Submesoscale Stirring Drives Lateral Dispersion and Vertical Exchange in a Cyclonic Mesoscale Eddy

Abstract Identifying and quantifying submesoscale stirring in the ocean remains a significant challenge. This study investigates the lateral dispersion and vertical transport effects within a cyclonic mesoscale eddy, using a combination of submesoscale‐permitting in situ observations and model data. By analyzing water mass variations along cross‐eddy isopycnals, distinct dispersion behaviors are identified at different depth layers. The analysis reveals an equivalent submesoscale along‐isopycnal diffusivity larger than 100 m 2 s −1 in the eddy's subsurface layer. To further examine transport pathways, Lagrangian particle tracking experiments are conducted using LLC4320 model output, presenting the features of lateral spreading and vertical penetration at various depths and locations within the eddy. Our results show that in the mixed layer, submesoscale stirring associated with submesoscale instabilities drives efficient lateral dispersion away from the eddy core. While in the subsurface stratified layer, internal wave motions significantly enhance vertical shear, which drives isopycnal submesoscale stirring. This process disrupts the eddy's coherence and causes vertical tracer exchange. These findings emphasize the essential role of submesoscale stirring processes in driving both lateral and vertical tracer dispersion and consequently affecting the eddies' capacity to trap water masses.