International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco; Sorbonne Universités, Université Pierre et Marie curie, UMR 7093, Observatoire Océanologique de Villefranche, Laboratoire d'Océanographie de Villefranche-sur-Mer, France.
International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco.
Sci Total Environ. 2017 Oct 1;595:178-190. doi: 10.1016/j.scitotenv.2017.03.137. Epub 2017 Apr 4.
The evolution of Cs, Np and Pu at the DYFAMED station (NW Mediterranean) is discussed in relation to physical processes, downward fluxes of particles, and changes in the main input sources. The data set presented in this study represents the first complete Np vertical profiles (0.12-0.27μBqL), and constitutes a baseline measurement to assess future changes. A similar behavior of Cs and Np has been evidenced, confirming that Np behaves conservatively. While the Cs decrease has been driven by its radioactive decay, the vertical distribution of Np has not substantially changed over the last decade. In the absence of recent major inputs, a homogenization of their vertical distribution occurred, partly due to deep convection events that became more intense during the last decade. In contrast, Pu surface levels in the NW Mediterranean waters have fallen in the past four decades by a factor of 5. This decrease in surface has been balanced by higher concentrations in the deep-water layers. A first estimate of the downward Pu fluxes in the NW Mediterranean Sea is proposed over more than two decades. This estimation, based on the DYFAMED sediment trap time-series data and published Pu flux measurements, suggests that sinking particles have accounted for 60-90% of the upper layer (0-200m) Pu inventory loss over the period 1989-2013. The upper layer residence time of Pu is estimated to be 28years, twice as long as the residence time estimated for the whole western Mediterranean (15years). This difference highlights the slow removal of Pu in the open waters of the NW Mediterranean and confirms that most of the Pu removal occurs along the coastal margin where sedimentation rates are high.
本文讨论了西北地中海 DYFAMED 站（NW 地中海）中 Cs、Np 和 Pu 的演化，涉及物理过程、颗粒向下通量以及主要输入源的变化。本研究中提出的数据集代表了第一个完整的 Np 垂直剖面（0.12-0.27μBqL），构成了评估未来变化的基线测量。Cs 和 Np 的相似行为已经得到证实，这表明 Np 表现出保守性。虽然 Cs 的减少是由于其放射性衰变所致，但 Np 的垂直分布在过去十年中并没有实质性变化。在没有最近主要输入的情况下，它们的垂直分布发生了均匀化，部分原因是过去十年中深层对流事件变得更加剧烈。相比之下，过去四十年中，西北地中海水域中 Pu 的表层水平下降了 5 倍。这种表层的减少被深水区浓度更高所平衡。提出了过去二十多年来西北地中海海 Pu 向下通量的首次估计。该估计值基于 DYFAMED 沉积物捕集器时间序列数据和已发表的 Pu 通量测量值，表明下沉颗粒在 1989-2013 年期间占上层（0-200m）Pu 库存损失的 60-90%。Pu 的上层停留时间估计为28 年，是整个西地中海估计停留时间（15 年）的两倍。这种差异突出了 Pu 在西北地中海开阔水域中的缓慢去除，并证实了大部分 Pu 的去除发生在沉积物速率较高的沿海水域。
