## Wednesday, December 02, 2009

### Power like wind and tides: swimming biosphere

The physics arXiv blog summarized an interesting preprint about the impact of swimmers on the oceans,
Stirring by swimming bodies
Jean-Luc Thiffeault and Stephen Childress begin with a rather surprising fact: the motion of all swimming animals and plants transmits the energy of nearly 1 terajoule per second to the ocean, i.e. 1 TW, close to the power of all the wind and tides!

How much are these swimmers actually contributing to the mixing of the oceans and to their diffusivity? The authors' first order-of-magnitude estimate ends up with a huge number that beats the thermodynamic molecular diffusivity by 3 orders of magnitude. On the other hand, their following models suggest that the mixing is negligible. But the result is very sensitive on detailed properties of the models and it can go both ways.

So even the very question whether the swimmers are more important for the mixing of the oceans than the molecular chaos remains unanswered. This result highlights the complexity of the phenomena in the ocean. Who would have thought that girls and jellyfish may influence the mixing of oceans which could also have consequences for the effective thermal conductivity of the oceans and predictions of the future warming? ;-)