SPATIAL DISTRIBUTION OF RADIOCARBON IN THE SOUTHWESTERN JAPAN/EAST SEA IMMEDIATELY AFTER BOTTOM WATER RENEWAL

Abstract

In April 2001, immediately after bottom water renewal in the Japan/East Sea, 7 vertical profiles of radiocarbon were obtained from the area, including the Japan Basin and the Tsushima/Ulleung Basin. The bottom water Delta C-14 of the Tsushima/Ulleung Basin increased by 24% during 1979-2001 and was 10-15% higher than the values reported for the Japan Basin and Yamato Basin during 1995-2002. Within the depth interval 800-2000 m, Delta C-14 values at the southernmost station in the Japan Basin were much higher than at other stations, with the maximum difference in Delta C-14 values being more than 50%. Based on a combination of physical observations with analysis of the Delta C-14 data, we concluded that the bottom water, which was formed by the sinking of surface water off Vladivostok, Russia, in late January-early February of 2001, had been widely distributed to depths below 2000 m within the southernmost Japan Basin in a timespan shorter than 2 months. However, there was no evidence that the water had been transported into the Tsushima/Ulleung Basin during the same time interval.