Anomalous distribution of dissolved organic carbon in the Sea of Japan

Dissolved organic carbon (DOC) in the Sea of Japan was determined by the high temperature catalytic oxidation (HTCO) method. The chemical parameters related to DOC, i.e., the three-dimensional excitation-emission matrix spectrum, nutrients, chlorophyll a, dissolved oxygen and monosaccharides concentration were also determined. The vertical distribution of DOC in the northernmost sampling site (CM10; 44.1°N, 138.6°E) was not like that those in other sampling sites. An anomalously high DOC concentration was observed for the middle layer (250 to 1000 m) at CM10, which was two or three times higher than the concentration for the same layer at other sampling sites. Moreover, dissolved oxygen, nutrients and fluorescence intensity of marine humic-like substances were also unusual for the middle layer of CM10, compared to the same layer at other sampling sites. The amounts of Chl. a and monosaccharides between the surface and 100 m depth at CM10 were larger than those of other sampling sites. In the middle layer, the water mass structure of CM10 differed from that of other sampling sites. These results suggested that the cause of the DOC distribution anomaly at CM10 could be considered as due to the inflow of quite different water mass with incomplete oxidation of organic matter.