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

%organic carbon Bottom water oxygen Primary productivity

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

No difference between sites with Low and high BW O 2

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

Does Oxygen matter? Evidence from turbidites Wilson et al.,1985 GCA 49,

Pore water concentration data Turbidite No turbidite

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

Almost all Corg burial in the ocean occurs on continental margins Hedges and Keil, 1995 Mar Chem 49,

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

Generalization to other margin areas Lines = relationship from >70m Gulf of Maine 0.57 mgOC/m 2

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

Confirmation of “monolayer equivalent concentration” observation S = sand sized L = silt C = clay After: 1)Subtracting discrete org particles 2)Correcting for interlamellar surface

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…

An experiment: does adsorption protect sedimentary organic matter from oxidation? In situ: Corg and SA closely relatedExperiment: 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

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

Oxic decomposition: an experimental approach Hulthe et al., 1998 GCA 62, 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)

Result Experimental data Result

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

The use of sedimentary data

Result… water column [O2] matters

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

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

Result

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