EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Effective Diahaline Diffusivities in Estuaries

Hans Burchard1, Ulf Gräwe1, Knut Klingbeil1, Nicky Koganti1, Xaver Lange2, and Marvin Lorenz1
Hans Burchard et al.
  • 1Leibniz Institute for Baltic Sea Research, Physical Oceanography, Rostock, Germany (
  • 2Niels Bohr Institute, University of Copenhagen, Denmark

The present study aims to estimate effective diahaline turbulent salinity fluxes and diffusivities in numerical model simulations of estuarine scenarios. The underlying method is based on a quantification of salinity mixing per salinity class, which is shown to be twice the turbulent salinity transport across the respective isohaline. Using this relation, the recently derived universal law of estuarine mixing, predicting that average mixing per salinity class is twice the respective salinity times the river run‐off, can be directly derived. The turbulent salinity transport is accurately decomposed into physical (due to the turbulence closure) and numerical (due to truncation errors of the salinity advection scheme) contributions. The effective diahaline diffusivity representative for a salinity class and an estuarine region results as the ratio of the diahaline turbulent salinity transport and the respective (negative) salinity gradient, both integrated over the isohaline area in that region and averaged over a specified period. With this approach, the physical (or numerical) diffusivities are calculated as half of the product of physical (or numerical) mixing and the isohaline volume, divided by the square of the isohaline area. The method for accurately calculating physical and numerical diahaline diffusivities is tested and demonstrated for a three‐dimensional idealized exponential estuary. As a major product of this study, maps of the spatial distribution of the effective diahaline diffusivities are shown for the model estuary.

How to cite: Burchard, H., Gräwe, U., Klingbeil, K., Koganti, N., Lange, X., and Lorenz, M.: Effective Diahaline Diffusivities in Estuaries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7712,, 2021.

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