Spatial distribution of radiocarbon in the southwestern Japan/East Sea right after the bottom water renewal

Abstract

The Japan/East Sea, which has a maximum depth of more than 3700 m, is a marginal sea separated from the western North Pacificby the Japanese Islands and Sakhalin. Because of its shallow sill depths (<140 m), the deep water in the Japan/East Sea, which iscalled the Japan Sea Proper Water (JSPW), is formed within the Sea itself. JSPW consists of two waters of the bottom water (lowerlayer of JSPW) and the deep water (above the bottom water). The bottom water is characterized by extremely homogeneous in thevertical distribution of temperature and chemical variables of seawater such as dissolved oxygen. The origin of the water is thesurface water in the northern Japan/East Sea, because the surface water in winter due to evaporation and/or freezing at the seasurface is dense enough to sink toward the bottom. Therefore, the bottom water is colder and richer in dissolved oxygen than thedeep water in the North Pacific. The dissolved oxygen in the bottom water, however, has been decreasing since the 1960’s or earlierto the present, probably due to the reduced deep convection in the sea during the recent global warming. On the other hand, newlyformed bottom water was found in the northwestern Japan/East Sea in the summer of 2001 after the severe winter 2000&#8211;2001. Thenew bottom water showed low temperature, high salinity and high dissolved oxygen compared to the old bottom water. n/East Sea, which iscalled the Japan Sea Proper Water (JSPW), is formed within the Sea itself. JSPW consists of two waters of the bottom water (lowerlayer of JSPW) and the deep water (above the bottom water). The bottom water is characterized by extremely homogeneous in thevertical distribution of temperature and chemical variables of seawater such as dissolved oxygen. The origin of the water is thesurface water in the northern Japan/East Sea, because the surface water in winter due to evaporation and/or freezing at the seasurface is de