Circulation in the Northern Japan Sea Studied Chiefly with Radiocarbon

Abstract

Radiocarbon concentrations in the northernmost region of the Japan Sea were observed during the summer of 2002. The averaged surface δ14C (above 100 m depth) was 52 ± 8%, which is significantly higher compared with the values of the Pacific Ocean and Okhotsk Sea. The δ14C in the deep water decreased with density, and the minimum value was −70%. By analyzing 14C and other hydrographic data, we found that i) the Tsushima Warm Current Water reaches to the surface layer in the southern Tatarskiy Strait; ii) deep convection did not occur in the northernmost region, at least not after the winter of 2001–2002; and iii) the bottom water that was previously formed in this region may step down southward along the bottom slope and mix with the Japan Sea Bottom Water. Furthermore, a new water mass characterized by high salinity (>34.09 psu) was found in the subsurface layer in the area north of 46°N.