Coupled physical–biological modelling study of the East Australian Current with idealised wind forcing: Part II. Biological dynamical analysis

A northerly and a southerly wind simulation of a coupled physical–biomechanical NPZ model configured for the East Australian Current (EAC) are analysed using the relative size of dynamical terms in the biological equations. The NPZ model is a configuration of the Baird et al. [Baird, M.E., Oke, P.R., Suthers, I.M., Middleton, J.H., 2004. A plankton population model with bio-mechanical descriptions of biological processes in an idealised 2-D ocean basin. J. Mar. Syst. 50, 199–222.] model with biomechanical descriptions of phytoplankton and zooplankton processes. Analysis of the complete set of dynamical terms affecting the biological model are presented, including: advection, diffusion, nutrient uptake and light capture, phytoplankton and zooplankton growth, grazing, and mortality, as well as the local rate of change, or tendency, of the biological state variables. A dynamical analysis is undertaken at two scales: (1) at the scale of an individual phytoplankton cell of the interaction of light supply, nutrient supply and organic matter synthesis in determining internal nitrogen and energy reserves, and (2) at the ecosystem scale of phytoplankton and zooplankton growth in determining dissolved inorganic nitrogen, phytoplankton and zooplankton concentrations. The spatial distribution of primary and secondary production, an approximation of the f-ratio, and continental shelf fluxes of inorganic and organic nitrogen are also investigated. As found in Part I of this study, the tracer age provides a useful diagnostic tool for understanding the affects of the physical forcing on biological processes. The analysis provides a quantification of the biological processes occurring off the NSW shelf at a spatial scale and interpretive detail which is not possible with the limited in situ sampling of the region.