TURBULENCE, DIFFUSION AND PATCHINESS IN THE SEA

We explore the role that biological processes play in the patchiness of plankton populations in the sea. We ask how population interactions modify the variance in plankton density as a function of spatial scale (i.e. the variance spectrum) from that expected if the biota were merely passive tracers. Using an approximate model for two limiting cases of turbulence - the inertial subrange and two-dimensional turbulence - we consider a simple predator - prey formulation for interacting populations in a turbulent ocean. No simple generalizations emerge. The interacting populations 'redden' (i.e. more variance at large scale) the spectrum of the passive tracers in the inertial subrange. Conversely, the interaction 'whitens' (i.e. less variance at large scale) the passive tracer spectrum for two-dimensional turbulence. This mirrors results in terrestrial environments.