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Organic Carbon Preservation

Organic Carbon Preservation . Large-scale data compilations -- Do Corg Concentration and Accumulation Rate reflect overlying water productivity? preservation rate variations -- bottom water O2? Evidence from the deep-sea: turbidites The importance of continental margins

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Organic Carbon Preservation

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  1. Organic Carbon Preservation Large-scale data compilations -- Do Corg Concentration and Accumulation Rate reflect overlying water productivity? preservation rate variations -- bottom water O2? Evidence from the deep-sea: turbidites The importance of continental margins Mechanisms of organic carbon preservation in margin sediments Mineralogical control The role of oxygen

  2. %organic carbon Bottom water oxygen Primary productivity

  3. Note that there is a large-scale correspondence Between %Corg and Corg accumulation rate

  4. No difference between sites with Low and high BW O2

  5. Open shape = Corg ox rate by O2 Symbols = Corg ox rate by SO4 Same comparison: euxinc and Semi-euxinic sites Result ….

  6. Does Oxygen matter? Evidence from turbidites Wilson et al.,1985 GCA 49, 811-822

  7. Pore water concentration data Turbidite No turbidite

  8. Interpretation of pore water data Consumption of contemporary Corg Consumption of Corg in turbidite

  9. Almost all Corg burial in the ocean occurs oncontinental marginsHedges and Keil, 1995 Mar Chem 49, 81-115

  10. A relationship between sedimentary surface area and %CorgMayer (1994) GCA 58, 1271 Interpretation sorption protects Corg from enzymatic attack Observation

  11. Generalization to other margin areas Lines = relationship from >70m Gulf of Maine 0.57 mgOC/m2

  12. 2 additions to Mayer study: size separation study source of om vs fate

  13. Confirmation of “monolayer equivalent concentration” observation S = sand sized L = silt C = clay After: Subtracting discrete org particles Correcting for interlamellar surface

  14. A conundrum… Using N:C and dC-13 as source markers… There appears to be nearly complete replacement of adsorbed terrestrial Material by adsorbed marine organic matter…

  15. An experiment: does adsorption protect sedimentary organic matter from oxidation? In situ: Corg and SA closely related Experiment: desorb and Innoculate with SO bacteria Sorted by age inferred from depth” A<50yr, B~160, C~300, D~470 Extent of degradation depends on age Rate after desorption >> in situ degradation rate

  16. Exceptions to the “monolayer coverage” rule Low flux, high O2 Central Eq. Pac. Deltaic seds High flux, Low O2 Protection by sorption matters, but other factors …O2? … do too

  17. Oxic decomposition: an experimental approachHulthe et al., 1998 GCA 62, 1319-1328 Sediments from shallow-water, margin setting Incubate in the presence or absence of O2 Incubate sediments from surface samples (oxic layer) and deep samples (anoxic)

  18. Result Result Experimental data

  19. Oxygen and water-column decompositionDevol and Hartnett (2001) L&O 46, 1684-1690 Use sedimentary data to Infer Corg flux vs. water depth … Does water column [O2] matter?

  20. The use of sedimentary data

  21. Result… water column [O2] matters

  22. And sedimentary data agree with trap results Data: low-O2 Mexico margin Dotted line: J. Martin result - higher [O2], greater attenuation with water depth

  23. A refinement of “Oxygen matters” --oxygen exposure timeHartnett et al. (1998) Nature 391, 572-574 Another Washington/ Mexico margin study Washington: higher O2, productivity Mexico: low O2, lower productivity

  24. Result

  25. Organic C preservation 3 important factors: Overlying water productivity Protection by sorption to mineral surfaces link between continental erosion rates and Corg preservation Oxygen exposure link between atmospheric O2 and Corg burial

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