Abstract This study elucidates the processes that may determine the distributions of Mn and other trace metals on the slope of the southern Okinawa Trough. In addition to salinity and temperature, large-volume seawater samples were collected for analyzing dissolved manganese (DMn), particulate manganese (PMn), suspended, particulate organic carbon (POC), pH and dissolved CO2 (TCO2 ) during June-July of 1998, 1999 and 2000. Concentrations of DMn and PMn in a transect decrease generally seaward from the shelf break. However, anomalous distributions of DMn and PMn occur usually between 600 m and 900 m in many deep profiles. Such distribution patterns are probably influenced by the lateral transport of metals released from slope sediments or from the plumes of submarine venting systems. For example, dissolved manganese generally decreases with depth in the oxygenated condition, but in the study area unusual high DMn concentrations were observed commonly at depth 400 m, 600 m, 800 m and 1200 m. The unusual Mn signals become weak, in general, from the South Mien-Hua Canyon to the North Mien-Hua Canyon. The higher concentration of PMn sometimes was observed in deep stations than in shallow stations at the same depth implying that processes other than lateral transport may account for the distributions. Images obtained from EK-500 showed that submarine venting systems exist in anomalous Mn distribution areas. Anomalous distributions of PMn and Kd match DMn unusual distributions very well. Besides, the distribution of TSM is closely related to PMn distributions (R=0.433, p=0.01). Although the distribution of pH data appears to be normal, total alkalinity and total CO2 display anomalous distributions coincidently with those Mn unusual distributions. Meanwhile, the ratio (PMn/PAl) is higher for those unusual Mn distributions, and this is likely the effect of submarine venting.