The ocean is like a layered cake: warm, light water on top, cold, heavy water below. Between the layers, at the interface, invisible waves roam. They don't lift crests like a storm; instead, they slowly rock the entire water column, as if someone were shaking a giant aquarium from within. These internal waves carry energy and heat, mix nutrients, and influence the planet's climate.

Scientists have long noticed that if you measure the strength of internal waves at different depths and frequencies, you get the same picture — in any ocean, at any time of year. This universal pattern is called the Garrett–Munk spectrum. But where it comes from remained a mystery for a long time. In the new work, researchers derived this spectrum directly from the equations of water motion — the very ones that describe how fluid flows and rotates with the Earth.

The key step was accounting for the Earth's rotation. Previously, it was discarded to simplify calculations, but it is precisely what makes the waves stable and prevents energy from accumulating in one place. It turned out that the distribution of energy across depths and frequencies can be obtained without fitting formulas to data, simply by following the laws of physics. Moreover, energy flows from large waves to small ones, like water spreading through capillaries.

This result is like a map that allows predicting where heat moves in the ocean. And that means better understanding how the ocean breathes and how it will respond to climate change.