Abstract
The distributions of nutrients, chlorophyll, and particulate matter in the Seto Inland Sea have been investigated by two extensive surveys in August of 2002 and 2003. To establish the basis for stoichiometric analysis in the Seto Inland Sea, the spatial distributions of nutrient ratios were analyzed. The results along a central section in the summer regime showed a highly differentiated pattern of vertical structure, which was caused by the inhomogeneous distribution of tidal mixing. Among straits which were strongly mixed, biogeochemical properties were vertically distributed homogeneously. On the other hand, in most quiescent basins, nitrate and phosphate pools were formed on the bottom, and chlorophyll maxima were formed in subsurface layers. The concentration of dissolved silicate was high from the bottom to the surface in the region between 133.2°E~134.4°E. The concentration of nitrite (NO2-N), which was generated in the process of nitrification or denitrification, was higher than that of nitrate (NO3-N) in eastern Harima-Nada, the Akashi Strait and western Osaka Bay. High nutrient concentrations corresponding to a cold pool were observed in the lower layer of the Bungo Channel and the Kii Channel. The comparisons of the DIN /DIP and DSi/DIN ratios between those regions and the open ocean indicates that the bottom waters of the Bungo Channel and the Kii Channel have similar properties to those of the open ocean.
