Southern Ocean Sea Ice-Ocean Interactions in a Simple Box Model

Subsurface warming has been identified as a likely causal factor for the sustained low Southern Ocean sea ice extent in recent years. Subsurface-to-surface heat transport is impacted by the water mass structure of the water column and the depth of vertical mixing, which can in turn be altered by sea ice processes. These interactions create potential feedback effects that remain insufficiently explored in the context of the recent low Southern Ocean sea ice extent. In this study, we investigate interaction mechanisms and feedbacks between Southern Ocean sea ice and the underlying water column through a simple one-column box model, focusing on water mass structure and properties. The model represents the surface mixed layer, subsurface Winter Water, and the Upper Circumpolar Deep Water as distinct ocean boxes. A fourth box represents sea ice when present, interacting with the mixed layer through heat and salt exchange. The evolving mixed layer depth is calculated using a mixed layer model, with subsurface Winter Water formed when the mixed layer shoals and re-entrained when the mixed layer deepens. In this contribution, we present the box model framework and discuss preliminary insights, as well as challenges encountered during the model development process.