ABSTRACT

Analyses of 106 surface samples of the sediment on the floor of the Japan Sea were made for color, grain size, calcium carbonate, organic carbon, and mineralogy. The results showed that the sediments on the shelves and bank tops are largely coarse-grained green moderately calcareous sands having less than 1 percent organic carbon. Those on the basin slopes are fine-grained green (grading to olive brown below about 1800 m depth) slightly calcareous silts having 1 to 2 percent organic carbon. Below about 2000 m and covering the flat floor of the sea is yellow-brown clayey silt containing less than 1 percent calcium carbonate and less than 1 percent organic carbon. This deepest sediment approaches the character of red clay that occurs in the open ocean chiefly at depths of more than abou 3000 m. Its relatively shallow occurrence in the Japan Sea is attributed to the presence of an exceptionally high content of dissolved oxygen (about 5.3 ml/l) in the bottom waters of the sea. Their high oxygen content is due to sinking of surface waters at the north end of the sea during wintertime cooling.