for National Geographic News
Predicting global warming is far from an exact science, and it may have just gotten even more complicated.
Despite having been largely ignored by climate science, sea creatures' countless tentacle snaps, fin flaps, and tail twitches are responsible for a third or more of all "ocean mixing"—as much as winds or tides—according to a new study of jellyfish.
This mixing of seawater layers— and their salt, nutrients, carbon dioxide, and even heat—helps guide ocean circulation, which, like the atmosphere, moves heat around the planet.
If animal-driven ocean mixing is extensive and unaccounted for, as the new study argues, climate models—including those used to forecast global warming—may be off target.
Ocean in Motion
Some scientists argue that an animal such as a jellyfish is simply too small to create turbulence on a scale that could effectively mix layers of ocean water.
"You have to be stirring the fluid with a big-enough spoon to actually mix together waters of really different temperatures," explained Florida State University oceanographer William Dewar, who was not involved in the new study. Dewar comments on the debate in today's issue of the journal Nature.
But the study authors believe that even small swimmers stir the ocean in a big way, via a mechanism that Sir Charles Darwin, grandson of the legendary scientist, described half a century ago.
As an animal moves through the sea, it pulls some of the surrounding water along for the ride, explained Kakani Katija, a Ph.D. candidate in bioengineering at the California Institute of Technology.
Katija and colleagues witnessed this effect while diving with jellyfish in Palau's saltwater Jellyfish Lake, which is relatively protected from other mixing agents like wind and tides.
During dives in the lake, the team used turkey baster-like tools to squirt brightly colored dye along jellyfish's leading edges. As the jellyfish swam on, each took along an "aura" of the dyed water.
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