PB-210 FLUXES AND SEDIMENTATION-RATES AN THE LOWER CONTINENTAL-SLOPE BETWEEN TAIWAN AND THE SOUTH OKINAWA TROUGH

Pb-210 and Ra-226 have been measured on II cores taken from the continental slope between northern Taiwan and the western South Okinawa Trough, Ra-226 activities generally fall between 0.5 and 2 dpm g(-1). Pb-210 activities are widely variable in these cores: negligible excess Pb-210 (or no Pb-210 flux) is observed on the upper and middle slope while large excess Pb-210 values (50-90 dpm g(-1)) are present on the lower slope. Sedimentation rates estimated from the excess Pb-210 profiles of the cores range from 0.09 to 0.52 cm y(-1) (0.08-0.42 g cm(-2) y(-1)) for the lower slope and decrease toward the deeper (eastern) slope. Excess Pb-210 inventories and the Pb-210 fluxes calculated from the lower slope are 320-840 dpm cm(-2) and 10-26 dpm cm(-2) y(-1), respectively, assuming a steady-state input at each site for the past 100 years. Atmospheric input of Pb-210 and local production from Ra-226 do not account for the observed fluxes. Two alternative explanations are proposed: (1) boundary scavenging coupled with the Kuroshio water flowing through the area; or (2) downslope transport of high Pb-210 activity fine-grained particles from the shelf and upper/middle slope to the lower slope where they are deposited.