 "Photo: Buddy Burkhalter")
Below the surface of the ocean, strong waves shape the continental slope and contribute to climate changes. UT researchers have constructed a saltwater tank to simulate these "internal waves" along the ocean floor. Sand-grain-sized particles in the water allow the researchers to follow the water's movement using video cameras.
"We literally use a fish tank," said graduate researcher Benjamin King. "In the ocean, you might know the velocity of the water every few miles. In the lab we can figure out the velocity at every square centimeter."
The researchers found that internal waves, which can travel for hundreds of thousands of miles under the ocean's surface, alter the angle of the continental slope, which is the region where the ocean floor drops off rapidly from the continental shelf.
Physics professor Harry Swinney, postdoctoral fellow Hepeng Zhang and King published their research in the scientific journal "Physical Review Letters" on June 20.
"The question we've addressed is what causes [the continental slope] to drop off at an angle of 3 or 4 degrees rather than an angle of 20 or 25 degrees. It seems there is nothing that would prevent a steeper fall off," Swinney said.
In theory, erosion from landmasses should cause the continental slope to be much steeper than their observed gradients, King said. The internal waves can be generated by the continental slope itself, and those same waves help to modify the slope's shape.
"Internal waves are very unusual waves because they only travel at a certain angle," Swinney said.
As sediments build up along the continental slope, the slope reaches a critical angle at which it becomes very efficient at generating internal waves, which then maintain the angle of the slope, King said.
Although the research focuses on the effects of internal waves on the continental slope, the researchers said internal waves also contribute to ocean mixing, which affects the movement of ocean currents and, in turn, climate change.
King explained how observation of global ocean circulation allows scientists to conclude that there must be mixing in the deep ocean, which can be caused by internal waves.
"Internal waves, when they break, cause a lot of turbulence and mixing in the deep sea … that helps sustain the global ocean circulation we observe," King said.
Ocean mixing, caused by internal waves, could result in dramatic climate change.
"Currently, the Gulf Stream that carries warmer equatorial waters to northern Europe makes the land mass warmer. If that current were to somehow stop, that could change the climate there," King said.
It is possible to measure internal waves in the ocean using buoys and censors, but, he said, this is expensive, and the data collected is sparse.
"What we learn from the experiment will be generally useful in understanding flows on any planet," Swinney said.
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