北部湾沉积物中放射性核素的分布特征与控制因素

北部湾是我国大西南地区重要的海上通道,也是我国重要的渔场之一。本研究利用高纯锗γ谱仪系统分析北部湾表层和柱状沉积物中4种最主要的天然放射性核素(²³⁸U、²²⁶Ra、²²⁸Ra、⁴⁰K)含量和分布特征。结果显示,北部湾沉积物中放射性核素含量低于我国大部分海域的结果,高于珊瑚礁区的极低放射性水平的结果。北部湾沉积物中4种核素都存在"蝴蝶"状空间分布特征,该特征主要源于沉积物粒径的非线性调控,且与沉积物总有机碳浓度存在正相关。此外,利用Mn和²¹⁰Pb所指示的氧化还原状态和物理/生物扰动过程也可以对柱状沉积物中氧化还原敏感型核素(比如,²³⁸U)分布产生一定的影响。本文从²³²Th/²³⁸U、⁴⁰K/²³⁸U、²²⁶Ra/²³⁸U活度比值角度,发现北部湾沉积物具有典型的陆源沉积物特征,且显著不同于南海珊瑚礁区中生源沉积物特征。本研...

Characteristics of radionuclides in sediments collected from the Beibu Gulf and influence factors

The Beibu Gulf is not only a key sea passage in the southwestern China but also one of important fishing grounds in the South China Sea (SCS). In this study, naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in surface sediments and sediment cores of the Beibu Gulf were comprehensively analyzed using high purity germanium (HPGe) γ spectrometry. Our results indicated that radioactivity level of sediments in the Beibu Gulf was lower than that in most of China's seas and was higher than the extremely low radioactivity level of sediments in coral reefs. All nuclides in surface sediments of the Beibu Gulf had a spatial distribution of “butterfly pattern”, attributing to the non-linear regulation of sediment grain size and positive role of total organic carbon in sediment. Additionally, redox state and physical/biological disturbance derived from the proxies of Mn and 210Pb could also affect vertical distribution of redox-sensitive nuclide (eg, 238U) in sediment cores. On the basis of the 232Th/238U, 40K/238U, and 226Ra/238U activity ratio, we found that sediments of the Beibu Gulf had terrigenous characteristics, which were significantly different from biogenic sediments in coral reefs. Our study provided radioactivity level in the Beibu Gulf under the background of the rapid development of nuclear power plant, revealed the "butterfly pattern" of radionuclides and their influence factors, and explored the feasibility of novel geochemical proxies based on radionuclides in marine sedimentation.