Abstract:The vertical distributions of managanese at a station in the southern Okinawa Trough were investigated bi-monthly by analyzing the dissolved manganese in filtered seawaters. The analysis of every survey showed the elevated concentrations of dissolved manganese between depths of 600 and 900 m, with the peak at about 800 m and a maximum concentration of 5-8 nM. Repeated observations showed that the dissolved manganese maximum always appeared within a narrow range of £m£cbetween 27.1 and 27.2. The results not only confirmed the previous report of a mid-depth Mn maximum, but also revealed that the dissolved manganese is one of the major forms in the mid-depth manganese maximum. In this study, we conclude that a persistent mid-depth maximum of dissolved manganese exits in the southern Okinawa Trough off northeastern Taiwan.