A 3D SPM model for biogeochemical modelling, with application to the northwest European continental shelf

An SPM resuspension method was developed for use in 3D coupled hydrodynamics-biogeochemistry models to feed into simulations of the under-water light climate and and primary production. The method uses a single mineral fine SPM component for computational efficiency, with a concentration-dependent settling velocity to parameterize the effect of settling of different size fractions. The SPM is resuspended in response to combined wave and current conditions. Wave conditions were calculated using a simple set of equilibrium equations, which allows computationally cheap inclusion of the large-scale spatial and temporal trends of the wave field. The development was carried out using 1D water-column implementations of GOTM-ERSEM-BFM for two sites for which multi-year time series observations from autonomous moorings (SmartBuoy) were available. A sensitivity study is included to illustrate the effect of the main variables controlling the exchange with the sea-bed and the settling velocity. The method was applied to a 3D model implementation of GETM-ERSEM-BFM for the north-west European continental shelf, comparing mineral fine SPM concentrations at five sites with SmartBuoy observations, and shelf-wide using remote sensing. The 3D implementation included a simple fitting method to generate gridded sea-bed composition information for use in the sea-bed boundary conditions. The results showed that the model produces reasonable simulations of seasonal SPM concentrations across the northwest European continental shelf.