They may not look as though they can make waves, but new research has found that the collective swimming motion of brine shrimp (Artemia salina) and other zooplankton can generate enough swirling flow to potentially influence the circulation of water in oceans.
The study by researchers at Caltech found the effect could be as strong as those due to the wind and tides, the main factors that are known to drive the up-and-down mixing of oceans.
The behaviour of brine shrimp is cued by light: at night, they swim toward the surface to munch on photosynthesising algae while avoiding predators. During the day, they sink back into the dark depths of the water.
To study this behaviour in the laboratory, researchers used a combination of blue and green lasers to induce the shrimp to migrate upward inside a big tank of water. The green laser at the top of the tank provided a bright target for the shrimp to swim toward while a blue laser rising along the side of the tank lit up a path to guide them upward.
The tank water was filled with tiny, silver-coated hollow glass spheres 13 microns wide (about one-half of one-thousandth of an inch). By tracking the motion of those spheres with a high-speed camera and a red laser that was invisible to the organisms, the researchers measured how the shrimp's swimming caused the surrounding water to swirl.
Adding up the effect of all of the zooplankton in the ocean — assuming they have a similar influence — could inject as much as a trillion watts of power into the oceans to drive global circulation, says John Dabiri, professor of aeronautics and bioengineering at Caltech. In comparison, the winds and tides contribute a combined two trillion watts.
The researchers describe their findings in the journal Physics of Fluids.
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