Circulation in the northern Japan sea studied chiefly with radiocarbon

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.