Sea level is a key indicator of ocean change, but it is hard to measure around Antarctica, where sea ice hides the ocean from satellites. Yet satellites flying over the ice still receive clear echoes from openings in the ice, where water is exposed. We reprocessed these echoes from four satellite missions and combined them with open-water data, building the longest sea level record for the whole Southern Ocean (2003 to 2021). It offers a new way to track how this rapidly changing region evolves.