The ^239+240Pu concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios in seawater from the eastern Indian Ocean were determined to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds (PPG)-derived Pu into the studied area. This is the first study by anyone on these Pu atom ratios in the Indian Ocean. In the West Australia Basin, the ^239+240Pu concentration was 2.89 mBq m^–3 in the surface water and increased with depth; a subsurface maximum was identified at 200 m depth and then decreased gradually with depth; its water column inventory was 32.8 Bq m^–2. The inventory-weighted mean ²⁴⁰Pu/²³⁹Pu atom ratios were 0.208 in the South Australia Basin, 0.226 in the Perth Basin, 0.242 in the West Australia Basin, 0.232 in the Bay of Bengal, and 0.225 in the Andaman Sea. The obtained ²⁴⁰Pu/²³⁹Pu ratios were clearly greater than the mean global fallout ratio of 0.18. These high atom ratios proved the presence of close-in fallout Pu from PPG nuclear tests. The relative contribution of global and PPG fallouts was evaluated using the two-end-member mixing model. The ^239+240Pu inventories originating from the PPG fallout were calculated as 2.9–14.9 Bq m^–2, which corresponded to 20–46% of the total ^239+240Pu inventory. A significant amount of the PPG-derived Pu has been transported to the eastern Indian Ocean. The proposed transport pathway accounting for the high ²⁴⁰Pu/²³⁹Pu ratio is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Mindanao Current, Indonesian Throughflow, and then spreading over the Indian Ocean by its surface circulation system.

中文翻译：

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东印度洋水体中 239Pu 和 240Pu 浓度和 240Pu/239Pu 原子比和 239+240Pu 存量的分布：太平洋试验场衍生的 Pu 通过印度尼西亚通流的传输

确定了东印度洋海水中的^239+240 Pu 浓度和²⁴⁰ Pu/ ²³⁹ Pu 原子比，以确定其 Pu 来源并提出太平洋试验场 (PPG) 衍生的 Pu 进入研究区域的传输途径。这是任何人对印度洋中这些 Pu 原子比率的首次研究。在西澳大利亚盆地，地表水中的^239+240 Pu 浓度为 2.89 mBq m ^–3并随深度增加；在 200 m 深度处发现了一个地下最大值，然后随着深度逐渐减小；其水柱库存为 32.8 Bq m ^–2。库存加权平均值²⁴⁰ Pu/ ²³⁹Pu 原子比在南澳大利亚盆地为 0.208，在珀斯盆地为 0.226，在西澳大利亚盆地为 0.242，在孟加拉湾为 0.232，在安达曼海为 0.225。获得的²⁴⁰ Pu/ ²³⁹ Pu 比率明显大于 0.18 的平均全球沉降比率。这些高原子比证明了 PPG 核试验中存在接近的沉降物 Pu。使用两端成员混合模型评估全局和 PPG 沉降的相对贡献。源自 PPG 沉降物的^239+240 Pu 库存计算为 2.9–14.9 Bq m ^–2，相当于^239+240总量的 20–46%普库存。大量 PPG 衍生的 Pu 已被运输到东印度洋。考虑到高²⁴⁰ Pu/ ²³⁹ Pu 比率的拟议运输途径是由北赤道洋流运输 PPG 衍生的 Pu，然后是棉兰老洋流，印度尼西亚通流，然后通过其表面环流系统扩散到印度洋。