Particulate fluxes, 210Pb and 210Po measured from sediment trap samples in a canyon off northeastern Taiwan

Three time-series sediment-trap moorings were deployed and recovered within a canyon of the continental slope off northeastern Taiwan at different time periods during 1992 and 1993. The trapped particulate samples were determined for apparent mass flux, size distribution and activities of Pb-210 and Po-210. The apparent mass fluxes determined from each trap deployed at about 300-600 m depth varied periodically with the mean flux from each trap ranging between 5 and 72 g m(-2) d(-1). These values were at least an order of magnitude greater than those observed else where. The mass flux increased with the depth deployed, and the synchronized periodic variation was related to the amplitude of the tidal velocity oscillation, i.e. high mass flux occurred when the amplitude was large. The trapped particulates were mainly silt and sand while the sediments in the canyon were mainly silt and clay. High mass flux was usually due to high sand and/or silt content in the trapped particulates which were most likely transported laterally from the shelf and upper slope areas. Except for a few samples, Po-210 was lower than Pb-210 with a mean Po-210/Pb-210 activity ratio of about 0.6. The low and variable activity ratio might suggest that Pb-210 was preferentially scavenged by advecting and settling particulates of terrigenous origin. Po-210, known to be biophilic, might remain associated with the suspended organic particulates which could be dissolved or not collected by the traps. High mass flux was generally associated with high sand fraction and low concentrations of the two nuclides, and vice versa, indicating a dilution effect of the sand particles which contained little nuclides. (C) 1998 Elsevier Science Ltd. All rights reserved.