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Le néodyme (Nd)

Le néodyme (Nd). Le Nd est une terre rare (REE) 14 éléments, remplissage couche 4f Fractionnement entre les REE (anomalie cerium). REE: their oceanic pattern. German et al,1995. Nd : Masse atomique A = 144,24 Numéro atomique Z = 60 7 isotopes : - 142 : 27,13 % 143 : 12,18 %

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Le néodyme (Nd)

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  1. Le néodyme (Nd) Le Nd est une terre rare (REE) 14 éléments, remplissage couche 4f Fractionnement entre les REE (anomalie cerium)

  2. REE: their oceanic pattern German et al,1995

  3. Nd : Masse atomique A = 144,24 Numéro atomique Z = 60 7 isotopes : - 142 : 27,13 % • 143 : 12,18 % • 144 : 23,8 % - 145 : 8,3 % • 146 : 17,19 % • 148 : 5,76 % • 150 : 5,64 % Les 7 isotopes sont stables Le 143Nd provient de la désintégration du 147Sm : Composition isotopique du Nd : 147Sm 143Nd + a T1/2=1011 yr

  4. Concentration et composition isotopique : des partenaires complémentaires Ieau>Ipart Dissolution Re-precipitation Concentrations reflètent une BALANCE Composition isotopique un ECHANGE C C I I

  5. Modèle CHUR : « Chondritic Uniform Reservoir » valeur initiale 143Nd/144Nd CHUR = 0.50684 valeur actuelle 143Nd/144Nd CHUR = 0.512638 Fractionnement Nd / Sm lors de la différentiation manteau/ croûte continentale LREE préfèrent le liquide résiduel = Nd ira plus dans la croûte que Sm Sm/ Nd appauvri dans le magma crustal et enrichi dans les basaltes La croûte continentale est peu radiogénique : 143Nd/144Nd < 0.512638 MORB, volcans récents très radiogéniques : 143Nd/144Nd > 0.512638

  6. Earth Old continent Volcanic material eNd distribution on the earth surface:heterogeneity Jeandel et al, 2007

  7. Thermohaline Circulation -15 -5 eNd oceanic distribution follows the general circulation (in the modern ocean and in the sediment)

  8. eNd: Present day oceanic distribution When reaching the oceans, Nd is redistributed by the circulation Its residence time is of the order of 500-1000 y (Tachikawa et al., 2003) Number of data The Atlantic-Pacific eNd variation follows the thermohaline circulation -4 -13 Lacan et al, 2012

  9. Conservativity ofeNd: NADW: eNd = -13.5 Far from any lithogenic input: eNd behaves conservatively South North . (von Blanckenburg 1999)

  10. Goldstein and Hemming,2003

  11. eNdas paleo-tracer High resolution Nd record Nd: Piotrowski et al. , EPSL 2004; Science 2005 d13C: Charles et al. 1996, Ninnemann et al. 2000

  12. The Nd paradox: when concentration budget is balanced, eNd budget is not A negative term is missing A positive term is missing - 1 1 . 3 - 6 . 7 - 1 1 . 2 ± 1 . 1 -4 3 ± 2 . 0 . - 8 . 3 - 6 . 3 - 8 6 . - . 6 8 - 1 1 . 2 - 9 . 1 ± 0 . 1 - 3 ± 2 . 5 -4 6 ± 1 . 0 . - 1 0 . 1 ± 1 . 8 ( - 1 4 . 7 ± 1 . 2 ) - 8 . 3 - 1 0 . 9 - 6 . 7 - 1 1 . 1 ± 2 . 1 - 8 . 5 ± 0 . 4 - 5 . 5 ± 1 . 7 North Atl. Deep Atl. Austral Indo-Pacific (Tachikawa, Athias, Jeandel, 2003) end distribution calculated using all the dissolved riverine fluxes and 2-30% aeolian flux (Goldstein et al, 1987; Greaves, Elderfield…)  Exchange processes are required. Margins?

  13. Nd (and Fe) subsurface enrichments originate from the PNG Dissolved iron (Coale et al, 1996) eNd=-1.6 ±0.3 eNd=+7 eNd=-4.3 ±0.3 Constant Nd concentration Coale et al. 1996 Lacan et Jeandel 2001 EPSL Kilo Moana EUC Fe Cruise, 2006 • Input fromthe Papouasie-New Guinea margins

  14. Coupling Nd concentration and isotopes: Boundary Exchange "BOUNDARY EXCHANGE«  - quantifiable using Nd IC - invisible with concentrations only Lacan and Jeandel, 2005

  15. Modélisation cycle Nd et eNd (Arsouze, 2007, 2008 and Arsouze et al., 2009.) • But: résoudre «Nd paradox » afin de réconcilier concentrations Nd et distributions IC => representation explicite : - sources : source reliée BE ? - processus : échange dissous /particules ? (Bertram and Elderfield, 1993; Tachikawa et al, 1999; Nozaki and Alibo, 03 ; Oka et al, 08) • Simulation simultanée Nd concentration et εNd : Modèle couplant dynamique / biogéochimie NEMO/PISCES. • Approche plus réaliste va permettre • Modéliser le cycle océanique du Nd • Améliorer la quantification des apports CO

  16. Existing Nd IC data (stations with at least 3 data)

  17. 13 0 -10 -20 -30 -42 eNd interpolated along the oceanic margin eNddata compilation (Jeandel et al, Chem. Geol., 07)

  18. Nd cycle 1 2 2 1 1 1 3 Determine the sources Marine particle fields Poussières atmosphériques Apports fluviaux Remobilisation sédimentaire Scavenging réversible eNdonly Marge continentale Sédimentation 3000m eNd and [Nd] Explicit simulation : sources : dissolved rivers, atmospheric dusts, sediment remobilisation (BE) Sedimentary fluxes ( = Σ Sources at steady state) 3 Dissolved/particles interactions, requiring particle fields

  19. PISCES biogeochemical model Reversible scavenging model PISCES Particles Dissolved phase A D R WS 3 m/d 50-300 m/d A: Adsorption D: Desorption R: Remineralisation WS: Particle settling velocity PISCES: Two classes of particules • Small particles (POCs) settling velocity : 3m/d • Large particles (POCb, CaCO3, SIO2, litho) settling velocity: 50-300 m/d

  20. After many sensitivity tests: synthesis (Arsouze, 2008; Arsouze et al, 2009) • Sources : Dissolved rivers : FR = 2.6 108 g(Nd)/a Dusts : FA = 1.0 108 g(Nd)/a Sedimentary dissolution: FBE = 1.1 1010 g(Nd)/a [Nd] Model • Partition coefficients : POCsmall : APOCs/Ad = 1.10-3 POCb / CaCO3 / bSi / litho : Ap/Ad = 2.10-5 eNd eNd Model 800 - 5000 m Data

  21. FA FBE FR Model coupling OGCM and Nd cycle (all sources&sinks) (Arsouze, 2008; Arsouze et al, 2009) eNd 800 - 5000 m • . • BE isTHE major source term (>95% of the total : 1.1 1010 g(Nd)/an). • Dustand dissolved river inputs significant in the Atlantic surface waters. • Reversiblescavengingrequired in order to reconciliate the Nd and εNdwithdepth and along the thermohaline circulation • (in agreement withH. Elderfield and Ed Sholkovitzearlierhypothesis) • Continental inputs & margins:major role in the Nd oceanic cycle.… • And for the other chemical elements?

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