A Coupled Physical-Chemica I-Biological Model for the
Western Baltic
K. Fennel and T. Neumann
1
Introduction
The shallow and strongly stratified Baltic Sea, with only narrow channels to
the North Sea is very sensitive to anthropogenic influences. Increased nutrient inputs during the last decades have led to a significant eutrophication especially in the nearshore regions (Nehring 1992; Nehring and Matthiius 1991;
Wulff 1990). Indications of changes in the phytoplankton biomass and species
composition have been reported (Schulz and Kaiser 1986; Wulff et al. 1990).
The Baltic Sea is characterized by a high variability of physical, chemical
and biological parameters on mesoscale and other spatial and temporal
scales. Natural variations, mainly caused by fluctuations of the hydrographical conditions, overlie longterm changes. Stratification, topography, vertical
mixing, mesoscale circulation patterns, external forcing as well as chemicalbiological transformations between the various inorganic and organic compounds are controlling factors for changes in the total amount and distribution of nutrients and plankton. Complex non-linear interactions exist between the compartments of the ecosystem. A better understanding of the interactions of physical transport processes and chemical-biological dynamics
is required. A coupled chemical-biological and circulation model is used for
the western Baltic to study the effects of variable physical forces on the dynamics of nutrients and plankton (Fennel and Neumann 1996). The most important compartments of the system are included so that the model is able to
grasp the interactions of mesoscale transport processes and chemical-biological transformations.
Model simulations over 3 months were performed for two years, 1994 and
1995, with realistic external forcing to investigate interannual and regional
differences in the dynamics of nutrients and plankton. In addition, model experiments with different horizontal resolution were carried out to investigate
the influence of grid resolution.
Western Baltic
K. Fennel and T. Neumann
1
Introduction
The shallow and strongly stratified Baltic Sea, with only narrow channels to
the North Sea is very sensitive to anthropogenic influences. Increased nutrient inputs during the last decades have led to a significant eutrophication especially in the nearshore regions (Nehring 1992; Nehring and Matthiius 1991;
Wulff 1990). Indications of changes in the phytoplankton biomass and species
composition have been reported (Schulz and Kaiser 1986; Wulff et al. 1990).
The Baltic Sea is characterized by a high variability of physical, chemical
and biological parameters on mesoscale and other spatial and temporal
scales. Natural variations, mainly caused by fluctuations of the hydrographical conditions, overlie longterm changes. Stratification, topography, vertical
mixing, mesoscale circulation patterns, external forcing as well as chemicalbiological transformations between the various inorganic and organic compounds are controlling factors for changes in the total amount and distribution of nutrients and plankton. Complex non-linear interactions exist between the compartments of the ecosystem. A better understanding of the interactions of physical transport processes and chemical-biological dynamics
is required. A coupled chemical-biological and circulation model is used for
the western Baltic to study the effects of variable physical forces on the dynamics of nutrients and plankton (Fennel and Neumann 1996). The most important compartments of the system are included so that the model is able to
grasp the interactions of mesoscale transport processes and chemical-biological transformations.
Model simulations over 3 months were performed for two years, 1994 and
1995, with realistic external forcing to investigate interannual and regional
differences in the dynamics of nutrients and plankton. In addition, model experiments with different horizontal resolution were carried out to investigate
the influence of grid resolution.