An observational study of salt fluxes in Delaware Bay

An observational study was conducted in Delaware Bay during the summer of 2011 aiming to quantify the different mechanisms driving the salt flux in this system. Seven moorings, equipped with bottom-mounted ADCPs and CT sensors at difference depths, were deployed across a section of the estuary. The total area-averaged and tidal-averaged salt flux was decomposed in three different contributions: the advective salt flux that represents the flux caused by river input and meteorological-induced flows, the steady shear dispersion that is the salt flux driven by the estuarine exchange flow, and the tidal oscillatory salt flux that is induced by the tidal currents. The advective salt flux dominated over the steady shear dispersion and tidal oscillatory salt flux, because it was driven mainly by changes in sea surface height associated with wind-driven setup and setdown. The steady shear dispersion was always positive and presented a spring/neap variability that was consistent with a two-layer exchange flow. On the other hand, the tidal oscillatory salt flux fluctuated between positive and negative values, but increased around a strong neap tide and decreased on the following spring tide. This variability is contrary to previous parameterizations, whereby the tidal salt flux is proportional to the amplitude of the tidal currents. The observational estimate was compared to a parameterization that relates tidal salt flux as proportional to tidal current amplitude and stratification. The observational estimate agreed with this new parameterization when the river discharge was relatively constant.