A high-resolution, submesoscale-resolving ocean model of South East Queensland (ROMS v4.2)

Abstract. The ocean exhibits a continuum of motions spanning basin-scale circulation to micro-scale turbulence where between mesoscale eddies and small-scale turbulence lies the submesoscale (∼0.1–10 km, hours-days). The submesoscale is characterised by fronts, filaments and small coherent vortices that arise from instabilities of mesoscale currents, interactions with topography, and buoyancy forcing. These processes restratify the upper ocean while simultaneously enhancing vertical tracer exchange through intense vertical velocities concentrated at density gradients. In the East Australian Current, the western boundary current of the South Pacific Gyre, the jet accelerates and interacts with the continental shelf off South East Queensland, creating conditions favourable for submesoscale activity. Yet these processes remain unresolved and unexplored in existing regional simulations: mesoscale regional models do not resolve energetic frontal processes, high-resolution coastal models lack realistic offshore forcing, and observations alone are insufficient to constrain the three-dimensional subsurface circulation. Here, we present a submesoscale-permitting implementation of the Regional Ocean Modelling System (ROMS v4.2) for the EAC jet intensification region offshore of South East Queensland and northern New South Wales, Australia. We demonstrate that our model generates energetic fronts and filaments along the continental shelf edge, while maintaining surface and subsurface mesoscale hydrographic structure consistent with observations. Relative to mesoscale-resolving simulations, the configuration exhibits substantially increased hotspots of divergence, vorticity and vertical velocity variance, together with a flatter kinetic energy spectrum indicative of resolved submesoscale dynamics. A demonstration of the continental shelf break in the vicinity of K'gari shows the accelerating jet interacting with coastal promontories and the shelf break, producing localised and persistent submesoscale activity. This configuration enables investigation of submesoscale emergence and interaction with the mesoscale circulation, including jet-shelf modification, cross-shelf exchange and energy transfer across scales. This approach provides a pathway to quantify energy pathways and ocean dynamics, with applications extending beyond the East Australian Current to other western boundary current systems.