediment transport outside the inner shelf. In this article, that deficiency is addressed, using measurements from a midshelf location in the South Atlantic Bight. These data indicate that LSs form during high wind and wave forcing in water of 26 m depth and are thus capable of affecting sediment transport over more than about half of the area of this wide, shallow shelf. Relative to those at LEO, the LSs reported here are less organized and more temporally variable despite similar magnitude forcing. Possible causes of cell weakness and variability are considered.