© 1997 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
New models for the exploration of biological processes at fronts
Marine Life Research Group, Scripps Institution of Oceanography, University of California San Diego La Jolla, CA, 92093-0218, USA. E-mail: pfranks{at}ucsd.edu
The use of models in the exploration of biological processes at fronts has been limited by the poor representation of boundary-layer processes. The strongly sloping pycnocline of frontal regions forces very different buoyancy and momentum fluxes on either side of the front. This cross-frontal contrast in the vertical mixing of heat or momentum by wind or bottom stress couples to the horizontal velocities, creating non-linear cross-frontal flows. These vertical and horizontal motions have immediate impacts on the spatial and temporal patchiness of biological properties at fronts. New model architectures now couple more accurate representations of turbulent mixing in boundary layers with traditional primitive-equation models. Recently, these coupled primitive-equation/mixed-layer models have been integrated with simple ecosystem models to explore the dynamics of biological processes at fronts. I describe two different architectures of these coupled models: a slab mixed-layer/primitive-equation/ecosystem model, and a turbulence-closure mixed-layer/primitive-equation/ecosystem model. These models have been applied to a wind-forced front and a tidal front respectively. The scales of physical features and biological patchiness described by the models with mixed-layer physics are quite different, usually smaller, than the scales predicted by the primitive-equation models alone. Resolution of vertical processes is significantly enhanced by the inclusion of mixed-layer physics, contributing to a more accurate description of biological dynamics at these intermediate scales.
Keywords: fronts, mixed-layer models, patchiness
Received 12 January 1996; accepted 8 August 1996.