Quasi-universal high-frequency kinetic energy spectrum in the surface mixed layer

High-frequency motions in the ocean surface mixed layer are traditionally considered distinct from internal-wave dynamics in the ocean interior. Using global surface drifter observations, we show that the high-frequency kinetic energy (HFKE) spectrum in the mixed layer exhibits a robust, quasi-universal form that closely resembles the classical Garrett–Munk internal-wave spectrum, despite the latter being formulated for the stratified ocean interior. This unexpected resemblance persists across diverse dynamical regimes. Further analysis reveals that mesoscale eddies primarily regulate spectral slopes, while near-inertial waves modulate energy levels. These results suggest a universal scaling in HFKE spectra and offer new insights into upper-ocean dynamics.