Simulations of Plankton Dynamics on the Scotian Shelf

We are developing models of shelf plankton dynamics towards their eventual use to prescribe the boundary conditions for environmental models of Lunenburg Bay.

The model reproduces the plankton seasonal cycle on the middle shelf and the increasing spring blooms from 1999 to 2004. We are currently evaluating the model for inner shelf areas more representative of the boundary with Lunenburg Bay.


Because Lunenburg Bay is an open embayment, simulations of the Bay plankton ecosystem will require concurrent simulations of the plankton ecosystem on the adjacent shelf. We use actual weather data to simulate physical conditions (temperature, salinity, turbulence) in a vertical column which then provide the simulated environment for a plankton ecosystem model. We use this one-dimensional test bed to evaluate different formulations for the ecosystem model by comparing the simulated results to a time series of ecological data gathered at a monitoring station near the mouth of Halifax harbour. For example, we found that the formulation used to describe grazing of phytoplankton (microscopic plants) by zooplankton (minute herbivores) had a strong impact on the realism of the simulations. Using the best formulation allowed us to reproduce not only the seasonal cycle of plankton booms and busts but also the inter-annual variability in the strength of the plankton blooms (Figure 1). We are testing this model at more sites towards an eventual incorporation of part or whole of this model into circulation models of Lunenburg Bay and the adjacent shelf.

A.F. V├ęzina¹,², B. Casault¹, M. Pahlow² and H . Maass¹
¹ Bedford Institute of Oceanography, Dartmouth, N.S.
² Oceanography Department, Dalhousie University, Halifax, N.S