1. Introduction: Carbon Cycle
• Carbon isotopes have been very heavily utilized to study various aspects of the earth’s carbon cycle.
• Extremely diverse applications
-Global, regional and local scales
-Ocean, atmosphere, terrestrial environments
-Current, historic, geologic time scales
• Mainly CO2 cycle, but CH4 cycle also important.

2. Earth’s Carbon Cycle

3. Size and d13C of Earth’s Carbon Reservoirs

4. d13C in the Carbonate Rock Record

5. Equilibrium Fractionation effects for DIC (CO2aq, HCO3- and CO3=)

6. d13C of Fossil Fuels Consumed Globally
Natural gas ~ –44 ‰
Oil ~ –27 ‰
Coal ~ –24 ‰

7. d13C of Atmospheric CO2

8. d13C vs CO2 Concentration in Air

9. Current Atmospheric CO2 Budget
R. Feely (PMEL)

10. Decadal Change in the DIC and d13C in the surface waters of the subtropical N. Pacific
C.D. Keeling et al, in GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 18, GB4006, 2004.

11. S
d13C of plants

12. Seasonal Atmospheric CO2 and d13C

13. d13C of Seasonal Atmospheric CO2 Changes

14. Photosynthetic Pathways for C3 and C4 Plants

15. Photosynthetic Pathway for C3 Plants

16. Photosynthetic Pathway for C4 Plants

17. Fractionation Factors during Photosynthesis
α = Klight/Kheavy
Sensitivity of αnet to pCO2int

18. Two Step Photosynthesis Model in a Leaf
CO2
CO2aq
CO2ext
CO2int
C6H12O6
Inside Leaf
Air

19. Sensitivity of d13C of C4 plants to pCO2int/pCO2ext
d13Cplant=d13CCO2ext – a – (b4+b3*f – a)*pCO2int/pCO2ext

20. Altitude Effects on d13C of plants

21. Within Tree d13C Variations

22. Recycling of CO2 in the Forest

23. Plant d13C Fractionation Effect (predicted by ecosystem model)