Intensifying stratified turbulence and mixing towards the oceanic submesoscale front

The role of submesoscale processes as the primary energy source for ocean turbulence remains controversial due to observational limitations. Seismic imaging captures multi-scale processes from mesoscale to finescale, allowing us to infer turbulence processes. This study identified hundreds of ~200-m-long high seismic reflection patches, primarily caused by vertical temperature changes, moving at 0.24 ± 0.13 m/s across the deep-reaching front of Bransfield Current, Antarctica. Patch distribution within the main current is uneven, increasing exponentially towards the frontal leading edge. Over 95% of the detected patches are concentrated within 10 km from the frontal leading edge, where elevated Thorpe-scale diffusivity exceeding 10⁻² m²/s has been observed hydrographically. These patches may indicate stratified turbulence, including broken internal wave segments, interleaving interfaces, and overturns, which may correspond to wave breaking, frontal instability, and shear instability, respectively. Our findings challenge the recently questioned classical hypothesis that energy cascades directly from internal waves to isotropic turbulence, instead supporting the paradigm of a stratified turbulence stage.