Application of model reduced 4D-Var to a 1D ecosystem model

► Model reduced 4D-Var capable of combined parameter and initial condition calibration for ecosystem. ► Initial condition estimated in the reduced space, which significantly decreases the size of the control vector. ► High quality of the reduced model is not necessary to obtain high quality estimations in data assimilation experiments. ► Model reduced 4D-Var method is a potential tool for large ecosystems.