Description of a flexible and extendable physical–biogeochemical model system for the water column |
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Authors: | Hans Burchard, Karsten Bolding, Wilfried Kü hn, Andreas Meister, Thomas Neumann,Lars Umlauf |
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Affiliation: | aBaltic Sea Research Institute Warnemünde, Seestraβe 15, D-18119 Warnemünde, Germany;bBolding and Burchard Hydrodynamics, Strandgyden 25, DK-5466 Asperup, Denmark;cInstitute of Oceanography, University of Hamburg, Bundesstraβe 53, D-20146 Hamburg, Germany;dFaculty of Mathematics and Informatics, University of Kassel, Heinrich-Plett-Str. 40, D-34109 Kassel, Germany |
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Abstract: | A modelling system for coupled physical–biogeochemical simulations in the water column is presented here. The physical model component allows for a number of different statistical turbulence closure schemes, ranging from simple algebraic closures to two-equation turbulence models with algebraic second-moment closures. The biogeochemical module consists of models which are based on a number of state variables represented by their ensemble averaged concentrations. Specific biogeochemical models may range from simple NPZ (nutrient–phytoplankton–zooplankton) to complex ecosystem models. Recently developed modified Patankar solvers for ordinary differential equations allow for stable discretisations of the production and destruction terms guaranteeing conservative and non-negative solutions. The increased stability of these new solvers over explicit solvers is demonstrated for a plankton spring bloom simulation. The model system is applied to marine ecosystem dynamics the Northern North Sea and the Central Gotland Sea. Two different biogeochemical models are applied, a conservative nitrogen-based model to the North Sea, and a more complex model including an oxygen equation to the Baltic Sea, allowing for the reproduction of chemical processes under anoxic conditions. For both applications, earlier model results obtained with slightly different model setups could be basically reproduced. It became however clear that the choice for ecosystem model parameters such as maximum phytoplankton growth rates does strongly depend on the physical model parameters (such as turbulence closure models or external forcing). |
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Keywords: | Numerical modelling Ecosystem modelling Physical– biological interaction Plankton bloom North Sea Baltic Sea ODE solvers |
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