Prof. Hans Pecseli (Fysisk institutt, UiO): "Turbulence in the oceans and the biological food chain"

Fredagskollokvium

Abstract

Micro-organisms in the oceans, fish larvae and similar (here called "predators"), have only little motion of their own, and it can safely be assumed that they are passively carried along by the local flow velocity, at least to a good approximation. Similarly, it can be argued that their food (micro-zooplancton, for instance, here called "prey") is also passively convected by the same flow. It is then rather evident that such micro-organisms will eventually be starving, unless motions in the water changes the predator-prey separations, and brings, at least from time to time, some prey within reach of the predators. Closer inspection of the problem demonstrates that the water has to be in a relatively strongly turbulent state in order to achieve this.

Fortunately, the motion of particles in turbulent flows has been investigated in great detail, in part because of the strong environmental importance of the problem. A wealth of data are available for these types of phenomena, and it will be demonstrated how some of these data can be utilized in a simple way, in order to get insight also into the present problem. The existence of seemingly universal scaling laws for the average prey flux to a selected predator can be demonstrated. These laws depend on the radius in a suitably defined "reach of interception", as well as on the intensity of the turbulence. Some of these scaling laws are in contradiction with our intuitive expectations.

Publisert 12. aug. 2009 10:50 - Sist endret 15. juni 2011 13:48