Impacts of ocean mixing on the Winter Mixed Layer under Sea Ice in the Weddell Sea: Insights from a Large Eddy Simulation

Sea ice form a dynamic interface between the ocean and atmosphere in polar regions, significantly influencing global climate patterns and marine ecosystems. Winter-mixed layers under sea ice in the Southern Ocean (SO) undergo complex interactions between the atmosphere and the ocean. During the ice formation months (June-September), brine rejection and near-freezing surface temperature make the water column relatively weakly stratified as warm and saline deep water sits right under the cold, fresh, mixed layer (ML) and is susceptible to convective instabilities. We have conducted convection resolving large eddy simulation (LES) to model the ML growth during the winter and characterize the mixing. LES results are compared with observational data and agree well with the ML properties. The results show the rapid deepening of ML during the earlier phase of winter due to high conductive heat flux through thin sea ice, which assists faster sea-ice growth that triggers a high rate of ML deepening owing to large brine rejection. The later stage leads to a slower rate of sea ice formation by reduced conductive heat flux resulting in slower ML deepening. Simulation shows that fine-scale turbulent eddies are crucial in redistributing heat and salt within the ML during sea-ice formation phases and play a vital role in ML dynamics and sea-ice growth. The data from the present study will also indicate improvements required in the parameterization used in large-scale ocean and climate models for the SO.