Application of variational data assimilation to coupled physical-biological models of the North Atlantic Bloom

Lagrangian floats and seagliders were deployed in the North Atlantic region south of Iceland from late March to early July 2008 and provided 3-D coverage of the spring bloom over time. The measured physical, chemical and bio-optical data, calibrated with data collected on three supporting cruises, is used to develop an ecosystem model describing the bloom and its associated carbon fluxes. The model's physical framework is based on the 1-D General Ocean Turbulence Model (GOTM) which is set up for a North Atlantic site at 60°N, 20°W and forced with data on wind speed, air pressure, air temperature and humidity. Initially, we coupled this physical model to an NPZD biological model with dynamic chlorophyll added. The model was then extended to include a silica cycle and diatoms as a separate phytoplankton group in order to simulate the presumed effect of silicate depletion on diatom sinking. We determined the biological parameters that are most important for model behavior through a sensitivity analysis and will apply variational data assimilation to optimize these model parameters and systematically assess the model-data consistency of the different model variants. The final model will be used to estimate carbon fluxes and export during the bloom.