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MARMARA-VT results on core MD04-2741

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)

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MARMARA-VT results on core MD04-2741

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  1. 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)

  2. MD01-2430 MD04-2741 + MD04-2770 in Black Sea

  3. Correlation with 2430

  4. 14C AMS on urchin: 9500 yrs BP cal. lacustrian-marine transition ~14.7/13.7 Kyr BP cal. Santorin eruption ~18 Kyr BP cal. (CEREGE, Jan. 2005 ) av. accumulation rate ~ 40 cm/Kyr

  5. 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. Measurements done at CEREGE: •d18O and dD 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. Oxygen-18 measurements (±0.04‰): current marine deep waters lacustrian deep waters?

  8. Deuterium measurements (±1‰):

  9. Isotope relationship: mixing line marine end-member lacustrian end-member ?

  10. Chlorinity = 1.80655 • chlorinity

  11. Isotope relationship: mixing line marine end-member lacustrian end-member ?

  12. 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. Modelling: * advect & diffuse a tracer concentration C in the pore water where:  is porosity Deff is the effective diffusivity > need the tortuosity U is advection due to sediment compaction

  14. Porosity = Vvoids/Vsample ≈ Vwater/Vsample

  15. Porosity ≈ Vwater/Vsample = Mwater/(Mwater + Msed*rwater/rsed) and assume rsed = 2.85

  16. Porosity and sedimentology

  17. 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

  18. Sensitivity tests to the effective diffusivity and porosity: porosity + tortuosity: 2 = 1-n (Archie-type law) n= depth [m]

  19. Sensitivity tests: relationship betw. the tortuosity and the lacustrian d18O

  20. Sensitivity tests to different hydrological scenarios (d18O and salinity history of deep waters): base scenario global d18O decrease of the ocean current value mixing betw. Marmara lake and Egean sea

  21. Sensitivity tests to different hydrological scenarios (d18O and salinity history of deep waters): scenario à la Ryan Black Sea outflow current value Y-D

  22. Sensitivity tests to different hydrological scenarios (d18O and salinity history of deep waters): scenario à la Aksu Black Sea outflow current value Y-D sapropel

  23. Best fit for the 3 scenarios: d18Olacus. ~ -7 ±.4‰ and Slacus.~ 5 ±2

  24. 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 )

  25. Conclusion (2): top of the core not well modelled: origin of the 3 different zones? homogeneous zone transition zone steady state zone

  26. Surficial mixing due to the tectonic? tracer depth steady state profile seism: bubbling and mixing diffusion towards a new steady state profile Time

  27. ‘Ryan’ scenario + tectonic mixing 100 years ago: depth [m] d18O [‰] What if periodic seisms had affected the profile?

  28. ‘Ryan’ scenario + tectonic mixing 3000 years ago: depth [m] d18O [‰] > very small effect and only the last one may be felt

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