Jellyfish Are the Dark Energy of the Oceans?

The fluid dynamics of swimming jellyfish have provided a plausible mechanism for a once-wild notion: that marine animals, hidden from sight and ignored by geophysicists, may stir Earth’s oceans with as much force as its wind and tides.

Called induced fluid drift, it involves the tendency of liquid to “stick” to a body as it moves through water — and a little bit of drift could add up quickly on a global scale.

The idea that animals could play a profound role in water-column commingling was once considered absurd, but in recent years, this consensus has sprung some leaks. When added up, winds and tides don’t quite provide enough energy to account for the amount of water-mixing observed in the seas.

In 2004, a study found that a school of fish could cause as much turbulence as a storm. Other researchers soon suggested that ocean swimmers could account for the gap. Soon after that, ocean physicists measured enormous turbulence generated by a swarm of krill, a crustacean considered too small to have meaningful mixing effects.

One physical explanation for how tiny forces could avoid being swallowed by the friction of the sea was that the act of swimming created pressure differentials that pulled water along with a body.

Scientists have provided the first direct observation of this phenomenon. Using fluorescent dyes and underwater video cameras, they’ve made visible the invisible, producing videos of swimming jellyfish trailed by the water they came from.

If the video seems like an infinitesimal drop in the bucket compared to winds or tides, consider that most of the ocean — excepting the top 300 feet or so — is so placid that a couple hand-held kitchen mixers could stir a cubic mile of it.

Scientists believe induced fluid drift could be caused by any swimming animal. Their next task is to verify that it does, and to put numbers to how much water is moved by each animal, how it mixes, how the figures vary by body shape and size and population density.

Original article here.