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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.