COPEPOD DIFFUSION WITHIN MULTIFRACTAL PHYTOPLANKTON FIELDS

Oceanic turbulence has been considered for a while as one of the main sources of the heterogeneity of the phytoplankton field over a wide ra nge of scales. However, it is only recently that the intermittency of turbulence has been taken into account, although it is rather indispen sable in the explanation of the observed patchiness of the plankton fi eld. In order to improve the understanding and characterization of the diffusion of copepods within an heterogeneous phytoplankton field, we developed a model based on particle diffusion in a multifractal field . After discussing this model with some detail, we used it and the cor responding numerical simulations in order to investigate the fundament al question: does the strong heterogeneity of the phytoplankton genera te a anomalous diffusion of the copepods? Although a positive answer i s obtained in a rather straightforward manner for a one-dimensional mu ltifractal field of phytoplankton concentration, the answer is rather more involved for a greater (topological) dimension of the field, cont rary to some previous claims. (C) 1998 Elsevier Science B.V. All right s reserved.