Hobbs, W. R.Holmes, RyanKiss, Andrew E.2026-02-122026-02-122169-9275https://hdl.handle.net/1885/733805464Winter Antarctic sea ice extent has historically shown relatively low variability compared to warmer seasons, but recent winters have shown very extreme low ice cover. As a result, there is significant interest in understanding the physical constraints on winter Antarctic sea ice cover. In this work the ocean's role in constraining maximum extent is explored. Using basic physical principles, the concept of “Stability at Freezing Temperature” is introduced, and then applied to calculate the total ocean heat that must be lost to the atmosphere before sea ice can begin to form. This method is found to capture spatial and interannual variability of the winter sea ice edge, including during recent extreme sea ice cover states. This framework can be used to separate the effects of ocean thermal and haline anomalies on the ice edge. It is also used to quantify the contributions from summer preconditioning, atmospheric cooling, and subsurface ocean heat transport, all of which are shown to contribute significantly to winter ice extent variability. This method provides an invaluable tool for understanding recent sudden changes in Antarctic sea ice cover.This project received Grant funding from the Australian Government as part of the Antarctic Science Collaboration Initiative program, and the Australian Research Council (ARC) Discovery Project DP 230102994, ARC Discovery Early Career Researcher Award (DE21010004) and ARC Linkage Project LP200100406. This work was supported by computational resources provided by the Australian Government through the National Computational Infrastructure (NCI) under the National Computational Merit Allocation Scheme and ANU Merit Allocation Scheme. We thank the Consortium for Ocean–Sea Ice Modeling in Australia (COSIMA; cosima.org.au) for making the ACCESS-OM2 models, outputs and analysis tools available through the NCI. Open access publishing facilitated by University of Tasmania, as part of the Wiley - University of Tasmania agreement via the Council of Australian University Librarians.14en© 2026. The Author(s).Antarcticpolarsea ice202610.1029/2025JC022716105028405103