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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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Deines (1980)

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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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Trophic Effects

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Isotopes and Carbonate Equilibrium

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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

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Clumped IsotopesClumped Isotopes