From AMS Glossary
The water mass of the permanent or oceanic thermocline, which is located at a depth of between 150 and 800 m.
Central water is formed by subduction in the subtropics between 25° and 45° latitude in both hemispheres. It therefore spans a wide temperature and salinity range, with temperature and salinity both decreasing with depth. Each ocean has its own central water with its own specific temperature–salinity relationship depending on the atmospheric conditions in the formation region. These are distinguished by appropriate names, for example, South Atlantic Central Water, Western North Pacific Central Water, etc.