Colloquium on May 2, 2011

Ulrike Feudel
Carl von Ossietzky Universität Oldenburg

Patterns in the ocean resulting from the interplay between hydrodynamics and biology

Spatio-temporal patterns in marine systems are a result of the interaction of biological and chemical processes with physical transport. In the water column large/mesoscale advection and small scale turbulence are the dominant physical processes. We demonstrate with two examples how hydrodynamic flows on different scales affect the biology:
1) Studying the von Karman vortex street in the wake of an island we show how the upwelling of nutrients away from the island influences the evolution of plankton close to the island. In particular we show that mesoscale vortices act as incubators for plankton growth leading to localized plankton blooms within vortices. Additionally, the dominance of different species in the ocean can be a result of the interplay between the flow and the biological growth.
2) To demonstrate the impact of small scale turbulence we present a coupled model for advection, aggregation and fragmentation that is based on the dynamics of individual, fractal-like inertial particles in random flows. Due to the particle inertia advection leads to the accumulation of the particles in certain regions of the flow. Aggregation upon collision of particles and fragmentation due to hydrodynamical shear leads to a steady state size distribution of the aggegates which depends crucially on the considered mechanism of fragmentation.  We demonstrate how the fractal fractal dimension and well as the binding strength of the aggregates influences the shape of the resulting size distribution.