In physical oceanography, a region in the Southern Ocean between the Southern ACC Front and the continent of Antarctica. It is characterised hydrographically by a water mass of uniform temperature and low salinity in the upper 500 m. The CZ is one of four distinct surface water mass regimes in the Southern Ocean, the others being (to the north) the Antarctic Zone (AZ), the Polar Front Zone (PFZ) and the Subantarctic Zone (SAZ).