The Antarctic Convergence, also known as the Antarctic Polar Frontal Zone, is a line encircling Antarctica where the cold, northward-flowing Antarctic waters sink beneath the relatively warmer waters of the sub-Antarctic. The line is actually a zone approximately 20 to 30 miles wide, varying somewhat in latitude in different longitudes, extending across the Atlantic, Pacific, and Indian Oceans between the 48th and 61st parallels of south latitude. The precise location at any given place and time is made evident by the sudden change in surface temperature, which averages 5 to 10 degrees Fahrenheit (2.8° C to 5.5° C).