Woods Hole Oceanographic Institution

Round and round it goes
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Food dyes added to water on a rotating table represent water from different depths, to model how vortices form around seamounts. (Photo by Tom Kleindinst, WHOI Graphics Services)
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Physical Oceanographer Claudia Cenedese, left, with Rachel Bueno de Mesquita. (Photo by Tom Kleindinst, WHOI Graphics Services)

At first glance, it looks like an art project: a spinning Plexiglas box filled with paint. To Claudia Cenedese, the box contains the ocean—but on a miniature scale.

A plastic mound in the center of the box represents a seamount—an extinct submarine volcano—that would span 1,500 kilometers (930 miles) in the real ocean. Colored food dyes are injected into the water from different locations on the “seamount” (blue from the bottom, red from the middle, and green from the top). The table rotates as the Earth does. A camera above, rotating in synchrony with the table, photographs the swirling field of small vortices that spin off the seamount. One large, single vortex (green), however, forms above the seamount.

The same basic physical laws that govern geophysical fluid dynamics in the box apply in the real ocean. In this experiment, Cenedese (in blue, at right), an associate scientist in the Physical Oceanography Department, and Rachel Bueno de Mesquita, a visiting undergraduate from the University of Rome, explore how seamounts sticking up from the seafloor modify ocean circulation and create organized, rather than random, patterns of vorticity. Such experiments reveal subtle complexities of ocean circulation. They also help explain, for example, how larvae of animals living on seamounts might spin out to colonize new seafloor regions (as indicated by blue or purple dyes), or alternatively, spin endlessly around the seamount and become trapped in one region (as indicated by the green dye).

Theoreticians create mathematical equations with all the interacting variables that go into complex geophysical fluid dynamics. Observationalists go to sea to observe actual ocean dynamics, but can observe only a tiny portion of a wide-scale process. Somewhere in between is Cenedese, an experimentalist, who devises laboratory studies to observe and measure actual fluid dynamics on a small scale.

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