The thermohaline circulation system in the Japan Sea, an almost land-locked marginal sea in the northwest Pacific, is now in a transition state. Comparison of vertical profiles of tritium, oxygen and nutrients between 1984 and 1998 demonstrates the following two points: (1) the supply of dense surface seawater to the bottom layer (>2,500 m in depth) has almost ceased since 1984, and (2) the intrusion of surface seawater to an intermediate depth range (between ~700 m and ~2,000 m in depth) has been reinforced during this 14-year period. Such transitional upward shift of the thermohaline conveyor belt in the Japan Sea is thought to have separeted the bottom water from the conveyor belt and brought about a stagnant mode of the bottom water. ¿ 2001 American Geophysical Union