The mixing and secondary circulation in the Delaware River plume during a strong (10 m/s) upwelling-favorable wind event in April 2003 have been observed using a dye tracer. The dye, injected into the halocline at the base of the plume, was surveyed for more than a day as it moved 28 km off shore. The secondary circulation within the plume was resolved as the dye patch dispersed. This flow pattern conformed with numerical model results of Fong and Geyer involving an upwelling flow 8.4x10(-5) m/s (similar to7.3 m/day) and a subsequent near surface, offshore flow (similar to0.09 m/s) across the plume. The salting rate of the plume implied a mean vertical diffusivity of similar to2x10(-4) m(2)/s where the gradient Richardson number was approximately 0.6.
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