caa a22 4500 605546657 CHVBK 20210128100942.0 cr unu---uuuuu 210128e20151201xx s 000 0 eng 10.1007/s10236-015-0895-x doi (NATIONALLICENCE)springer-10.1007/s10236-015-0895-x Thermohaline residual circulation of the Wadden Sea [Elektronische Daten] [Hans Burchard, Thomas Badewien] In this study, we present estuarine circulation driven by horizontal density gradients generated by spatially homogeneous surface buoyancy fluxes over sloping bathymetry as a dynamical feature in the coastal zone being potentially relevant for cross-coastal transports. A combination of downward buoyancy flux (net precipitation, net heating) together with tidal mixing may generate a classical estuarine circulation with landward near-bottom residual currents. The Wadden Sea of the south-eastern North Sea is a prototype for such a coastal regime. It is characterised by extensive inter-tidal flats along the coast separated from the open sea by barrier islands. Here, we present long-term observations from the Wadden Sea covering the years 2006-2011. We investigated the statistics of the density gradients. Typical values for the landward density gradient were ∂ x ρ≈−3⋅10−5 kg m−4 and maximum values were ∂ x ρ≈−6.5⋅10−5 kg m−4. The magnitude of the density gradient resulted from the magnitude of the salinity gradient, with some modifications by the positive (towards the coast, in spring) or negative (towards the sea, in autumn) temperature gradient. To explain the generation of estuarine circulation by the surface buoyancy flux, we construct an analytical model representing the geometry and dynamics of a Wadden Sea Basin. With downward buoyancy flux, a weak classical estuarine circulation due to gravitational forcing results, whereas upward buoyancy flux drives inverse estuarine circulation. Finally, a two-dimensional (vertical-longitudinal) numerical model was set up for the idealised geometry, including tidally asymmetric turbulent mixing. This results in significantly stronger estuarine circulation due to the presence of tidal straining. The model assesses the circulation due to neutral and upward surface buoyancy fluxes. We conclude that these mechanisms may be important in many coastal areas and may substantially contribute to coast-to-sea exchange in these areas. Springer-Verlag Berlin Heidelberg, 2015 Wadden Sea nationallicence Estuarine circulation nationallicence Surface buoyancy flux nationallicence Horizontal density gradients nationallicence Burchard Hans Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, D-18119, Rostock, Germany aut Badewien Thomas Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Schleusenstraße 1, D-26382, Wilhelmshaven, Germany aut Ocean Dynamics Springer Berlin Heidelberg 65/12(2015-12-01), 1717-1730 1616-7341 65:12<1717 2015 65 10236 https://doi.org/10.1007/s10236-015-0895-x text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10236-015-0895-x text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Burchard Hans Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, D-18119, Rostock, Germany aut NATIONALLICENCE 700 1- Badewien Thomas Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Schleusenstraße 1, D-26382, Wilhelmshaven, Germany aut NATIONALLICENCE 773 0- Ocean Dynamics Springer Berlin Heidelberg 65/12(2015-12-01), 1717-1730 1616-7341 65:12<1717 2015 65 10236