Exploring Southern Ocean’s hidden drivers with direct numerical simulations

The Southern Ocean is critical in regulating the global climate by playing a key role in absorbing, transporting, and storing atmospheric carbon dioxide and heat. This is largely due to the region's unique geography, which connects multiple ocean basins and forms a complex network of global ocean circulation. This network spans a wide range of scales, from planetary motions to small-scale processes. Major large-scale features within its circulation network include the Antarctic Circumpolar Current, Slope Current, Subpolar Gyres, and Bottom Water formation, layered over finer processes like convection and turbulence. Conventional research into the Southern Ocean relies on Global and Regional Ocean and Climate Models which can incorporate realistic forcing like wind, topography and bathymetry. While these models are effective for large-scale motions, they struggle to resolve smaller-scale dynamics, leaving an incomplete picture of the region’s physical processes. To address this, Direct Numerical Simulations (DNS) are used to solve the fundamental equations of fluid dynamics within a small, idealized domain resembling the Antarctic region. This domain is driven solely by surface density variations and planetary rotation. By leveraging dynamic similarity, the small-scale results are scaled to represent the full ocean. This approach successfully captures all scales of motion and reveals the emergence of all major oceanographic features. Remarkably, the simulations show that convection alone can drive a cascade of interconnected physical processes, recreating the Southern Ocean's complex circulation without additional complexities like wind or bathymetry.