Temporal and spatial variations of hydrogen peroxide, organic peroxide, carbon monoxide, Fe(III) and Fe(II), which are crucial species to control the photochemical processes in coastal seawater, are investigated in the western part of the Seto Inland Sea on May 15-19, 1995. Concentrations of hydrogen peroxide and carbon monoxide wee higher at the surface and decreased with depth, while the vertical distributions of organic peroxide and soluble Fe(II) were found to be almost uniform or a little higher at the bottom layer. Soluble Fe(III) increased with depth and the concentrations at the sampling point near the mouse of the river were higher than those far from river and land, suggesting that suspended matter supplied from river and bottom of the sea was the source of soluble Fe(III). Concentrations of hydrogen peroxide, carbon monoxide and soluble Fe(II) in surface water tended to increase with solar radiation. Especially, diurnal variation of carbon monoxide was clearly in accordance with solar radiation. These results strongly suggest the photochemical formation of hydrogen peroxide, carbon monoxide an soluble Fe(II) in the surface and near-surface waters. Diurnal change of organic peroxide was the reverse of that, the concentrations of organic peroxide in the daytime were lower than those during the nighttime.
