The bottom boundary layer structure in the vicinity of the Middle Atlantic Bight shelfbreak front

Abstract

The velocity structure in the bottom boundary layer (BBL) in the Middle Atlantic Bight (MAB) is investigated using data derived from the Shelf Edge Exchange Processes (SEEP-II) experiment to test theoretical predictions of the effects of cross-shelf buoyancy flux on the BBL which are thought to contribute to frontogenesis at the shelfbreak. The cross-shelf flow is bottom intensified with a direction veering consistent with that of a frictional boundary layer with rotation. The BBL thickness based on veering angle ranges from 8 to 40 m with a velocity dependence complicated by stratification that is dependent on frontal position. There is evidence of the asymmetry in the BBL thickness expected for the cross-shelf buoyancy flux during up- and downwelling events. However, the velocity structure does not define a sharp upper boundary to the BBL as given by simple one-dimensional model calculations and suggests that there must be other sources of turbulence in addition to bottom friction.