Project Summary

Peter Franks and Changsheng Chen

U.S. GLOBEC III: Process Modeling Studies of Plankton and Larval Fish in the Tidal-Mixing Fronts of Georges Bank

This is a joint proposal submitted by the Marine Life Research Group at the Scripps Institution of Oceanography, and the Department of Marine Sciences at the University of Georgia.

In the proposed study we intend to continue our exploration of the physical-biological couplings on Georges Bank, focusing on the physical, physiological and behavioral dynamics at the two-dimensional and three-dimensional tidal fronts surrounding Georges Bank. The goals of the proposed work will be to

1. understand the influences of bottom topography, the sloping bottom boundary layer, and stratification on the plankton and larval cod and haddock on Georges Bank;

2. elucidate the three-dimensional structure of physical and biological properties on Georges Bank, and quantify the along- and cross-front gradients;

3. understand the effect of perturbations to the physical and biological dynamics at the Georges Bank tidal mixing fronts, including the spring-neap tidal cycle and changes in stratification;

4. quantify the relative impacts of biological, physical and behavioral dynamics on observed distributions of properties on Georges Bank.

These objectives will be achieved using a hierarchy of two- and three-dimensional models, incorporating data gathered during phases I, II and III of the U.S. GLOBEC Georges Bank study. The model architecture is based on the primitive-equation/turbulence-closure/ecosystem model developed by the PIs during previous GLOBEC-funded work. These models will use both idealized and realistic topography and forcings, including a recently developed three-dimensional physical-ecosystem regional model of the Gulf of Maine and Georges Bank.

Previous work by the PIs has shown this model architecture capable of accurately reproducing the tidally forced physical and biological dynamics on Georges Bank. This work must now be expanded to quantify the physical and biological dynamics controlling cross-frontal exchange and patchiness at the Georges Bank tidal fronts. We will examine the effects of bottom topography, stratification, heat flux, wind stress and behavioral dynamics in controlling patterns and fluxes of the plankton. The effects of these forcings on the target species of larval cod and haddock will be studied by coupling a metabolic model of larval fish to the physical-ecosystem model. The larval fish model incorporates temperature, food and turbulence dependence of growth.

The proposed research will make the following contributions to the U.S. GLOBEC Georges Bank Study and the oceanographic community:

1. the combination of idealized and realistic model studies will significantly increase our understanding of the temporal and spatial dynamics of physical-biological coupling on Georges Bank and other regions of strong bathymetry, strong tidal forcing, and variable surface forcing;

2. the proposed models will be entirely complementary to the field studies being proposed during GLOBEC Phase III, and will form a synergistic link between the various modes of investigation into frontal dynamics on Georges Bank;

3. the combination of physical and biological models will significantly increase our understanding of the factors influencing the growth and recruitment of larval cod and haddock on Georges Bank; and

4. the testing of model simulations with field data will allow us to reject inadequate models, improve model architectures and forcings, recognize limitations of the models, and suggest improved data collection strategies.