The water mass of the permanent or oceanic thermocline (100–600 m) in the tropical Pacific from 20°S to 15°N. South Pacific Equatorial Water (SPEW) occupies the region south of the equator; it is derived from central water and an injection of high-salinity water formed by evaporation near Polynesia that sinks to a depth of 200 m. North Pacific Equatorial Water (NPEW) is found north of the equator; it is formed by subsurface mixing between SPEW and central water. Indian Central Water is a historical term used for Australasian Mediterranean Water in the western Indian Ocean before the Indonesian Seas were recognized as its source region.