Scavenging phenomenon elucidated by 234Th/238U disequilibrium in the surface water of the Taiwan Strait

Abstract

Concentrations of dissolved (234Thd) and particulate (234Thp) 234Th in surface water at 38 stations in the Taiwan Strait were determined for samples collected in May 2006. The spatial distribution of 234Th in the Taiwan Strait is controlled by advective input of Kuroshio Branch Water via the Peng-Hu Channel and fast removal due to the high input of riverine particulates from the Cho-Sui River. A scavenging model involving physical transport was applied to the 234Thd and 234Thp data to estimate scavenging and removal rates of 234Th. Estimated scavenging rate ranges from 32 to 703 dpm m-3 d-1 and the removal rate ranges from 24 to 560 dpm m-3 d-1. Using 234Th as a proxy of particulate organic carbon, we estimate that the removal rate of POC from surface water of the Taiwan Strait ranges from 0.3 ± 1.5 mmol-C m-3 d-1 off southwestern Taiwan to 10.2 ± 3.5 mmol-C m-3 d-1 in the central Taiwan Strait.