Recent upward shift of the deep convection system in the Japan Sea, as inferred from the geochemical tracers tritium, oxygen, and nutrients

Abstract

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.