Turbulent mixing in the deep ocean interior runs at roughly one ten-thousandth of a watt per kilogram — a vanishingly small dissipation rate that nonetheless drives the global overturning circulation. Without it, the dense water that sinks at high latitudes would simply pool at the bottom and stay there. The ocean would stratify into a cold abyss capped by a warm lid, and the conveyor that redistributes heat across the planet would stall. The question has always been where the energy comes from.

The answer is internal waves — oscillations that propagate along density gradients within the water column, generated predominantly by winds and tides. These waves do not break at the surface like their more familiar cousins. They break internally, transferring energy from large-scale oscillations to turbulence through nonlinear interactions that cascade energy downscale until the waves become unstable, overturn, and mix the surrounding water. Dematteis and colleagues applied wave-interaction theory — developed originally for surface gravity waves — to the ocean interior and found near-ubiquitous agreement between first-principle predictions and observed mixing patterns across the global ocean.

The result is striking not for its novelty but for its completeness. The theory requires no tunable parameters fitted to local observations. It takes only the measured internal wave spectrum as input and predicts the mixing rate as output. The physics is the same everywhere — only the wave energy varies.

The through-claim extends beyond oceanography. Any stratified medium where waves propagate along density interfaces — the atmosphere, stellar interiors, magma chambers — faces the same physics. Energy enters at large scales, cascades through nonlinear wave interactions, and dissipates through local breaking events. The breaking is invisible from outside. The mixing it produces determines the large-scale structure of the entire system.