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Longterm carbon cycle Keeling plots & Paleoclimate

Longterm carbon cycle Keeling plots & Paleoclimate. Gerrit Lohmann Carbon Course 6. February 2006 @PEP, University of Bremen, Germany. Atmospheric CO 2 measurements. Increase in CO 2 Seasonal cycle N-S gradient. d 13 C and [CO 2 ] for last 200 years

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Longterm carbon cycle Keeling plots & Paleoclimate

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  1. Longterm carbon cycleKeeling plots & Paleoclimate Gerrit Lohmann Carbon Course 6. February 2006 @PEP, University of Bremen, Germany

  2. Atmospheric CO2 measurements • Increase in CO2 • Seasonal cycle • N-S gradient

  3. d13C and [CO2] for last 200 years ice core bubbles, Antarctica -6 -7 -8 d13C Suess Effect progressive depletion of CO2 resulting from burning of isotopically light fossil fuels ~1.5‰ over last century 340 320 300 280 CO2 1220 // 1700 1800 1900 2000

  4. d13C of atmospheric CO2 What feature do they share and why? Why do they differ? Allison, C.E. et al., “TRENDS”, DOE, 2003.

  5. Seasonal cycle also in 13-C and 18-O NOAA/CMDL

  6. 13-C: Terrestrial and Marine Fractionation

  7. Terrestrial Biosphere • Fractionation: photo-synthetic fixation of carbon with organic matter being depleted in the heavy isotope (13-C more negative). • Simplified reaction  6CO2 + 6H2O -> C6H12O6 + 6O2

  8. C3: Photosynethesis Problem

  9. C3: Photosynethesis Problem • Rubisco will sometimes recognize oxygen as a substrate instead of CO2 Competes with the regular reaction, mostly in warm climates Temperature Useless compound

  10. C3: Photosynethesis Problem • Rubisco will sometimes recognize oxygen as a substrate instead of CO2 Competes with the regular reaction, mostly in warm climates Temperature 2) Plants living in arid climates have to close the pores in their leaves when it is particulalry dry Useless compound

  11. Solution: C4 Photosynthesis • Plants discovered a way to make the carbon dioxide concentration very high C4 plants still execute “Calvin” cycle, but: CO2 grabbing and carbon fixation in different cells Melvin Calvin Nobel Prize 1961. 14-CO2

  12. Carbon in the biosphere = Net primary production - Respiration - Fire or harvesting NPP= Difference between the rate that carbon enters and leaves the biosphere ~ solar energy

  13. 13C: identify the species involved in exchange processes Two reservoir system C2 = C0 + C1 d13C2 * C2 = d13C0 * C0 + d13C1 * C1 d13C2 = C0 (d13C0 – d13C1) * 1/C2 + d13C1 y = m * x + b linear equation between new d13C2 and 1/C2 d13C1 as y-axis intercept Isotopic fractionation C2 C0 background C1 Unknown reservoir

  14. Isotopic fractionation C2 C0 background C1 Unknown reservoir Respired carbon dioxide from canopy vegetation and soils is mixed by turbulence within the canopy air space

  15. Keeling plot (C.D.Keeling,1958) Pataki et al 2003 Atmos. CO2 d13C = -8 ‰Grass d13C = -12.5 ‰ Leaves d13C = -26 ‰ Two limitations: • 2 reservoir system • Fast process

  16. Keeling plot 2 Seasonal cycle in atm 13C, CO2 has its origin in the variability of the terrestrial biosphere (d13C0 ~ -25 o/oo)

  17. Fossil Fuel Emissions Atmospheric CO2 Budget Atmospheric Increase Land and Ocean Sinks How do we partition the carbon sink between land and ocean?

