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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.

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Presentation on theme: "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."— Presentation transcript:

1 CEREGE - Marnaut Science meeting 22/01/2007 MARMARA-VT results on core MD 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)

2 CEREGE - Marnaut Science meeting 22/01/2007 MD MD MD in Black Sea

3 CEREGE - Marnaut Science meeting 22/01/2007 Correlation with 2430

4 CEREGE - Marnaut Science meeting 22/01/2007 (CEREGE, Jan ) Santorin eruption ~18 Kyr BP cal. lacustrian-marine transition ~14.7/13.7 Kyr BP cal. 14 C AMS on urchin: 9500 yrs BP cal. av. accumulation rate ~ 40 cm/Kyr

5 CEREGE - Marnaut Science meeting 22/01/2007 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)!

6 CEREGE - Marnaut Science meeting 22/01/2007 Measurements done at CEREGE:  18 O 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)

7 CEREGE - Marnaut Science meeting 22/01/2007 Oxygen-18 measurements (±0.04‰): current marine deep waters lacustrian deep waters?

8 CEREGE - Marnaut Science meeting 22/01/2007 Deuterium measurements (±1‰):

9 CEREGE - Marnaut Science meeting 22/01/2007 Isotope relationship: mixing line lacustrian end-member marine end- member ?

10 CEREGE - Marnaut Science meeting 22/01/2007 Chlorinity = chlorinity

11 CEREGE - Marnaut Science meeting 22/01/2007 Isotope relationship: mixing line lacustrian end-member marine end- member ?

12 CEREGE - Marnaut Science meeting 22/01/2007 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

13 CEREGE - Marnaut Science meeting 22/01/2007 Modelling: * advect & diffuse a tracer concentration C in the pore water where:  is porosity D eff is the effective diffusivity > need the tortuosity U is advection due to sediment compaction

14 CEREGE - Marnaut Science meeting 22/01/2007 Porosity = V voids /V sample ≈ V water /V sample

15 CEREGE - Marnaut Science meeting 22/01/2007 Porosity ≈ V water /V sample = M water /(M water + M sed *  water /  sed ) and assume  sed = 2.85

16 CEREGE - Marnaut Science meeting 22/01/2007 Porosity and sedimentology

17 CEREGE - Marnaut Science meeting 22/01/2007 Effective diffusivity: D eff = 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

18 CEREGE - Marnaut Science meeting 22/01/2007 Sensitivity tests to the effective diffusivity and porosity: depth [m] porosity + tortuosity:  2 =  1-n (Archie-type law) n=

19 CEREGE - Marnaut Science meeting 22/01/2007 Sensitivity tests: relationship betw. the tortuosity and the lacustrian  18 O

20 CEREGE - Marnaut Science meeting 22/01/2007 Sensitivity tests to different hydrological scenarios (  18 O and salinity history of deep waters): base scenario mixing betw. Marmara lake and Egean sea global  18 O decrease of the ocean current value

21 CEREGE - Marnaut Science meeting 22/01/2007 Sensitivity tests to different hydrological scenarios (  18 O and salinity history of deep waters): scenario à la Ryan Black Sea outflow current value Y-D

22 CEREGE - Marnaut Science meeting 22/01/2007 Sensitivity tests to different hydrological scenarios (  18 O and salinity history of deep waters): scenario à la Aksu Black Sea outflow current value Y-Dsapropel

23 CEREGE - Marnaut Science meeting 22/01/2007

24 Best fit for the 3 scenarios:  18 O lacus. ~ -7 ±.4 ‰ and S lacus. ~ 5 ±2

25 CEREGE - Marnaut Science meeting 22/01/2007 Conclusion (1): because the mixing is highly diffusive, the pore waters have forgotten details older than few Kyrs (Péclet number: Pe = U.h/D ~ )

26 CEREGE - Marnaut Science meeting 22/01/2007 steady state zone transition zone homogeneous zone Conclusion (2): top of the core not well modelled: origin of the 3 different zones?

27 CEREGE - Marnaut Science meeting 22/01/2007 steady state profile Surficial mixing due to the tectonic? seism: bubbling and mixing diffusion towards a new steady state profile tracer depth Time

28 CEREGE - Marnaut Science meeting 22/01/2007 ‘Ryan’ scenario + tectonic mixing 100 years ago: What if periodic seisms had affected the profile? depth [m]  18 O [‰]

29 CEREGE - Marnaut Science meeting 22/01/2007 ‘Ryan’ scenario + tectonic mixing 3000 years ago: > very small effect and only the last one may be felt depth [m]  18 O [‰]


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