WIND FORCED BIOLOGICAL-PHYSICAL INTERACTIONS ON AN ISOLATED OFFSHORE BANK

Large advective losses of bank water during winter due to strong wind forcing are hypothesized to be a significant factor limiting recruitme nt of spring spawning plankton and subsequent feeding success of larva l fish. The plausibility of this ''washout hypothesis'' is examined us ing numerical models of plankton and physical dynamics on an idealized off-shore bank, approximating conditions on Georges Bank. A semi-spec tral primitive equation model (SPEM) is used to study three-dimensiona l wind- and density-driven circulation. Biological models were used to represent: (1) a single generation of copepods; and (2) a simple plan ktonic food chain. No migration or swimming behavior was included in a ny of the models. Results indicate that the typically high winds durin g winter (velocity: 13 m s-1; duration: 20 days) can cause significant replacement of the bank water mass with surrounding waters. This larg e exchange causes major reductions in zooplankton populations and zoop lankton and phytoplankton production over the bank. These alterations in bank trophic structure reduce the energy transfer from primary prod uction to secondary production and may lead to poor recruitment at hig her trophic levels.