Warnemünde Turbulence Days 2005

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(28.09. - 30.09.2005)


“Impact of small-scale physics on marine biology.”
Contributions to this topic including theories, observations, laboratory scale experiments and numerical simulations will be welcome.

Marine life is affected by small-scale physical processes in many ways and on many scales.

Mixed layer scale, inertial subrange:
Most classically, the vertical mixing effect of small-scale turbulence on the mixed layer scale has led to the well-known algal bloom theories of critical depth and critical turbulence. Also the mixing of nutrients across pycnoclines due to various small-scale processes is well-accepted, leading to sub-surface chlorophyll maxima.

Viscous subrange:
On much smaller scales, aggregates of phytoplankton, bacteria and dead organic material play an important role for the ecosystem. Their size is controlled by the size of the smallest turbulent eddies, but their generation is also dependent on the turbulence level: too low turbulence minimises the number of encounters between various particles. Phytoplankton and zooplankton patchiness is function of biogeochemical processes, but is also strongly dependent on the small-scale turbulence.

Viscous scale:
Phytoplankta and small zooplankta generally live in a viscous world. Nonetheless, their life is strongly determined by turbulence. Single phytoplankton cells experience complicated journeys through the mixed layer, moving them away from their favourite light level. Turbulence not only moves them around, but also turns them upside down. Stronger small scale shear decreases the size of their halo depleted from nutrients. Strong turbulence increases the encounters between predator and prey. However, too strong turbulence prevents the predators to sense their prey. Many individuals try to find an optimal level of turbulence. Some larger zooplankta enjoy between a viscous and a turbulent world. Their individual Reynolds number may be significantly larger than unity, depending on their swimming speed. Furthermore, coherent structures in the flow field may be important for their activity, such as maiting and feeding.

It is a challenge for the next decade to increase the understanding of these processes by means of modern instrumentation and experiments in the ocean, the laboratory and on the computer.