摘要
采用同位素稀释ICP-MS测定法,对中国东海陆架及日本冲绳海槽的6个沉积物芯中U和Th的同位素地球化学行为进行了研究,以了解氧化还原敏感元素U在近海次氧化性沉积物中的蓄积行为,并评价其在全球海洋铀平衡中的意义。东海沉积物芯中,238U浓度及238U/232Th比值随深度变化不明显。但是在冲绳海槽沉积物芯中,238U浓度及238U/232Th比值在沉积芯表层氧化带显示较低值,然后在次氧化层随深度增加而增加。230Th和232Th浓度在所有沉积物芯中基本不随深度变化。这些结果说明,冲绳沉积物中有“自生铀”的蓄积过程发生,蓄积速率约为(47±5)～(90±8)ng/(cm2·a),与文献报道的世界其他海域次氧化性沉积区大致相当。进一步证明了U在近海次氧化性沉积区的蓄积对于全球海洋铀平衡有重要意义。“自生铀”的主要蓄积机制是海水U(Ⅵ)向沉积物迁移,在还原条件下被还原为惰性的U(Ⅳ)并被吸附在沉积物固体相上。
Concentrations of U and Th isotopes in the East China Sea and Okinawa Trough sediment cores were determined by isotope dilution inductively coupled plasma mass spectrometry （ICP-MS） to investigate the behavior of redox sensitive uranium in suboxie hemipelagie sediments and its significance in oceanic uranium balance. 238U concentrations and ^238U/^232Th activity ratios in the East China Sea sediments showed no remarkable variation with depth. However, ^238U and ^238U/^232Th ratios in the Okinawa Trough sediments were low in the surface oxidizing layer but increased where the post-oxie condition was encountered. The distribution profiles of ^230Th and ^232Th concentrations were relatively constant with depth in both the Okinawa Trough and East China Sea sediment cores. These results suggested that there has been postdepositional precipitation of authigenic uranium within the suboxic Okinawa Trough sediment column. The postdepositional precipitation rates of authigenie uranium were estimated to be （47 ±5）- （90±8） ng/（cm^2·y）. These rates were comparable to those previously reported for several anoxie sediments and this removal of uranium in the oceanic budget increases the importance of the suboxie sediment sink. A mechanism controlling precipitation of uranium may be the downward diffusion of uranium U （ Ⅵ）, reduction to U （Ⅳ） and finally precipitation to the solid phase.
出处
《地球化学》
CAS
CSCD
北大核心
2006年第3期240-248,共9页
Geochimica
基金
日本文部省科技振兴特别协助基金(MASFLEX
GCMAPS)
关键词
自生铀
氧化还原
沉积物
蓄积速率
东海
冲绳海槽
authigenic uranium
redox
sediment
accumulation rate
East China Sea
Okinawa Trough
