230Th232Th systematics in the central Pacific Ocean: The sources and the fates of thorium
230Th232Th systematics in the central Pacific Ocean: The sources and the fates of thorium
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DOI：
10.1016/0012-821x(96)00017-9
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发表时间：
1996-04
影响因子：
5.3
通讯作者：
M. Roy‐Barman;J. Chen;G. Wasserburg
中科院分区：
文献类型：
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作者：
M. Roy‐Barman;J. Chen;G. Wasserburg
使用同位素稀释和热电离质谱法沿太平洋中部的深度剖面测量了未过滤和过滤海水样品的 232Th 和 230Th。 232Th浓度从25 m以下到2000 m以上（45–60 × 106atom cm−3）相当恒定，然后向底部快速增加（4000 m处为119–360 × 106atom cm−3）。 230Th浓度随着深度从25 m处的3×103atom cm−3到4000m处的110×103atom cm−3线性增加。重复分析的再现性和曲线的规律性证明了该程序的可靠性。然而，同一深度的不同样品之间缺乏可重复性必须用自然变异或样品采集过程中的污染来解释。由于非常低的 232Th 浓度和相对较高的 230Th 浓度，230Th/232Th 比率可高达 1.6 × 10−3。 232Th 颗粒 (> 0.2 μm) 上的 Th 量与溶液中 Th 量的比率 (≈ 0.37) 显着高于 230Th (≈ 0.18)。这些数据根据专门处理颗粒传输的模型进行解释，假设颗粒和海水之间存在局部平衡。在 25 m 处测得的相对较高的 230Th 浓度和 230Th/232Th 比值与约 100 m 的混合层一致。 230Th 随深度的线性增加意味着在 Th 去除时间尺度上，涡流扩散的影响对于大部分水柱来说可以忽略不计。该分布与通过对以恒定速度沉降的颗粒的可逆吸收而进行的 230Th 的传输一致。 232Th 数据与该模型不一致，它们表明携带 232Th 的粒子在地表和 4000 米之间经历了 70% 的质量损失，并且必须遵循不同的传输规则。 230 钍和 232 钍传输的这种差异证明了这些同位素在颗粒形成以及随后在水柱中的再矿化和重新包装过程中的独特行为。 230Th 和 232Th 的不同形态可能是由于它们在海洋中的独特来源（因为 230Th 在溶液中产生，232Th 由碎屑物质携带）以及它们各自的包装机制（目前尚不清楚）来解释。
232Th and230Th of unfiltered and filtered sea water samples were measured along a depth profile of the central Pacific Ocean using isotopic dilution and thermal ionization mass spectrometry. The232Th concentration is rather constant from below 25 m down to over 2000 m (45–60 × 106atom cm−3) and it then increases rapidly towards the bottom (119–360 × 106atom cm−3at 4000 m). The230Th concentration increases linearly with depth from 3 × 103atom cm−3at 25 m to 110 × 103atom cm−3at 4000 m. The reproducibility of replicate analyses and the regularity of the profiles demonstrate the reliability of the procedure. However, some lack of reproducibility among different samples from the same depth has to be explained by natural variability or by contamination during sample collection. Due to the very low232Th concentrations and relatively high230Th concentrations, the230Th/232Th ratios can be as high as 1.6 × 10−3. The ratio of the amount of Th on particles (> 0.2 μm) to the amount of Th in solution is significantly higher for232Th (≈ 0.37) than for230Th (≈ 0.18). These data are interpreted in terms of a model that specifically treats particle transport assuming local equilibrium between particles and sea water. The relatively high230Th concentrations and230Th/232Th ratios measured at 25 m are consistent with a mixed layer of about 100 m. The linear increase in230Th with depth implies that the effect of eddy diffusion is negligible for most of the water column over the Th removal time scale. This profile is consistent with transport of230Th by reversible uptake on particles settling with a constant velocity. The232Th data are inconsistent with this model and they suggest that particles carrying232Th experience 70% of mass loss between the surface and 4000 m and must follow different transport rules. This difference in the transport of230Th and232Th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent remineralization and repackaging in the water column. Different speciation of230Th and232Th may be explained by their distinctive sources in the ocean (as230Th is produced in solution and232Th is carried by detrital material) and by their respective packaging mechanisms, which are not yet known.