Temporal evolution of Cs-137, Np-237, and Pu239+240 and estimated vertical Pu239+240 export in the northwestern Mediterranean Sea - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Science of the Total Environment Année : 2017

Temporal evolution of Cs-137, Np-237, and Pu239+240 and estimated vertical Pu239+240 export in the northwestern Mediterranean Sea

Résumé

The evolution of Cs-137, Np-237 and Pu239+240 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-237 vertical profiles (0.12-0.27 mu Bq L-1), 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-137 decrease has been driven by its radioactive decay, the vertical distribution of Np-237 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, Pu239+240 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 Pu239+240 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 Pu239+240 flux measurements, suggests that sinking particles have accounted for 60-90% of the upper layer (0-200 m) Pu inventory loss over the period 1989-2013. The upper layer residence time of Pu is estimated to be similar to 28 years, twice as long as the residence time estimated for the whole western Mediterranean (similar to 15 years). 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. (C) 2017 Elsevier B.V. All rights reserved.

Domaines

Océanographie
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Dates et versions

hal-03502949 , version 1 (26-12-2021)

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M. Bressac, I. Levy, E. Chamizo, J. J. La Rosa, P. P. Povinec, et al.. Temporal evolution of Cs-137, Np-237, and Pu239+240 and estimated vertical Pu239+240 export in the northwestern Mediterranean Sea. Science of the Total Environment, 2017, 595, pp.178-190. ⟨10.1016/j.scitotenv.2017.03.137⟩. ⟨hal-03502949⟩
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