  18. Partitioning of fossil fuel CO2 uptake based on the relatively well known O2:CO2 stoichiometric relation of the different fuel types measurements O2 CO2 Keeling and Shertz, 1992

  19. Partitioning of fossil fuel CO2 uptake based on the relatively well known O2:CO2 stoichiometric relation of the different fuel types measurements photosynthesis and respiration Uptake by land and ocean is constrained by the known O2:CO2 stoichiometric ratio of these processes Keeling and Shertz, 1992

  20. The Carbon Cycle (short term) green = reservoir size (1015g, Gigatons) red = fluxes (Gt/yr) *NOTE: d13C always reported in PDB Reservoirs and fluxes from Schlesinger, 1991; d13C from Heimann & Maier-Reimer, 1996

  21. green = reservoir size (1015g, Gigatons) red = fluxes (Gt/yr) blue = C isotopic value *NOTE: d13C always reported in PDB Reservoirs and fluxes from Schlesinger, 1991; d13C from Heimann & Maier-Reimer, 1996

  22. Stable Isotope Measurements • 12C 98.89% • 13C 1.11% • Isotopic Composition () • 13C (‰) = [13C/12Csample/ 13C/12Cstandard -1] x 1000 • d13C ~ 13C/C

  23. 13C budget equations forland/ocean partitioning CO2 mass balance sources sinks Atm. fossil fuel, deforestation ocean, land ff def ao al

  24. 13CO2 mass balance

  25. 13C budget equations forland/ocean partitioning CO2 mass balance 13CO2 mass balance d/dt (Ca 13Ca ) = disequilibrium Model estimates -28 ‰ -25 ‰ 2‰ 18 ‰ (C3) Tans et al. 1993 Battle et al. 2000

  26. Isotopic Disequilibrium Francey et al. 1999 Fung et al. 1997 Fossil fuels are old C3 (light) photosynthesis – emissions induce a decline in d13C of atmospheric CO2 Disequilibria induce changes in the carbon-13 content of the atmosphere without accompanying changes in the total mass of carbon! Flux returned to the atmosphere is “heavier”

  27. Carbon Budget Net Atmospheric Change 2.6 Pg C yr-1 -28 1 13-carbon flux Fossil Fuel Combustion and Cement Manufacture 6.4 Pg C yr-1 -25 Deforestation 2.0 Pg C yr-1 1 Total carbon flux Still et al. 2003

  28. Carbon Budget – All C3 Unknowns are solid arrows! Net Atmospheric Change 2.6 Pg C yr-1 13-carbon flux Fossil Fuel Combustion and Cement Manufacture 6.4 Pg C yr-1 Terrestrial and Oceanic Isotopic Disequilibrium Deforestation 2.0 Pg C yr-1 Total carbon flux Still et al. 2003

  29. Carbon Budget – All C3 Unknowns are solid arrows! Net Atmospheric Change 2.6 Pg C yr-1 Net Ocean Sink 2.3 Pg C yr-1 -2 1 -18 Net Land Sink 3.5 Pg C yr-1 1 13-carbon flux Fossil Fuel Combustion and Cement Manufacture 6.4 Pg C yr-1 Terrestrial and Oceanic Isotopic Disequilibrium Deforestation 2.0 Pg C yr-1 Total carbon flux Still et al. 2003

  30. C4 C3 Suits et al. GBC

  31. Carbon Budget –77% C3, 23% C4 (dashed) C3 only (standard assumption) C3:C4 mix 13-carbon flux Net Land Sink increased with C4 ! Total carbon flux Still et al. 2003

  32. Carbon Reservoirs (Pg) Gt/Pg C Calcium carbonate (CaCO3, limestone, german „Kalkstein“) is the largest carbon reservoir It is linked to the carbonate-silicate cycle

  33. Long term inorganic carbon cycle Weathering occurs because rocks and minerals become exposed to physical and chemical conditions that differ from conditions under which they formed • Temperature, pressure, supply of water • Physical weathering: Fracturing, frost wedging, salt weathering, thermal expansion, fire, roots from higher plants, …

  34. Dissolution

  35. Chemical Weathering:Hydration & hydrolysis Hydration: Incorporation of water molecules into a minaral Soluble mineral Hydrolysis: Incorporation of H+ or OH- into a minaral

  36. Oxidation & reduction Can be used to weather onther minerals

  37. Deposition into the Sea

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