Subsurface Ocean Waves Can Be More Than 500 Meters High

An anonymous reader writes: New field studies out of MIT found that "internal waves" — massive waves below the surface of the ocean — can reach enormous sizes. The most powerful internal waves known to science are in the South China Sea, and they can be over 500 meters high. These waves mix disparate layers of ocean water, and contribute to evening temperatures between various bodies of water (abstract). The waves grow larger as they propagate, and carry on all year. These waves have enough mass to affect the earth-moon system: "To cut a long story short, it's not unreasonable to say internal waves play a role in the moon moving away or receding from the Earth. They are big enough that they affect large-scale celestial motions."

Comments

Amplitude not Height

[Roger W Moore]

I think you mean that their amplitude can be as much as 500m. For a start these are not surface waves so they do not raise the water surface. Additionally, although the article does not really specify it, I would expect that they are actually far more longitudinal than transverse in nature and so the displacement will be almost entirely in the same direction of the wave motion i.e. horizontal. Fluids generally tend to be very poor transmitters of transverse waves because they cannot support a shear stress.

Re:Effect on life?

[Obfuscant]

Well, considering that they only exist because of a difference in density between the upper and lower layers involved, the massive movement of colder/saltier/etc water will have a definite impact on what lives in that water.

"Internal waves" are no different than (i.e. obey the same scientific principles as) surface waves. They are both "interfacial waves". The difference is that the air/water density difference is much greater than the water/water density difference.

It has an impact on land-based life as it can drive upwelling, which both causes cooler temperatures near the shore and provides nutrients for sea life.

Re:Aren't they called Currents?

[bruce_the_loon]

They are not currents because the water isn't flowing, it is moving in place, albeit a 500m range.

Waves in all definitions are movements within a fluid where the particles move back and forward around a fixed point. The dictionary definition is inaccurate by stating that the disturbance is at the surface, the movement happens through the body of water. It is visible at the surface, but it takes place in the body.