Jellyfish stirring things up.

02 August 2009
Posted by Chris Smith.

Jellyfish may spend their lives passively drifting through the open oceans at the mercy of currents and tides, but they could also be stirring things up as they go.

JellyfishTogether, all the swimming things in the oceans - including minute plankton - could contribute as much mixing as the winds and tides. That's according to KakaniKatijaand JohnDabiri from the California Institute of Technology in Pasadena who's study appeared this week in the journal Nature. It could mean that climate modelers have been missing an important part of the puzzle.

Katija and Dabiriused computer models to investigate a process in which a body moving through a fluid pulls some of that fluid with it. The more sticky or viscous the fluid is, the more of it is pulled along. This was an idea first reported 50 years ago by Charles Darwin - grandson of famous author of On the Origin of Species.

The computer models showed that a tiny plankton pulls up to four times its volume in water by just moving a few body lengths.

The research duo then set off for Palau, a cluster of beautiful tropical islands in the Pacific, to test out their ideas among swarms of real jellyfish: a very sensible choice because there jellyfish living in land-locked marine lakes have evolved to have no sting.

They squirted luminous dye behind of the jellyfish and filmed them using special laser-equipped underwater cameras. They watched as each jellyfish was followed by a trail of glowing dye. It turns out that up to 90% of the water movement came down to Darwin's theory and not because of a turbulent wake streaming behind the jellyfish.

The big question now is how this translates to a global scale, but there are important implications. A huge proportion of carbon dioxide emissions are absorbed by the oceans, both dissolving into the water and captured by planktonicplantlife. If animals swimming around are making a significant contribution to mixing up layers of the ocean this could be a major part of the climate equation that so far has been overlooked.

Oceanographer William Dewar writes an interesting commentary of this study in the same edition of Nature. He points how extraordinary it is that these processes acting at a tiny scale of mm and cm may have an affect on the vast oceans across hundreds of thousands of kms. Also, it is extraordinarily calm once you get down a short way into the oceans. All you would need is an electric kitchen hand-held mixer to stir up a cubic kilometer of sub-surface ocean. So, the jellyfish could be making a real difference down there.

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