Wind-driven lateral variability in a partially mixed estuary

A circulation study of the upper Neuse River Estuary (NRE) was initiated to characterize the nature of motion in the lateral dimension and to understand the role that this motion may play in the occurrences of warm weather fish kills. Low frequency winddriven variability in across channel bottom salinity was identified and attributed to variability in the synoptic wind band. Diurnal variability in bottom salinity appeared to be driven by diurnal wind variability, presumably associated with the local sea breeze. In both cases the lateral response of the system was driven predominantly by across channel wind forcing and not by Ekman setup associated with along channel winds. Additional variability at near diurnal periods may have been due to baroclinic seiches. A lateral, barotropic seiche with a period of w30 min was also identified. High salinity water was found to be a good marker for low DO water across the estuary. Wind-driven upwelling of low DO/high salinity water and downwelling of high DO/low salinity water was documented and provides a plausible causal mechanism for the death of pelagic fish in the upper NRE.