Invisible Waves Shape Continental Slope, Researcher Says

Jun 30, 2008

A class of powerful, invisible waves hidden beneath the surface of the ocean can shape the underwater edges of continents and contribute to ocean mixing and climate, researchers from The University of Texas at Austin have found.

The scientists simulated ocean conditions in a laboratory aquarium and found that "internal waves" generate intense currents when traveling at the same angle as that of the continental slope. The continental slope is the region where the relatively shallow continental shelf slants down to meet the deep ocean floor.

They suspect that these intense currents, called boundary flows, lift sediments as the waves push into the continental slope, maintaining the angle of the slope through erosion. The action of the internal waves could also mix layers of colder and warmer water.

"Surprisingly little is known about how internal waves are generated and how they could lead to the mixing of the deep ocean, but it's very important," said physicist Hepeng Zhang. "Understanding ocean mixing is crucial for us to know whether changes in ocean circulation are the result of climate change or just variability."

Zhang said that as long as there is tidal motion that generates internal waves traveling along the continental slope, intense boundary flow will be produced.

"Twenty-four hours a day, seven days a week over a long geological time scale, and this will maintain the angle of the continental slope," he said.

He published his research with colleagues Harry Swinney and Benjamin King in Physical Review Letters.

Zhang studied internal waves using a simple saltwater aquarium equipped with a sloping bottom simulating the continental slope. Water in the tank increased in density from top to bottom, just as water is denser on the ocean floor. Thousands of very small particles, 10 microns or smaller, were suspended in the water.

As Zhang generated waves in the tank, he took photographs and video footage of the particles and then analyzed the particles' direction of flow and velocity.

Particle motion revealed intense boundary flows when the angle of the bottom matched the angle at which internal waves can travel.

Oceanic continental slopes could theoretically reach angles of 15 to 20 degrees as sediments continually pour down from the continents, but Zhang said that the internal waves are limiting the angle to around three degrees, the average angle of continental slopes.

The internal waves could also play a role in larger ocean currents by bringing cold water up from the deep ocean to the surface at the equator.

Ocean currents form closed loops, with warm surface water, like the Gulf Stream, moving toward the poles and cold water circulating back toward the equator at depth. The warm surface water heated at the equator is largely driven to the poles by wind. At the poles, this water is cooled by the cold air and mixes with cold water from melting glaciers and ice. Although fresh water is less dense than sea water, the cooling effect wins out and the density increases until the water sinks.

Zhang found that the internal waves could help bring this cold water closer to the surface when the boundary flow pushes 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.

"How exactly this will contribute to ocean circulation, I really don't know," said Zhang. "But it is definitely a step we have to understand before we can understand global ocean circulation."

Source: University of Texas at Austin

Explore further: New method for non-invasive prostate cancer screening

add to favorites email to friend print save as pdf

Related Stories

Heat wave offers glimpse into climate change

Aug 25, 2014

(Phys.org) —An unprecedented marine heat wave that swept the Southeast Indian Ocean in 2011 has given FIU scientists a glimpse into the future of climate change.

Climate change: meteorologists preparing for the worst

Aug 21, 2014

Intense aerial turbulence, ice storms and scorching heatwaves, huge ocean waves—the world's climate experts forecast apocalyptic weather over the coming decades at a conference in Montreal that ended Thursday.

The immediate aftermath of an oil spill

Aug 08, 2014

The fate of oil during the first day after an accidental oil spill is still poorly understood, with researchers often arriving on the scene only after several days. New findings from a field experiment carried ...

Recommended for you

New method for non-invasive prostate cancer screening

16 hours ago

Cancer screening is a critical approach for preventing cancer deaths because cases caught early are often more treatable. But while there are already existing ways to screen for different types of cancer, ...

How bubble studies benefit science and engineering

17 hours ago

The image above shows a perfect bubble imploding in weightlessness. This bubble, and many like it, are produced by the researchers from the École Polytechnique Fédérale de Lausanne in Switzerland. What ...

Famous Feynman lectures put online with free access

18 hours ago

(Phys.org) —Back in the early sixties, physicist Richard Feynman gave a series of lectures on physics to first year students at Caltech—those lectures were subsequently put into print and made into text ...

Single laser stops molecular tumbling motion instantly

22 hours ago

In the quantum world, making the simple atom behave is one thing, but making the more complex molecule behave is another story. Now Northwestern University scientists have figured out an elegant way to stop a molecule from ...

User comments : 0