| Planktonic organisms, as long as they have a density similar to the water mass, are in first order approximation generally considered as drifting with the surrounding water mass. Their inertial particle character is typically neglected. This approach is doubtless right for the large advective scale. However, for smaller scale flow field structures and their impact on plankton drift, which are in oceanography typically parameterized by a turbulence closure approach, this is not any more the case, a circumstance very relevant for the vertical placement for planktonic organisms in the water column and hence for their larger scale drift. How the impact of small scale turbulence on particle motion has to be parameterized is currently unclear, but it is unclear that observed patter structures in planktonic distributions can not be reproduced by a models when using a divergence-free approach for the turbulence, ensuring holding of divergence free particle drift. Biologists typically explain this by proper motion of the planktonic organisms. However, this ought not to be the only explanation. The physical forcing on an inertial particle could be responsible for most of the structures found. Here some biological observations will be presented and the problem of parameterization will be discussed while presenting different model results. The larger scale structures achieved for a realistic basin application in the German Bight will be discussed and compared to observations. Furthermore the related problem of small scale forcing on juvenile brown shrimps and the utilization of it for the survival strategy will be discussed. |
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