marmara-vt results on core md04-2741

CEREGE - Marnaut Science meeting 22/01/2007

MARMARA-VT results on core MD04-2741

What tells us the pore fluid chemistry about past environment?

Work done by Guillaume Soulet during his Master training course at CEREGE (March- Sept. 2006)

Guillaume Soulet is now doing a PhD work between CEREGE (E. Bard) and IFREMER (Brest, G. Lericolais) focused on the geochemistry of Marmara and Black Sea sediments (+ pore waters in Black Sea)


MD01-2430MD04-2741

+ MD04-2770 in Black Sea


Correlation with 2430

CEREGE - Marnaut Science meeting 22/01/2007(CEREGE, Jan. 2005 )

Santorin eruption ~18 Kyr BP cal.

lacustrian-marine transition ~14.7/13.7 Kyr BP cal.

14C AMS on urchin: 9500 yrs BP cal.

av. accumulation rate ~ 40 cm/Kyr


GEOMAR sediment press(operated by G. Aloisi)

40 pore water samples

samples divided between CEREGE, PEPS-Lyon (G. Aloisi), and FU Berlin (M.

Tesmer)

very small water samples (3-15 ml)!


Measurements done at CEREGE:

• 18O and D on Finningan Delta Plus/dual inlet by equilibration (C. Vallet-Coulomb)

• chlorinity by capillary electrophoresis (G. Soulet)

• porosity by weight measur. of dried sediment samples (G. Soulet)


Oxygen-18 measurements (±0.04‰):

current marine deep

waters

lacustrian deep waters?

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

-6 -5 -4 -3 -2 -1 0 1 218 [‰ / ]O VSMOW

[ ]Depth cm

CEREGE PEPS


Deuterium measurements (±1‰):

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

-50 -40 -30 -20 -10 0 10 20 30 40

[‰ / ]D VSMOW

[ ]Depth cm

CEREGE PEPS


y = 6.7239x - 3.1879

R2 = 0.9826

-50

-40

-30

-20

-10

0

10

-6 -5 -4 -3 -2 -1 0 1 218 [‰ / ]O VSMOW

[‰ / ]D VSMOW

Isotope relationship: mixing line

lacustrian end-member

marine end-member

?


Chlorinity

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0 10 20 30 40 50Salinity

Depth [cm]

= 1.80655 • chlorinity

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0 5 10 15 20 25 30

Chlorinity

Depth [cm]

CEREGE FU Berlin


y = 2.4999x + 20.355

R2 = 0.8795

10

15

20

25

30

-6 -5 -4 -3 -2 -1 0 1 218 [‰ / ]O VSMOW

Chlorinity

Isotope relationship: mixing line

lacustrian end-member

marine end-member

?


Modelling:

* try to infer the lacustrian end-member

* advect & diffuse a tracer in the pore water

* test different hydrological scenarios

* use approximations like steady state compaction

* need several parameters > sensitivity tests


Modelling:

* advect & diffuse a tracer concentration C in the pore water

€

φ∂C∂t

= ∂∂z

φDeff∂C∂z

⎛

⎝ ⎜

⎞

⎠ ⎟−φU ∂C

∂z

where: is porosity

Deff is the effective diffusivity > need the tortuosity

U is advection due to sediment compaction


-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0.5 0.55 0.6 0.65 0.7 0.75 0.8

Porosity

Depth [cm]

Porosity = Vvoids/Vsample ≈ Vwater/Vsample


Porosity ≈ Vwater/Vsample = Mwater/(Mwater + Msed*water/sed)and assume sed = 2.85

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0.5 0.55 0.6 0.65 0.7 0.75 0.8

Porosity

Depth [cm]


Porosity and sedimentology

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0.5 0.6 0.7Porosity

Depth [cm]


Effective diffusivity:

Deff = D(T)/2(z)

where:

D(T) is the molecular diffusivity in water

(z) is the tortuosity of the sediment

Tortuosity: tests showed the profile is quite sensitive to the tortuosity > we use the recent Boudreau & Meysmann’06 model for clay, and apply a proportio-nality coefficient


Sensitivity tests to the effective diffusivity and porosity:d

ep

th [

m]

porosity

+ tortuosity: 2 = 1-n (Archie-type law)

n=


Sensitivity tests: relationship betw. the tortuosity and the lacustrian 18O


Sensitivity tests to different hydrological scenarios (18O and salinity history of deep waters): base scenario

mixing betw. Marmara lake and Egean sea

global 18O decrease of the ocean

current value

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

-15000 -10000 -5000 0

Age (cal. yrs BP)

18O


Sensitivity tests to different hydrological scenarios (18O and salinity history of deep waters): scenario à la Ryan

Black Sea outflow

current value

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

-15000 -10000 -5000 0

Age (cal. yrs BP)

18O

Y-D


Sensitivity tests to different hydrological scenarios (18O and salinity history of deep waters): scenario à la Aksu

Black Sea outflow

current value

Y-D-7

-6

-5

-4

-3

-2

-1

0

1

2

3

-15000 -10000 -5000 0

Age (cal. yrs BP)

18O

sapropel


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Best fit for the 3 scenarios: 18Olacus. ~ -7 ±.4‰ and Slacus.~ 5 ±2


Conclusion (1):

because the mixing is highly diffusive, the pore waters have forgotten details older than few Kyrs

(Péclet number: Pe = U.h/D ~ 10-3 )


steady state zone

transition zone

homogeneous zone

Conclusion (2):

top of the core not well modelled: origin of the 3 different zones?


steady state profile

Surficial mixing due to the tectonic?

seism: bubbling and mixing

diffusion towards a new steady state

profile

tracer

dept

h

Time


‘Ryan’ scenario + tectonic mixing 100 years ago:

What if periodic seisms had affected the profile?

dep

th

[m]

18O [‰]


‘Ryan’ scenario + tectonic mixing 3000 years ago:

> very small effect and only the last one may be felt

dep

th

[m]

18O [‰]

marmara-vt results on core md04-2741

Documents

different zones

steady state compaction

soulet porosity

steady state profilesurficial

pore waterwhere

molecular diffusivity

guillaume soulet

relationship betw