Particle Scavenging in the Nearshore Waters of Western Taiwan: 234 Th / 238 U Disequilibrium Elucidation
Date Issued
2006
Date
2006
Author(s)
Tsai, Jing-Ru
DOI
zh-TW
Abstract
During November 19-23, an intensive sampling expedition in the coastal region off western Taiwan (Cruise #: ORII-1248) was carried out. A total of 27 stations were occupied to collect large-volume seawater for dissolved and particulate 234Th measurements. In addition to the basic hygrographic parameters (T, S, fluorescence and light transmission), separate samples for the measurements of nutrients, particulate organic carbon, primary productivity and bacteria production were also collected. The investigation is aimed to provide information of particle dynamics in the nearshore waters of highly populated west coast of Taiwan.
Latitudinal distributions of fluorescence and light transmission evidently indicate that particle compositions in the northern and southern regimes are very different. Divided by Cho-Shuei River system at about 23°40’N, particles in the northern regime are characterized by terrigeneous characteristics whereas those in the southern regime are dominated by biological origin. Resulted from high turbidity, the dissolved 234Th activities are extremely low, ranging between <0.1 dpm/L and 0.75 dpm/L, and show drastic latitudinal variability. Low dissolved 234Th activities are usually associated with the five river systems reported with high particulate loads. Particulate 234Th activities showed less drastic change than dissolved 234Th in the southern regime (average value of ~0.3 dpm/L), whereas those in the northern regime are mirror-imaged with dissolved 234Th activities. Large deficiency of 234Th relative to 238U indicates an active scavenging-removal phenomena prevailing in the nearshore waters. An advection-scavenging-removal model was be adopted to derive scavenging and removal rates of 234Th. Dissolved 234Th residence time and particulate 234Th residence time are <0-16 days and <0-10 days, respectively.
Subjects
清除現象
分布係數
水平傳送清除模式
scavenging elucidation
Kd
advection-scavenging-removal model
Type
thesis
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