Carbon Isotopes - University of Miamimgg.rsmas.miami.edu/groups/sil/carbon isotopes.pdf · Carbon...
Transcript of Carbon Isotopes - University of Miamimgg.rsmas.miami.edu/groups/sil/carbon isotopes.pdf · Carbon...
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Carbon IsotopesCarbon Isotopes
The Basics
A Short Course VU March, 2009Peter Swart University of Miami
14N(n,p)14C
NomenclatureNomenclature
13C/12C Standard
13C/12CSample-1 x 1000
,del, or delta values are reported in /oo or parts per thousand or per milleo, , p p p p
Less 13C, values are negative or said to be light
Less 13C, values are positive or said to be heavy
Standard is PDB (Pee Dee Belemnite)V-PDB (Vienna Pee Dee Belemnite)
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Forms of Carbon• Primordial Carbon (324,000,000 1015 grams)
– Methane
– Graphite
– Diamond
– Other ??
• Carbonates (60,000,000 1015 grams)Ca bo ates (60,000,000 0 g a s)
• Reduced Carbon (15,000,000 1015 grams)– Gas
• Thermogenic
• Biogenic
– Solid• Bitumen
• Coal
Range of Carbon IsotopesPDB
Hoefs 1982
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Range of Carbon IsotopesPDB
Hoefs 1982
12CO2Photosynthesis
12CO2Respiration
13CO2
CO2+ RUBP = PGA (ε=27‰)
RUBISCO
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PhotosynthesisPhotosynthesis
Major fractionation step involves the utilization of CO2 by plants in the process of photosynthesis
RuBP= Ribulose bis-phosphateRUBISCO= Ribulose bis-phosphate carboxylasePGA=Phosphoglyceraldehye
RUBISCOCO2 + RuBP = PGA (= 1.027)
CO2Guard Cells(close to preserve moisture)
Epithelium
CO2
Photosynthesis
Palisade layer
Translocation
Carbon in plantsCarbon in plants
C-3 plants have been around for over 600 myrs. Comprise most plants other than grasses.C-4 plants only evolved in the
last 10 myrsAlgae and marine plants are
heavier than C-3 plants and therefore differences in the geological record are mainly terrestrial (-20 to -30 per mille) and marine (-10 to -20 per mille)
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OxidationCH2O + O2 = CO2 + H2O -20Sulfate reductionCH2O + SO4
2- = HS- + HCO3- -20
Diagenesis• Remineralization
2 4 3
MethanogenesisCH2O + CO2 = CH4 +CO2 -60 and +10
Thermogenic Production2CH2O = CH4 + CO2 -30
0‰
Atmosphere ~ -8‰
Carbonates (~-2 to +5‰)
3C
(o/ o
o)
Organic material -10 to -30‰C4, Shallow marine
C3
Thermogenic methane -30 to -40‰
Biogenic methane -50 to -70‰
13 C3
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CO2 (-7 )
-20 to -30
CO2 + H2O= CH2O
(-8) (H2CO3- (+1)HCO3- (+3) CO3)
-1 to+1
-20 to -30
CO3 + Ca = CaCO3CO2 + H2O= CH2O
Atmospheric
Total amount 750 (590)Isotopic Composition -7
Shallow Ocean
Total Amount 970Isotopic Composition +1
90
92Vegetation
Total amount 610Isotopic composition -25
121
60 60
0.6
5Fossil FuelTotal 5,000Isotopic -20
CarbonatesTotal 60,000,000Isotopic +1
Organic Material in Sedimentary RocksTotal 15,000,000Isotopic -20
Primordial CarbonTotal 324,000,000Isotopic -8
SoilsTotal 1580Isotopic Composition -25
Deep Ocean
Total Amount 38,000Isotopic Composition -1
60
0.6
Units in 1015 g
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Chemical Reactions
• CO2 + CaSiO3 = CaCO3 + SiO2
• CO2 + MgSiO3 = MgCO3 + SiO2
• CH2O + O2 = CO2 + H2O
The more CO2 in the atmosphere, the faster weathering occurs and the faster there is a draw down of CO2
There is extremely little CO2 in the atmosphere compared to that in the rocksWeathering of carbonate rocks has little effect as carbon is quickly returned to the reservoir
Carbon Isotope Forcing• Sea-Level
– High sea-level enhanced burial of organic material
– Low sea-level enhanced oxidation of organic material
• Anoxic Basins– Enhanced preservation of organic material
• High Rates of Organic Material Formation– High concentrations of oxygen leading to
enhanced oxidation of sulfur
– High rates of organic carbon oxidation
Barnola, J.-M., D. Raynaud, C. Lorius, and N.I. Barkov. 2003. Historical CO2 record from the Vostok ice core. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.
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Neftel, A., H. Friedli, E. Moor, H. Lötscher, H. Oeschger, U. Siegenthaler, and B. Stauffer. 1994. Historical CO2 record from the Siple Station ice core. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A
Suess Effect• The decrease in the 14C of
atmospheric CO2 as a result of the burning of fossil CO2
• The Suess effect is superimposed upon the addition of 14C as a result of the bomb test.
• Carbon 14 is produced in the atmosphere as a result of the interaction with the solar wind
• 14N(n,p)14C
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Suess Effect• Rate of production of C-14 is not
constant because of – Variation in the strength of solar wind
– Variation in the Earth’s magnetic field
– Anthropogenic• Bomb blasts
Atmospheric C-14 from Wellington
500
600
700
800
0
100
200
300
400
18-May-27 24-Jan-41 3-Oct-54 11-Jun-68 18-Feb-82 28-Oct-95 6-Jul-09
Date
C-1
4
Manning, M.R., D.C. Lowe, W.H. Melhuish, R.J. Sparks, G. Wallace, C.A.M. Brennninkmeijer, and R.C. McGill. 1990. The use of radiocarbon measurements in atmospheric studies. Radiocarbon 32:37-58.
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C-13 Suess Effect• Change in the 13C of the atmospheric
CO2 as a result of the addition of fossil CO2
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0 ‰
HCO3- +0.5 ‰
Aragonite -HCO3- (+2.7‰)
Calcite -HCO3- (+1.0‰)
(o/ o
o)
Relationship between Carbon Species
CO2 (atmosphere) -7.8 ‰
CO2 (dissolved) -8.8 ‰
13C
Romanek, C.S., Grossman, E.L. and Morse, J.W. 1992. Carbon isotopic fractionation in synthetic aragonite and calcite: effects of temperature and precipitation rate. Geochimica et Cosmochimica Acta, 56: 419-430.
C ‰
3
8CO3
HCO3
H2CO3
Based on fractionation factors from Romanek et al. (1992) (Zeebe and Wolf-Gladrow, 2002)
pH
13 C
-12
-7
-2
0 5 10
3.5
4
4.5
5
5.5
6
6.5
2,00013 C
‰
100,000
2
2.5
3
6 6.5 7 7.5 8 8.5 9
pH
400