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The Antarctic Circumpolar Current Separates the cold polar oceans (density dominated by salinity) from the warm subtropical waters (density controlled by temperature). In the polar oceans cooling of the surface waters in autumn has little effect on the density of the mixed layer, allowing a rather thin surface layer to freeze to the freezing point before sea ice formation. Moving across the ACC, the cooling has a stronger affect on the density and causes convective deepening, eventually deepening the surface to depths that are so deep there is not enough winter sea-air heat loss to cool such a thick layer to the freezing point. There is a location where sea ice simply cannot grow because of this surface layer thickening—that location forming the virtual sea ice wall (SIW). This presentation discusses the underlying physics and shows the location of the SIW. Its climatological position aligns remarkably well with the climatological ice edge suggesting that the wall may actually be restricting the northern extent of the sea ice edge. Discussing the wall is preceded by a presentation of the Antarctic ocean-sea ice interaction, as well as a discussion comparing and contrasting such processes in the Arctic (mainly contrasting).