Friday, July 31, 2009

Jellyfish; The Spoons of the Sea

When to the new eyes of thee
All things by immortal power,
Near or far,
To each other linked are,
So that thou canst not stir a flower
Without troubling a star...........

(Francis Thompson)

NEXT time you go for a dip in the sea, bear in mind that your deft front crawl is helping to mix up the waters. In fact, marine life may be stirring the oceans and moving nutrients around as much as winds or tides.

According to a theory proposed by Darwin's grandson, Charles Galton Darwin, a body moving through water drags some of the fluid with it.

Darwin's Drift

In "Darwin drift", a high-pressure zone forms at the front of each swimming animal, leaving an area of lower pressure behind, which draws in adjacent water. This results in a net movement of fluid in the direction of the swimmer.

Swarms of Jellyfish

To test the idea, Kakani Katija and John Dabiri at the California Institute of Technology in Pasadena went to a lake in the Republic of Palau in the Pacific Ocean. Diving among swarms of jellyfish, the pair used suspended dyes and a newly designed laser velocimeter to measure the movement of water around the jellyfish. They found that the animals did indeed drag water with them as they swam (Nature, vol 460, p 624).

Mixing Energy

The researchers then estimated the total energy that all ocean swimmers impart on the water. They calculated that it was on a par with the mixing energy imparted by winds or tides. The findings suggest ocean swimmers can move water over long distances and that they could help run the vertical currents that push nutrients around between the sea floor and surface waters.

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