Exchange through a back-barrier estuary inlet with complex bathymetry

Shallow, well-mixed estuarine systems behind barrier islands differ from the more commonly studied partially-mixed estuaries in their salinity structure and connectivity with the coastal ocean. Little Egg Inlet links the back-barrier estuaries along the coast of New Jersey, USA, to the inner shelf. It is a largely unmodified inlet with dynamically migrating barrier shorelines and sandbars. Shipboard surveys of the inlet were conducted in 2018 and 2019 with conductivity-temperature-depth and acoustic Doppler current profilers to characterize velocity and density over the tidal cycle under spring and neap tide conditions. Surveys on three separate days revealed residual volume transport directed into the estuary, in agreement with prior observation and modeling results. This inflow partitions approximately equally into two sub-estuaries to the north and south of the inlet. Scaling analysis indicates that the observed laterally sheared flow is influenced by frictional effects over sand bars and shoals as well as centrifugal acceleration around channel curvature. Over the semidiurnal tidal cycle, the inlet undergoes weak to moderate periodic stratification and tidal trapping of distinct water masses from the northern and southern branches. We discuss the role of tidal forcing, bathymetry and salinity gradients in intra-estuary and estuary-shelf exchange. These physical conditions have implications for sediment redistribution and larval dispersal in this and similar barrier inlet systems.