A numerical model of mesoscale frontal instabilities and plankton dynamics- I. Model formulation and initial experiments

Previous observational and modelling studies of open ocean frontal regions have found large Vertical velocities associated with instabilities on the f rontal jet. A combined physical/ecosystem numerical model is used to invest igate the impact of jet instability and the associated vertical motions on the local ecosystem. The evolution of the instability of a mesoscale fronta l jet gives rise to vertical transport of nutrients into the euphotic zone and subduction of biota out of the euphotic zone. The upwelling of nutrient s stimulates increases in primary production, with resulting increases in p hytoplankton stocks. The reaction of the ecosystem is found to be dependent on the physical characteristics of the front, but the increase in primary production can be locally of the order of 100%, and of the order of 10% whe n averaged over the frontal region. The action of upwelling and subduction introduces spatial heterogeneity in primary production and plankton biomass . The heterogeneity is at a variety of length scales, from the order of a f ew kilometres for thin filaments and up to 50 km for coherent features. Wit h increases in new production occurring over several degrees of latitude, f rontal dynamics may make a significant contribution to the strength of the biological pump. (C) 2000 Elsevier Science Ltd. All rights reserved.