A zooplankton diel vertical migration parameterization for coastal marine ecosystem modeling

Abstract. A simple parameterization of zooplankton vertical swimming is proposed as a way to reproduce the diel vertical migration (DVM) behavior, which refers to the daily descent of aquatic organisms hundreds of meters below the surface at dawn and their return to the surface at dusk, a phenomenon that is widespread among most zooplankton species. The swimming behavior is mechanistically parameterized as a function of the local irradiance and food availability, and is incorporated in a simple biogeochemical model coupled with a water column turbulence model in an Eulerian framework. The DVM behavior and its impact on plankton dynamics are investigated in an idealised configuration representing a marine coastal ecosystem. The sensitivity of the model to key parameters such as the zooplankton swimming speed, grazing rate, the optimal irradiance and turbulent diffusivity is evaluated with respect to three metrics representing the actual DVM behavior, the zooplankton-to-phytoplankton grazing coupling efficiency, and the vertical carbon export. Results show that the parameterization is able to reproduce the main characteristics of present knowledge about zooplankton DVM, and that the associated ecosystem responses are strongly sensitive to the maximum grazing rate, and moderately sensitive to other parameters.