• circulation dynamics;
  • lagoonal estuary;
  • salt balance;
  • salt flux

[1] Albemarle-Pamlico Sound (APS) is a shallow lagoonal estuary connected to the Atlantic Ocean through narrow inlets. The circulation dynamics and salt balance in this estuary are investigated using a numerical model. Although the vertical stratification is weak, the mean flow features a two-layer gravitational circulation with speeds reaching several centimeters per second. Analysis of the momentum budget shows a primary balance among the barotropic pressure gradient as a result of sea level slope, the baroclinic pressure gradient due to horizontal salinity gradients, and stress divergence. The salt budget for APS is determined by the balance between river flow and salt exchange through the inlets. At the inlets, the salt flux resulting from estuarine shear flow is much weaker than that due to tidal pumping and subtidal barotropic transport. Tidal pumping produces a net influx of salt into APS: Strong flood currents push oceanic water into the estuary through a propagating density front, whereas ebb currents advect lighter estuarine water over denser bottom water. The salt flux due to the subtidal barotropic transport across the inlets shows large temporal fluctuations associated with wind events. This transport can be either a source or sink of salt to APS and correlates well with the sea level difference across each inlet. Higher–sea level on the shelf leads to an intrusion of oceanic water into APS whereas higher–sea level inside APS leads to a withdrawal of estuarine water to the shelf.