Subsurface kinetic energy source driven by Charney-type instability in oceanic fronts

Oceanic kinetic energy cascades regulate global climate, yet the mechanisms sustaining them beneath the mixed layer remain poorly constrained. Traditionally, the stratified ocean interior is viewed as quiescent, with submesoscale kinetic energy injection suppressed. Here we show that a distinct subsurface energy pathway is governed by Charney-type instability, converting available potential energy stored within subsurface fronts into kinetic energy in a rotating ocean. By integrating high-resolution observations with linear stability analysis, we identify that subsurface kinetic energy injection and transfer are decoupled from surface dynamics. Mechanistically, it acts as a “short-circuit” in the energy cascade: while primarily fueling inverse transfer, it simultaneously shunts ~10% of injected kinetic energy downscale, driving intense turbulent mixing comparable to surface wind forcing. Analysis of five global frontal systems indicates this mechanism is ubiquitous, with injection scales following the local Charney deformation radius. Our findings identify Charney-type instability as a self-sustaining engine of interior turbulence, bridging the gap between mesoscale eddies and microscale dissipation. Charney-type instability drives intense turbulent mixing in the ocean subsurface, according to high-resolution observations combined with linear stability analysis.