SUBTIDAL FREQUENCY ESTUARY-SHELF INTERACTION - OBSERVATIONS NEAR DELAWARE BAY

Interaction between a large estuary and the adjacent inner continental shelf at subtidal frequencies occurs through a variety of physical processes. I use recent field observations to study these processes near the weakly stratified estuary of Delaware Bay on the east coast of the United States. The primary observations were shipboard hydrography and long time series of current, temperature, and conductivity. The observations revealed three distinct spatial regions for the coupled circulation between estuary and shelf: the estuary mouth, the inner shelf where the mean flow is landward, and a buoyancy-driven coastal current. The coastal current is the principal discovery of the work. It begins near the estuary mouth as lighter water from Delaware Bay exists the mouth on the right side when viewed to seaward. Initially, the current is about one internal Rossby radius in width, but it broadens as it flows seaward to reach a width of about 20 km off the coast Delaware. Observed mean currents were 3-5 cm s-1 there. In all three regions temporal variability in current and salinity was induced by variations in alongshore wind and river discharge into the estuary, the latter occurring mainly at very long periods of several weeks and longer.