A water mass in the Japan Sea that comprises all the water below 200 m (and thus the overlying Japan Sea Middle Water). It is characterised by uniform temperature (1- 2° C) and salinity (34.1) which result from its isolation from other basins by shallow sills. It is formed via winter convection facilitated by the salt imported by the Tsushima Current, with the instabilities in the Polar Front serving to transport this salt into the northern formation regions. Some authors differentiate Japan Sea Deep Water (JSDW) (200 - 2000 m) and Japan Sea Bottom Water (JSBW) (2000 m - bottom), and occasionally the entire water mass is referred to as Japan Sea Deep Water.