Frontal observations of the Delaware Coastal Current source region

The Delaware Coastal Current is formed by the outflow of buoyant estuarine water from Delaware Bay. Its source region is concentrated near the Delaware coast at the estuary mouth in a narrow region typically only 4–6 km in width. d a combination of moored current, temperature, and conductivity records together with CTD profiles, underway surface thermosalinograph records, and repeated acoustic Doppler profiling to study the source region hydrographic and current fields with emphasis on its frontal boundaries and their tidal frequency variability. Our central finding is that twin frontal boundaries exist for the source region over much of the tidal period, that is, both its offshore and onshore boundaries are fronts. Between the twin fronts lies the buoyant water of the source region, a conduit for the net seaward transport of buoyancy. frontal boundaries are strongly modulated in horizontal density gradient at theM2 tidal frequency. Maximum gradients occur during early flood current phase. Weaker gradients characterize the ebb current phase. The density gradient modulation is partly explained at both fronts by the occurrence of the lowest salinity and density water in the source region near the time of slack water before flood. Near the offshore front, furthermore, horizontal convergence of the flood tidal currents provides subsequent frontogenesis, so that peak frontal density gradients are reached there during the flood current phase.