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www.priweb.org/ed/pgws/history/pennsylvania/pennsylvania.html

Oil

www.priweb.org/ed/pgws/history/pennsylvania/pennsylvania.html

Early common mistakes in the oil business

Oil

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Climate

More recent common mistakes in the oil business

Carbon preservation factor 1: carbonrich sediments underlay regionsof high water column productivity.High primary productivity leads to highercarbon flux leads to greater carbonburial (though unknown mechanisms)

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Hartnett et al. (1998) Nature v391, 572-574

pp on Mexican shelf < Washington shelf; sedimentation rates are similar; O2 is very different

Carbon preservation factor 2: low oxygen leads to higher carbon preservation

The effect of oxygen has been refined somewhat to adjust fordifferences in exposure time, which is related to sedimentation

rate (depth of O2 penetration/sedimentation rate) = OET

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Cellulose

Glucose

Acetic Acid

CO2

Cellulose

CO2

What are the potential mechanisms? Aerobic and anaerobic degradation

Carbon preservation factor 3: The effect of organic matter composition(depending on the composition of the OM it can be very reactive, sort of reactive,

or not reactive at all.

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If you want to understand why C is preserved in marinesediments, look at where it is buried….

Protection and preservation of C on mineral surfacesLarry Mayer and others reasoned that there is no such thing as a naked mineral

surface in seawater. Further, the amount of C that can be loaded onto a sediment particle is proportional to its surface area.

weathering adsorption

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Organic carbon vs surface area for sediments fromthe Gulf of Maine

Organic carbon vs surface area for sediments fromthe Gulf of Maine

m = 0.57 mg C m-2

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Organic carbon vs surface area for sediments fromthe Gulf of Maine

m = 0.57 mg C m-2

Monolayer equivalent (ME) loading

Surfaces are coated with organicmatter to the equivalent of one molecule thick…

Sediments may be overloaded with C due to biogeochemicalcycling, but eventually diagenesis will reduce the C load to a set

surface area vs %OC value

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Mineral surface area vs %organic carbon for Columbia River Sediments(Hedges and Keil, Mar. Chem (1995) 49, 81-115.)

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Surface area vs %organic carbon for sediments from lowoxygen depositional regimes

m = 2.5 mg C m-2

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Surface area vs % organic carbon forEquatorial Pacific sediments

0.05 mg C m-2

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enzymes

Proposed mechanism for surface protectionadsorption of organic matter into very small pores

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Surface area control on OC preservation in marine sediment..

Weathering introduces new mineral surfaces constantly to the environment.

These surfaces ultimately become coated with organic matter, at approximatelya monolayer equivalent loading.

Under conditions that are typical for sediment deposition on continentalmargins (where most C is buried) degradation proceeds to the ME loadingand slows sufficiently there after to preserve this amount of carbon.

In open ocean setting, where oxygen exposure times are much longer, degradation proceeds to < ME loadings. In anoxic basins, where oxygen exposure times are much shorter, loadings are > ME.

Mechanism is preservation in small pores that are inaccessible to enzymes.e.g. physical protection.

From the small changes in the 13CNMR spectra of sinkingPOM, Hedges et al. infer that the C degradation actsnon-selectively, and that preservation occurs via physical protection.

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Is this evidence for or against physical protection ?

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But there is the problem with this model…

……think of the δ13C of marine sediments.

weathering adsorption

Surface area vs % organic carbonfor deltaic and river sediments

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Loss and replacement of terrestrial organic carbon fromriverine POM

Keil et al. 1997 GCA 61 1507-1511

Theoretical surface area of a 1 mm pitted spherical particleThe rebuttal to surface area control on OC preservation……

It is impossible to physically protect that much organic matter in pits & cracks

Ransom et al., GCA (1998) 62, 1329-1345

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Effect of high surface area material on total surface areaRansom et al., GCA (1998) 62, 1329-1345

Mineral surface area vs %organic carbon for Columbia River Sediments(Hedges and Keil, Mar. Chem (1995) 49, 81-115.)

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Grain size, smectite, opal, and surface area inWashington margin sediments

Ransom et al., GCA (1998) 62, 1329-1345

Correlation of surface area, TOC,Clay minerals+opal in Washington margin sediments

Ransom et al., GCA (1998) 62, 1329-1345

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…..and finally the mechanism of preservation….

Mayer-Hedges-Keil hypothesis Ransom hypothesis

Physical protection from enzymatic degradation in

small pores/cracks

No physical protectionOM is on surface and only

a small fraction is in contactwith mineral.

Photographic and experimental evidence shows that organic matter coatingonto particles was not even close to an even coverage, that OM is isolated

at very specific sites in blobs or blebs

Larry Mayer

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TOC vs surface are for California margin sedimentsRansom et al., GCA (1998) 62, 1329-1345

Correlation of clay minerals with TOCin coastal sediments

Ransom et al., GCA (1998) 62, 1329-1345

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Correlation of clay minerals with TOCin coastal sediments

Semectite rich clays

Chlorite rich clay

SLO clays21-29% smectite

0-3% chlorite

NM clays3-13% smectite13-24% chlorite

Clay mineralogy, not simple surface areadrives OC preservation

Semectite rich clays

Chlorite rich clay

Ransom et al., GCA (1998) 62, 1329-1345

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Things to remember…..

Most OM is preserved in continental margin sediments

Carbon loading is proportional to surface area

Sedimentation rate, or rate of burial may be a factor

Oxygen may be a factor

Minerology looks to be very important

The “mechanisms” of carbon preservation are still not understood. Many relationshipsbetween %C, sedimentation rate, SA, oxygen, have been shown, but we do not have a

mechanistic explanation for why these relationships are observed.

Tabulation of C burial in marine sediments

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Mineral surface area and % OC in suspended particulate organic matterand deltaic sediments of the Amazon River

Suspended particulate matter

Deltaic particulate matter Keil et al. 1997 GCA 61 1507-1511

What are the mechanisms of C preservation?

Primary production: The higher PP, the higher the flux of OM, the morerapidly the C/N/P transits the “reactive” zone of active C degradation.

Oxygen: Anaerobic systems require microbial consortia to degrade OMthat are inherently less efficient than aerobic organisms. Low oxygen limitsthe presence of aerobic respiration thereby preserving C. Longer initialpreservation, or other factors may lead to more extensive“geopolymerization” that more permanently preserves C.

There are intrinsically labile and non-labile structures of biomolecules. Themix of these will affect the amount of C preserved.

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Surface area vs %TOC in Washington margin sediments(Keil et al, (1994) GCA, 58, 879-893.