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Mechanisms of estuarine salt plug formation by an along-shelf buoyant current: a numerical model approach
  • Braulio Juarez,
  • Arnoldo Valle-Levinson,
  • Alberto Canestrelli
Braulio Juarez
Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California

Corresponding Author:bjuarez@ufl.edu

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Arnoldo Valle-Levinson
University of Florida
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Alberto Canestrelli
University of Florida
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While estuarine salt plugs can develop worldwide in estuaries adjacent to buoyant coastal currents, their formation has been scarcely documented. This study aims to generalize a mechanism for salt plug formation that does not invoke evaporation processes but involves a buoyant coastal current modified by wind stresses. A numerical model, Delft3D, is used to simulate two idealized bays, one with a single inlet and another with two inlets. The numerical experiments are inspired by recent observations and simulate nine different scenarios of wind and tidal forcings under the influence of an along-shelf buoyant current. Results show that the salt plug induces an inverse circulation at the inlet with inflow at the surface and outflow underneath. This circulation is modified by wind action. The persistence of the salt plug depends on tidal flushing, as well as wind intensity and direction. A yearlong numerical experiment with non-stationary buoyant currents and non-stationary winds indicate that: (i) onshore winds transport oceanic waters into the bay, while offshore winds export estuarine water to the ocean; (ii) onshore winds enhance the inverse circulation at the inlet, while offshore winds stall it. The ratio between wind-driven and density-induced accelerations, given by the Wedderburn number, determines the dominant contribution to the along-estuary circulation in an along-estuary transect. In general, baroclinicity dominates over wind-stress at the inlet, while wind-stress governs the circulation along the estuary. This study represents the first attempt to identify the role of wind and buoyant coastal currents on the dynamics of salt plug formation.
Apr 2022Published in Journal of Geophysical Research: Oceans volume 127 issue 4. 10.1029/2021JC017971