title: Temporal evolution of137Cs,237Np, and239+240Pu and estimated vertical239+240Pu export in the northwestern Mediterranean Sea.
abstract: The evolution of137Cs,237Np and239+240Pu 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 complete237Np vertical profiles (0.12-0.27μBqL-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 the137Cs decrease has been driven by its radioactive decay, the vertical distribution of237Np 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,239+240Pu 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 downward239+240Pu 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 published239+240Pu 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.
authors.affiliation: 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. Electronic address: bressac@obs-vlfr.fr.
authors.forename: M
authors.initials: M
authors.lastname: Bressac
authors.affiliation: International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco. Electronic address: I.N.Levy@iaea.org.
authors.forename: I
authors.initials: I
authors.lastname: Levy
authors.affiliation: Centro Nacional de Aceleradores (Universidad de Sevilla, Consejo Superior de Investigaciones Científicas, Junta de Andalucía), Thomas Alva Edison 7, 41092 Seville, Spain. Electronic address: echamizo@us.es.
authors.forename: E
authors.initials: E
authors.lastname: Chamizo
authors.affiliation: International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco; National Institute of Standards and Technology, Gaithersburg, MD 20899-8462, USA. Electronic address: jerome.larosa@nist.gov.
authors.forename: J J
authors.initials: JJ
authors.lastname: La Rosa
authors.affiliation: International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco; Comenius University, Faculty of Mathematics, Physics and Informatics, 84248 Bratislava, Slovakia. Electronic address: povinec@fmph.uniba.sk.
authors.forename: P P
authors.initials: PP
authors.lastname: Povinec
authors.affiliation: International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco.
authors.forename: J
authors.initials: J
authors.lastname: Gastaud
authors.affiliation: International Atomic Energy Agency, Environment Laboratories, MC 98012, Monaco.
authors.forename: B
authors.initials: B
authors.lastname: Oregioni
keywords: DYFAMED; Marine tracer; Neptunium-237; Northwestern Mediterranean; Plutonium isotopes; Vertical export