THE EFFECT OF A CYCLONIC EDDY ON THE DISTRIBUTION OF LITHOGENIC PARTICLES IN THE SOUTHERN EAST CHINA SEA

Off northeastern Taiwan, the collision between the Kuroshio Current (K C) and the East China Sea (ECS) shelf forms a branch current (Kuroshio Branch Current) on the shelf, and the counterclockwise deflection of the subsurface Kuroshio water annually generates a cyclonic eddy, abou t 70 km in diameter, over the shelf-slope in summer. In this study, th e total suspended matter collected from varying water depths over the eddy during August 1994 has been analyzed for Al, which is used as an indicator element to trace lithogenic particle transport. Simultaneous ly, the measurements of current field, using the Shipboard Acoustic Do ppler Current Profiler, and hydrography have also been conducted on th e same cruise during the seawater sampling. These offer an opportunity for direct examination of the relationships between circulation patte rns and distributions of Lithogenic particles to further establish a t ransport model for lithogenic particles. However, we must emphasize th at this is a representative case for the export of terrigenous suspens ions delivered from rivers, although the observation was made only in summer. The spatial distribution of particulate Al (PAI) in the upper water displays an ''Omega'' shape with high concentrations of PAl clos e to the Taiwan coast and around the eddy center. II suggests that Tai wan-derived riverborne particulates are the main source for the lithog enic particles in the upper water of the study area. Moreover, the PAl in the upper water is essentially constrained by the cyclonic eddy, a nd the entrainment and subsequent accumulation of lithogenic particles occur at the eddy center. The 6 mu g/l contour of PAl in the upper wa ter almost matches the western boundary of the main stream and branch of the KC across the ECS shelf-slope, and two concentration provinces of PAl can be identified from this contour: one to the west is larger and variable and the other to the east is smaller and uniform. This in dicates that the main stream and branch of the KC may confine terrigen ous particles to the inshore area where mixing of the lithogenic parti cle-rich coastal water and the clearer Kuroshio water occurs and may a ct as a barrier to the offshore transport of terrigenous particles to regions farther away from the coast, toward the north and east. In thi s study, a conceptual model for the transport of lithogenic particles in the water of the southern ECS is proposed according to the spatial distributions of PAI. This model suggests that the cyclonic eddy at th e turning site of the KC may be the important conduit for the indirect transport of terrigenous particles from the ECS shelf and slope to th e southern Okinawa Trough or the Pacific Ocean. This is also a valuabl e example of the role of the eddy system in regulating the distributio n and transport of terrigenous particulates.