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 = 144,24Numéro 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 + T1/2=1011 yr

4

CHUR144

143SAMPLE

144

143

Nd 101

Nd

Nd

Nd

Nd

C I

C

I

Concentration et composition isotopique : des partenaires complémentaires

Concentrations reflètent une BALANCE

Composition isotopiqueun ECHANGE

Ieau>Ipart

Dissolution

Re-precipitation

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

Modèle CHUR : « Chondritic Uniform Reservoir »

La croûte continentale est peu radiogénique :

143Nd/144Nd < 0.512638

MORB, volcans récents très radiogéniques :

143Nd/144Nd > 0.512638

Jeandel et al, 2007

1050 Nd

Oldcontinent

Volcanicmaterial

Earth

Nd distribution on the earth surface:heterogeneity

Thermohaline Circulation

Nd oceanic distribution follows the general circulation(in the modern ocean and in the sediment)

-15 -5

The Atlantic-Pacific Nd variation follows the thermohaline circulation

Its residence time is of the order of 500-1000 y(Tachikawa et al., 2003)

When reaching the oceans, Nd is redistributed by the circulation

Num

ber

of d

ata

Nd: Present day oceanic distribution

-13 -4Lacan et al, 2012

Conservativity of Nd:

(von Blanckenburg 1999)

NorthSouth

.

NADWNd = -13.5Far from any lithogenic input: Nd behaves conservatively

Goldstein and Hemming,2003

High resolution Nd High resolution Nd recordrecord

Nd: Piotrowski et al. , EPSL 2004; Science 2005 13C: Charles et al. 1996, Ninnemann et al. 2000

Nd as paleo-tracer

-3 ± 2.5

-4 .3±2.0

-4 .6±1.0

-5.5±1.7

-9.1±0.1

-8.5±0.4

-11.2±1.1

-10.1±1.8

-11.1±2.1

(-14.7±1.2)

- 1 1 .2- 8 .6

- 1 1 .3

- 1 0 .9 - 8 .3

- 8 .3

- 6 .7

- 6 .3- 6.8

- 6 .7

North Atl. Deep Atl.

(Tachikawa, Athias, Jeandel, 2003)

Indo-PacificAustral

The Nd paradox: when concentration budget is balanced, Nd budget is not

nd distribution calculated using all the dissolved riverine fluxes and 2-30% aeolian flux (Goldstein et al, 1987; Greaves, Elderfield…)

Exchange processes are required. Margins?

A negative term is missing

A positive term is

missing

Nd=-4.3 ±0.3

Nd=-1.6 ±0.3

Nd=+7

Lacan et Jeandel 2001 EPSL

Coale et al. 1996

Dissolved iron (Coale et al, 1996)

Input from the Papouasie-New Guinea margins

Nd (and Fe) subsurface enrichments originate from the PNG

Constant Nd concentration

Kilo Moana EUC Fe Cruise, 2006

Coupling Nd concentration and isotopes:Boundary Exchange

"BOUNDARY EXCHANGE« - quantifiable using Nd IC- invisible with concentrations only

Lacan and Jeandel, 2005

(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 CO

Modélisation cycle Nd etNd

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

13

0

-10

-20

-30

-42

Nd interpolated along the oceanic margin

Nd data compilation

(Jeandel et al, Chem. Geol., 07)

Nd cycle

3 Dissolved/particles interactions, requiring particle fields

Marine particle fieldsDetermine the sources

sources : dissolved rivers, atmospheric dusts, sediment remobilisation (BE)1

Sedimentary fluxes ( = Σ Sources at steady state) 2

Nd only3000m

Marge continentale

3Scavenging réversible

Poussières atmosphériquesApports fluviaux

Remobilisation sédimentaire

1

11

Sédimentation

2

Nd and [Nd]

Explicit simulation :

PISCES

3 m/d 50-300 m/d

PISCES: Two classes of particules • Small particles (POCs) settling velocity : 3m/d• Large particles (POCb, CaCO3, SIO2, litho)

settling velocity: 50-300 m/d

PISCES biogeochemical model

WS

Dissolved phase Particles

A

D

R

Reversible scavenging model

A: AdsorptionD: DesorptionR: RemineralisationWS: Particle settling velocity

• Partition coefficients : POCsmall : APOCs/Ad = 1.10-3

POCb / CaCO3 / bSi / litho : Ap/Ad = 2.10-5

• Sources :Dissolved rivers : FR = 2.6 108 g(Nd)/aDusts : FA = 1.0 108 g(Nd)/a

Sedimentary dissolution: FBE = 1.1 1010 g(Nd)/a

800 - 5000 m

Nd

Nd

Data

Mod

el

[Nd]

After many sensitivity tests: synthesis(Arsouze, 2008; Arsouze et al, 2009)

Mod

el

800 - 5000 m

Nd

Model coupling OGCM and Nd cycle (all sources&sinks)(Arsouze, 2008; Arsouze et al, 2009)

.•BE is THE major source term (>95% of the total : 1.1 1010 g(Nd)/an).•Dust and dissolved river inputs significant in the Atlantic surface waters.•Reversible scavenging required in order to reconciliate the Nd and εNd with depth and along the thermohaline circulation •(in agreement with H. Elderfield and Ed Sholkovitz earlier hypothesis)

Continental inputs & margins: major role in the Nd oceanic cycle.…

And for the other chemical elements?