Assessment of three-dimensional physical-biological ECOHAM1 simulations by quantified validation for the North Sea with ICES and ERSEM data

Abstract

The Ecological North Sea Model, Hamburg Version 1 (ECOHAM1) simulates phosphorus-related phytoplankton processes in relation to the physical dynamics of the North Sea. This three-dimensional model calculates annual primary production, the main related processes in the North Sea and regional variations on a 20 km2 basis, and at 5 m vertical resolution. The simulation for 1985 was driven by the actual physical forcing that occurred, and took into account monthly river loads from 14 rivers, the daily velocities and diffusivities from a baroclinic North Sea model, and solar radiation calculated every 30 min. The high level of variability of the forcing generates considerable variability in physical and biological dynamics. The simulated chlorophyll and phosphate concentrations were validated by a cost function, normalized in units of standard deviation of data. The validation with ICES data indicates how well the model performs over a coarse time and spatial scale of 1°x 0.5°boxes with long-term seasonal averages. The phosphate cost functions for the three seasons are: 1.03 in winter, between 1.51 and 1.99 in spring, and between 1.85 and 1.9 in summer. Horizontal distributions of the cost function for phosphate and chlorophyll are presented. An additional validation step is the evaluation of annual cycles in specific locations of the ERSEM boxes of 1°x 1°. The ERSEM data consists of climatological monthly means. The annual cycle for a box in the German Bight shows a cost-function value of 2.21, and for the Dutch coast a value of 1.27. The main difficulty of the model is calculating correctly the winter and early spring chlorophyll concentrations. (C) 2000 International Council for the Exploration of the Sea.