Physical and biological modeling in the Gulf Stream region Part II. Physical and biological processes

Mesoscale physical and biological processes are examined at the Gulf Stream front by means of a 4-D simulation including physical and biological data assimilation. The data assimilated are from Leg 1 of the Fall BIOSYNOP crui se, 21 Sept.-8 Oct. 1988, and GULFCAST data for the same period. Focus is o n the vertical velocities at the front, the vertical and horizontal transpo rts of nutrients and plankton, and the impact of these transports on phytop lankton biomass, production and organic particle export. It was found that while jet meandering enhances new production at the front, primary producti on and phytoplankton concentration at the front are not significantly enhan ced over those of Slope water. Winds during this period also have little im pact on productivity at the front, due to their high temporal variability. Ring-stream interactions, however, significantly increase the net vertical and meridional transports of nutrients and plankton and can lead to phytopl ankton patchiness at the front. This emphasizes the importance of submesosc ale events between interacting mesoscale physical features in the transport of nutrients and plankton, and in explaining the observations. The enhance d phytoplankton concentrations observed during BIOSYNOP are found to be pri marily due to advection (convergence) rather than in situ biological growth . (C) 2001 Elsevier Science Ltd. All rights reserved.