Characteristics of radionuclides in sediments collected from the Beibu Gulf and influence factors
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摘要: 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。本研究有利于掌握滨海核电发展背景下的北部湾海洋环境中放射性核素水平,揭示核素的“蝴蝶”状分布特征和控制因素,探索基于放射性核素的地球化学新指标在海洋沉积过程中的应用。Abstract: 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.
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Key words:
- radionuclide /
- nuclear power plant /
- redox-sensitive element /
- geochemical proxy /
- sedimentation
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图 3 涠洲岛(WZ)与三娘湾(SN)沉积物柱状样中放射性核素238U(a)、226Ra(b)、228Ra(c)、40K(d)比活度剖面图
图中虚线和点线分别代表涠洲岛和三娘湾的柱样中核素比活度平均值
Fig. 3 Vertical profiles of specific activities of 238U(a), 226Ra(b), 228Ra(c), and 40K(d) in sediment cores from the stations of WZ and SN
The average value was indicated by the dashed line and dotted line for WZ and SN, respectively
表 1 不同海域的表层沉积物中238U、226Ra、228Ra、40K含量(单位:Bq/kg)
Tab. 1 Activities of 238U、226Ra、228Ra、40K in surface sediments from distinct sea regions (unit: Bq/kg)
地区 238U 226Ra 228Ra 40K 参考文献 范围 平均值 范围 平均值 范围 平均值 范围 平均值 大连湾 26.4~47.0 34.9 11.2~25.3 19.3 — — 669~807 746 [24] 莱州湾 — 54.4±11.7 — 28.6±4.30 — 57.9±9.70 — 542±21.0 [25] 胶州湾 32.4~56.2 39.2±8.80 20.6~44.1 26.5±3.30 35.7~53.3 40.3±4.80 607~732 688±58.0 [26] 长江口 14.1~62.3 32.8±10.6 13.7~52.3 24.3±7.4 26.1~71.9 40.9±9.4 392~898 628±135 [27] 厦门海域 11.5~65.1 40.2 27.5~40 32.4 49.9~94.3 69.3 510~1096 692 [28] 大亚湾 36.6~64.1 49.2±3.9 15.6~29.7 20.9±0.7 40.3~52.7 47.2±1.9 360~482 432±19 [29] 黄茅海—广海湾 66.5~98.8 77.4 32.0~48.7 36.6 49.7~64.8 58.1 505~644 571 [30] 阳江海域 75.2~102.0 82.4±5.2 32.6~38.6 35.5±2.0 40.9~70.6 57.1±3.1 580~660 621±29 [31] 白龙半岛 12.0~87.0 48.3±20.2 10.3~51.8 32.4±9.40 13.2~72.9 46.1±13.4 69.6~514 355±125 [32] 南海东北部 21.2~59.0 35.4±3.0 25.9~32.4 27.7±1.3 22.6~65.2 44.9±5.9 273~686 538±52 [34] 海南岛东部 6.0~33.2 21.7±6.4 12.6~25.5 19.0±1.0 — — — — [33] 南沙海域 19.9~70.2 — 14.1~147 — 11.0~80.0 — 155~868 — [35] 中国土壤 7.30~449 38.5±21.1 2.80~533 37.6±23.4 10.3~1844 54.6±51.3 ND~1548 584±183 [36] 南海珊瑚礁 22.1~38.2 29.0±5.09 1.47~9.39 3.34±2.51 0.51~14.4 5.08±4.91 2.15~154 24.4±49.1 [20] 北部湾 5.07~43.2 24.7±11.6 4.33~42.2 22.2±10.7 7.76~88.8 34.4±18.7 0.16~588 253±192 本文 注:"—"代表没有数据。 表 2 不同海域表层沉积物的辐射环境质量评价
Tab. 2 Assessment of environmental radiation quality for sediments from other sea regions
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