Importance of resuspended sediment dynamics for the phytoplankton spring bloom in a coastal marine ecosystem

Accurate model estimates of primary production in coastal and shelf waters are challenged by the high temporal and spatial variability of suspended sediment dynamics. It is therefore still unclear how light climate shapes spatio-temporal patterns in near-coast chlorophyll-a (Chl-a) concentration. In order to identify an effective representation of light extinction due to suspended particulate matter (SPM) in ecosystem models, we integrate different formulations of light attenuation into a coupled physical–biological model of the German Bight. The model describes Chl-a as well as phytoplankton–zooplankton interactions and calculates physical transport using the General Estuarine Transport Model (GETM). Parameters of the ecosystem module were calibrated using a 0D setup constrained by available measurements at Helgoland Roads. The comparison between data and simulations shows that the model, despite its simplicity, is capable of reproducing the development of the spring bloom in 2003. We propose a novel application that uses MERIS-derived spatial data to constrain the parameterisation of light extinction and compare different scenarios of light attenuation as determined by phytoplankton self-shading, yellow substances and SPM dynamics. Our work highlights the sensitivity of calculated autotrophic growth to water depth, salinity fronts and sediment transport. We found that the accuracy of SPM-forcing is only critical at the onset of the bloom.