THE Southern Ocean is the only oceanic domain encircling the globe. It contains the strong eastward flow of the Antarctic Circumpolar Current, and is the unifying link for exchanges of water masses at all depths between the world's major ocean basins1. As these exchanges are an important control on mean global climate, the Southern Ocean is expected to play an important role in transmitting climate anomalies around the globe. Interannual variability has been often observed at high southern latitudes, and observations of sea-ice extent suggest that such features propagate eastwards around the Southern Ocean2,3. Here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level, wind stress, sea surface temperature and sea-ice extent over the Southern Ocean. These anomalies propagate eastward with the circumpolar flow, with a period of 4-5 years and taking 8-10 years to encircle the pole. This system of coupled anomalies, which we call the Antarctic Circumpolar Wave, is likely to play an important role in climate regulation and dynamics both within and beyond the Southern Ocean.