Direct observation of the rapid turnover of the Japan Sea bottom water by means of AMS radiocarbon measurement

Increase of 14C in the bottom water of the Japan Sea for the last 16 years (1979–1995) was observed by means of AMS radiocarbon measurement. This increment is due to penetration of surface bomb radiocarbon, which obviously suggests a rapid turnover of the bottom water of the Japan Sea. The turnover time is estimated to be ca. 100 years which coincides with results obtained by other chemical tracers. By an application of the estimated turnover time to a box model of Δ14C change, pre‐bomb surface Δ14C in the northern Japan Sea where the bottom water is formed is calculated to be ca. −90‰.