In physical oceanography, the name given to a transition region in the Southern Ocean (SO) or Antarctic Circumpolar Current (ACC) between the Subantarctic Front (SAF) to the north and the Polar Front (PF) to the south. This was first called the Antarctic Polar Front Zone in the mid–1970s but later modified to the present name. It is identified as a region bound between the 3–9° C surface isotherms. The PFZ is one of four distinct surface water mass regimes in the Southern Ocean, the others being the Subantarctic Zone (SAZ) to the north and the Antarctic Zone (AZ) and Continental Zone (CZ) to the south.