A 900-mile-long string of scientific instruments across a stretch of the open ocean has revealed the first evidence of giant internal waves partially "breaking" inside the oceans.

Tide-generated internal waves up to 300 feet tall are thought to mix shallow and deep waters when they break -- and so play a role in climate-critical ocean currents. Despite their size, they have been very hard to find in the act of fully breaking.

Like the surface waves that travel at the interface of water and air -- which have very different densities -- internal waves propagate deep down in the oceans where denser, colder and saltier deep waters meet warmer, fresher and less dense upper waters.

It's thought that internal waves play a big role in allowing cold, deep waters to well up to the surface in lower latitudes.

"The real key is not only how much turbulence, but where the turbulence is,"