Southern Ocean polar cyclones drive extreme atmospheric anomalies over Antarctic sea ice

High-latitude cyclones in the Southern Ocean can reach and shape the Antarctic sea-ice. Rare in-situ measurements from a winter cyclone in the marginal ice zone evidence how it caused both significant wave activity and large atmospheric temperature and moisture anomalies. We investigate here with the help of reanalysis data, whether cyclones may routinely lead to the presence of unusually warm, moist air masses over ice-covered regions in the Southern Ocean. We find that extreme atmospheric anomalies over sea ice often occur in the absence of cyclones, and that intense cyclones have a stronger association with extreme temperature anomalies than extreme moisture anomalies. This points to a nuanced link between high-latitude Southern Ocean cyclones and atmospheric anomalies over Antarctic sea ice.  We next consider whether cyclones may also lead to variability in winter Antarctic sea-ice concentration. We characterise sea-ice variability and cyclone activity in different Southern Ocean sectors using atmospheric reanalyses and a cyclone-tracking algorithm, and then quantify the proportion of extreme sea-ice variability engendered by cyclones of different intensity. We conclude that there is a significant link between variability in winter sea-ice concentration and: (1) all cyclones in the Ross/Amundsen sector; (2) all but the weakest cyclones in the King Haakon VII, East Antarctic, and Bellinghausen sectors; and (3) all but the most intense cyclones in the Weddell sector. More generally, up to 40% of episodes of extreme sea-ice variability are caused by extratropical cyclones within all regions apart from the Weddell sector, (where extreme sea-ice variability is less connected to the fewer intense cyclones and more to the weaker cyclones).