Numerical study of the diapycnal flow through a tidal front with passive tracers

A two-dimensional numerical model is used to study the diapycnal flow through a tidal front with passive tracers. In a basic numerical experiment a passive tracer is released into the bottom water at the offshore edge of a tidal front, and it subsequently moves on-bank with a velocity that decreases with time. This qualitatively agrees with a recent field experiment using a dye tracer on Georges Bank. Additional experiments are performed to investigate the sensitivity of the tracer dispersion to the tidal phase and the location of tracer release within the front. As the release point is moved on-bank across the front, the tracer velocity decreases until it weakly reverses on the on-bank edge of the front. This trend can be understood by considering the structure of the Lagrangian velocity field in the tidal front, the degree of vertical mixing of the tracer, and the concentration-weighted mean patch velocity. The tidal phase at the time of tracer release does not significantly affect the tracer dispersion.