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Invisible Waves

Invisible Waves
This video still of particles suspended in water shows how internals waves can billow and mix water along the continental slope.
This video still of particles suspended in water shows how internals waves can billow and mix water along the continental slope.


Hidden beneath the surface of the sea, powerful “internal” waves are shaping the underwater edges of continents and contributing to ocean mixing and climate.

Physicists Hepeng Zhang and Harry Swinney simulated such waves using a simple saltwater aquarium equipped with an angled bottom simulating a continental slope (the region where the shallow continental shelf slants down to meet the deep ocean floor). As Zhang generated waves in the tank, he took photographs and video footage of thousands of very small particles, 10 microns or smaller, suspended in the saltwater, and then analyzed the particles’ direction of flow and velocity.

He discovered that internal waves erode continental slopes and limit their angle to around three degrees. He also found that internal waves could help bring cold water from the deep ocean closer to the surface by pushing heavier, colder water over warmer lighter water on the continental slope. This results in the internal wave breaking and mixing on the slope, just as a surface wave breaks on the shore (pictured above).

Understanding internal wave action is important, says Zhang, because the waves could lead to mixing of the deep ocean. “Understanding ocean mixing is crucial for us to know whether changes in ocean circulation are the result of climate change or just variability,” he says.

This article also appeared in the Spring 2009 issue of Focus magazine.
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Thursday, 16 July 2020

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