The amount of water moved, of course, varies with an animal's size and shape. But the distance an animal travels is also a factor.
"The drifting fluid essentially stretches along the length of the migration, so if an animal migrates 500 meters [1,600 feet], that [water] will move 500 meters," explained Katija, who co-authored the new study, which appears in today's issue of Nature.
And though jellyfish don't cross seas like finned animals, in a single day the spineless beasts often ascend and descend hundreds of yards, migrating through multiple ocean layers.
Stirring It Up
While seas may seem turbulent on the surface, deep below they're surprisingly calm—and can be mixed by even small-scale disturbances.
In the subsurface ocean, for example, a typical handled mixer "would provide enough energy to mix a cubic kilometer [about 264,200 gallons] of ocean," Florida State's Dewar said.
Needless to say, "if a giant squid swims through, you've got a significant bit of mixing right there."
But research scientist André Visser countered that the seas are "quite a thin soup of organisms"—there might not be enough animals to create significant global mixing.
"Organisms can mix the water, that's true," said Visser, of the Technical University of Denmark. "We know that dense assemblages of swimming fish or of bivalves pumping water on the sea bed can have large effects on local conditions.
"But the question is, do they have impact on a global scale that can [influence] climate? That's where the whole story becomes a bit fuzzy."
Study co-author Katija said she's confident that the mechanism works on a global scale. But even she has questions about just how swimming animals affect the ocean.
"For example, what happens if you have a huge population, or school, of animals that are moving in concert?" she said. "Do you perhaps treat that whole population as a body itself?"
Also blurry are the effects of different swimming styles on water transport: a shark's vigorous tail thrusts, say, versus a jellyfish's slow-motion undulations. Even the countless things that sink passively to the ocean floor, like fish droppings, could conceivably help to mix the waters.
For now, the concept is highlighting just how much we don't know about ocean mixing and how it affects our climate, both present and future.
"I think it's really quite important work, because at the moment nobody accounts for any biological feedback in climate models," Florida State's Dewar said. "I think this paper will cause people to think about it a lot more."
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