Plankton dynamics controlled by hydrodynamic processes near a submarine canyon off NW corsican coast: A numerical modelling study

摘要

A three-dimensional (3D) non-linear high-resolution hydrodynamic model coupled to a coastal plankton ecosystem model is used to estimate the impact of hydrodynamic processes on the evolution of the spring phytoplankton bloom in the vicinity of a submarine canyon. Model results for the plankton distribution showed a clear 3D character around and in the canyon, with large horizontal and vertical gradients, induced by the hydrodynamic constraints. Phytoplankton concentrations were significantly larger all along the slope domain with maximum values obtained over the canyon. Upwelling of deep water rich in nitrate takes place both upstream (with respect to the current direction normal to the central axis of the canyon) and downstream of the canyon enhancing primary production. As phytoplankton-rich water enters into the western part of the canyon it is downwelled and trapped by the cyclonic circulation leading to accumulation of phytoplankton biomass there. The effect of wind events was to induce an upward nitrate flux into the upper layer through vertical turbulent diffusion, allowing the start of a short-live phytoplankton bloom. Maximum surface nitrate concentrations were found along the slope and particularly upstream and downstream of the canyon just after the wind stopped. Enhanced turbulent diffusion combined with upwelling motion in these areas resulted in larger upward nitrate transports, further enhancing primary production. (c) 2006 Elsevier Ltd. All rights reserved.