A depth-resolving numerical model of physically forced microbiology at theEuropean shelf edge

SEDBIOL, a 1-D depth-resolving model, which couples physical, microbiologic al, and sedimentation/resuspension submodels, is described. The physical su bmodel uses a level 2 turbulence closure scheme forced by meteorology and t idal elevations to provide seasonally varying turbulent diffusivites. Withi n this framework is placed a model for water column microbiology, which inc ludes the cycling of nitrogen and carbon through microplankton (phytoplankt on and pelagic microheterotrophs) and detrital compartments. The microbiolo gical system is closed by mesozooplankton grazing pressures taken from obse rved zooplankton abundance. Inorganic and organic (microplankton and detrit us) light-attenuating particulates sink through the water column depositing at the seabed to form a superficial layer of 'fluff' from which they can b e resuspended. The model has been used to simulate conditions on the Goban Spur (49.5 degr ees N 10.5 degrees W) in 200 m of water, using climatological meteorologica l forcing, M2 tidal dynamics and zooplankton data from the Continuous Plank ton Recorder (CPR) Survey. The results were compared with observed temperat ure, chlorophyll, nitrate and annual primary production data taken as part of the CEC MAST II Ocean Margin EXchange (OMEX) project, and with remotely sensed chlorophyll. The physical submodel was calibrated against observed t emperature profiles, and its fit improved by adding 'pseudo-weather' and a relaxation term for deep-water temperature, and by increasing the value of 'background' eddy coefficients. The sensitivity of the microbiological mode l to changes in the physical environment and several key parameters has bee n tested, with values improved by fitting simulations to observed chlorophy ll and nitrate concentrations. The coupled model was used to predict annual net primary productivity, carbon fluxes into near-bed and fluff layers and to compare the magnitude of biological and physical terms. (C) 2000 Elsevi er Science B.V. All rights reserved.