Lagrangian flow at the foot of a shelfbreak front using a dye tracer injected into the bottom boundary layer

Convergent flow at the foot of the shelfbreak front in the Middle Atlantic Eight has been detected using a dye tracer, Rhodamine-WT, injected into the bottom boundary layer. The observations substantiate model simulations by Chapman and Lentz (1994) of convergent flow in the vicinity of the front which would be very difficult if not impossible to detect with conventional moored current measurements. By following the dispersal of the dye patch over a 4 day period Lagrangian velocities of the order of 0.015 mis with respect to the front were resolved even as the frontal boundary was displaced similar to 12 km onshore. The water-following properties of the dye tracer provides a useful technique for studying the small-scale circulation and mixing at the frontal boundary.