July 29, 2009

Underwater Animals’ Role In Ocean Water Stirring

Underwater creatures, including small swimming animals like jellyfish, play a crucial role in the mixing of ocean waters, scientists reported on Wednesday.

Writing in the July 30 issue of the journal Nature, John Dabiri, a Caltech bioengineer and Caltech graduate student Kakani Katija, discovered that both large and small underwater creatures contribute to the process of ocean mixing.

"The perspective we usually take is how the ocean--by its currents, temperature, and chemistry--is affecting animals," said Dabiri.

"But there have been increasing suggestions that the inverse is also important, how the animals themselves, via swimming, might impact the ocean environment."

Ocean mixing is the process by which water is stirred to distribute heat, nutrients and gasses throughout the ocean.

Scientists had previously believed that animals did not play a large role in the processes which allowed ocean mixing to occur.

During the mid-19th century, evolutionary theorist Charles Darwin put forth the idea that small underwater fish and other animals collectively played a key role in the mixing of ocean waters.

"Darwin's grandson discovered a mechanism for mixing similar in principle to the idea of drafting in aerodynamics," Dabiri explains. "In this mechanism, an individual organism literally drags the surrounding water with it as it goes."

Modern scientists have passed this notion off, claiming that there was no evidence to support such a claim.

However, Dabiri and Katija used mathematical models to show what would happen if underwater animals were to swim in the same direction simultaneously.

They found that the water's viscosity gave credence to Darwin's theory for ocean mixing through small creatures.

They found that oceanic creatures are able to carry water from the lower portions of the ocean to the upper regions by traveling upward.

"It's like a human swimming through honey," Dabiri said. "What happens is that even more fluid ends up being carried by a copepod, relatively speaking, than would be carried by a whale."

"There are enough of these animals in the ocean," Dabiri said, "that the global power input from this process is as much as a trillion watts of energy, comparable to that of wind forcing and tidal forcing."

"This may have an impact on carbon sequestration on the ocean floor," Dabiri added. "It's something we need to look at."

"Results from this study will change some of our long-held conceptions about mixing processes in the oceans," says David Garrison, director of NSF's biological oceanography program, which funded the research.


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