A 3-dimensional primary production model (BLOOM/GEM) and its applications to the (southern) North Sea (coupled physical–chemical–ecological model)

Abstract This paper presents the ecological modelling instrument BLOOM/GEM and several applications to the southern North Sea, including a 3-dimensional model validation. The current instrument and its predecessors have been used since the 1980s for evaluating the ecological status of the North Sea and potential effect of management strategies. The main modelled processes of nutrient cycling, oxygen dynamics and primary production are described, as well as the external forcings required for the ecological model (hydrodynamics, suspended sediments and river loads). In the development of the BLOOM/GEM modelling instrument, the explicit choice of processes to include (the ‘ ecological’ resolution) has been balanced with the need for high spatial resolution in the model applications for the Dutch coastal zone. The calibration and validation of the BLOOM/GEM modelling instrument as well as the model applications have mainly drawn on the extensive dataset available for the Dutch coastal waters ( http://www.waterbase.nl ). A specific 3-dimensional model application to the North Sea is described including the model validation results based on the use of an objective cost function for a number of different substances. Plotted model results showing seasonal as well as regional variations and spatial gradients for many substances at several stations give additional support to the validation. As such, the model is well suited to support many management decisions, related to e.g. the OSPAR convention and the European Water Framework Directive and the construction of infrastructural works.