Phytoplankton dynamics in the English Channel: a simplified three-dimensional approach

A physical model has been built to account for the main physical features of the English Channel, in both horizontal and vertical dimensions. It combines a long-term residual model and a vertical thermal model, dividing the water column into ten levels. Its simplicity provides relatively rapid simulations of phytoplankton dynamics over a large area and appears to be sufficient to represent the physical structure of the Channel. Thus, the yearly evolution of ecosystem dynamics can be studied. Results from the simulation highlight the influence of thermal stratification occurring in the western part of the area, since the vertical structure of the water column mainly determines the date of the spring bloom. In the eastern English Channel, the main characteristic is the influence of nutrient supply from the river Seine and the corresponding high chlorophyll concentrations. This study also allowed us to compare results from this model and those from a previous box-model. The approaches appear to be complementary, since the former provides more accurate results and the latter enables long-term simulations to be made.