MACROSCALE ECOHYDRODYNAMIC MODELING ON THE NORTHWEST EUROPEAN CONTINENTAL-SHELF

A 3D coupled hydrodynamic-biological model is applied to the simulatio n of the biological processes on the Northwest European Continental Sh elf. The model operates in the macroscale spectral window (time scales of a month or a season) without explicit description of the higher fr equency processes but with an adequate modeling of their influence on larger time scales. The hydrodynamic sub-model is 3D, baroclinic and i ncludes a refined turbulence closure. The non-linear interactions of m esoscale fluctuations are described by means of the generalized mesosc ale Reynolds stresses and the Stokes drift transport velocity field. T he biological sub-model describes the nitrogen and carbon cycles throu gh the food web with 17 state variables representing 9 compartments: i norganic nutrients, small phytoplankton, large phytoplankton, dissolve d organic matter, pelagic bacteria, heterotrophic flagellates, pelagic detritus, zooplankton and benthic organic detritus. The simulation em phasizes the strong influence of the local depth and of the stability of the water column on the whole annual cycle of phytoplankton. In wel l-mixed shallow areas, the chlorophyll concentration increases in earl y spring and the primary production occurs steadily until October. In deeper areas, the spring bloom is much sharper and appears later, afte r the set up of the seasonal stratification. The main part of the prim ary production happens during the bloom period. The macroscale approac h provides results that are comparable with observations and results o f other more classical models describing explicitly the higher frequen cy processes. The current method allows, however, a more direct insigh t into the dynamics of the system and into the interactions between th e hydrodynamics and the biology. Also, it greatly reduces the CPU requ irements and is therefore particularly suited for repeated or long ter m simulations. (C) 1998 Elsevier Science B.V. All rights reserved.