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The Carbon Cycle

The Carbon Cycle. Carbon & Energy Metabolism Carbon & Human Energy Can Nature Compensate? The longer history of carbon. Final electron acceptor during oxidation of polysaccharide. 1. CARBON & ENERGY METABOLISM. (CH 2 O)n + O 2 CO 2 + H 2 O. aerobic respiration.

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The Carbon Cycle

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  1. The Carbon Cycle Carbon & Energy Metabolism Carbon & Human Energy Can Nature Compensate? The longer history of carbon

  2. Final electron acceptor during oxidation of polysaccharide 1. CARBON & ENERGY METABOLISM (CH2O)n + O2 CO2 + H2O aerobic respiration autotrophic photosynthesis Inorganic carbon source (autotrophs)

  3. The Carbon Cycle Energy Metabolism respiration photosynthesis

  4. Equilibrium – equal balance between any powers, influences, etc • What have fossil fuel emissions done to carbon equilibria in the atmosphere?

  5. 2. CARBON & HUMAN ENERGY • Respiration releases the most CO2 to the atmosphere. • What recent developments release lots of CO2 to the atmosphere?

  6. Fossil fuel consumption finishes what nature left undone millions of years ago respiration Not broken down by respiration

  7. Carbon & Human Energy(Hansen et al. 2000)

  8. US net carbon flux via land use changes: 1700-2000 • What does the overall trend show? (petagrams/yr = 1015 g) Here? Pre-1945: 27+ 6 pg released Post-1945: 2 + 2 pg sequestered What is happening here?

  9. Numbers are x1015 g

  10. 3.2 ≠ 5.2, so the equation is “missing” 2 billion tons of carbon each year.

  11. 3. CAN NATURE COMPENSATE FOR CO2? Greening Earth Society • Organization composed of electric utilities • Produced video: “The Greening of Planet Earth” • Rising CO2 levels will help to “green the planet” • Carbon dioxide from fossil fuels will be sequestered in plant biomass

  12. Photosynthesis – 6 CO2 + 6 H2O C6H12O6 + 6 O2 Note the carbon component  

  13. Net Primary Production (NPP) photosynthesis, minus respiration by the photosynthesizers (kg Carbon/m²/year ) • Gross Primary Production (GPP) – ? • Steady state ecosystem – GPP balanced by totalrespiration C6H12O6 + 6 O2 -------- 6 CO2 + 6 H2O 

  14. Question: What will happen to global NPP as tundra is converted to taiga?

  15. Table 1: Surface area by type of cover and total (from Atjay et al. 1979 and De Vooys 1979). Petagram = 1015 grams

  16. Will increased CO2 “green” the earth? a) Nutrients & veg growth Loblolly pine exposed to 1.5x higher CO2 Oren R, et al., Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere, NATURE 411: 469-472 ( 2001) Schlesinger WH, et al., Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO2  NATURE 411: 466-469 (2001)

  17. Free Air Carbon Enrichment (Duke University)

  18. Results: • Pines initially grew 25% faster • But, returned to normal growth after 3 years • Very little excess carbon sequestered in the soil litter • Growth rates increased 75% when nitrogen added. Conclusion: • Nutrients, not carbon, limit loblolly growth.

  19. b. Soil respiration CO2 enrichment causes – i. Short-termgrowth in European trees ii. Increasing soil microbial respiration iii. Declining sequestration of root-derived carbon in the soil • Implications? Heath J. et al., “Rising atmospheric CO2 reduces sequestration of root-derived soil carbon.” Science 309: 1711-1713 (2005)

  20. Other effects c) Alaskan white spruce growth is down due to drought stress (Barber et al. Nature 405:668) d) Climate change increases El Ninos, which cause droughts that lead to burning of tropical forests (Science 289:35)

  21. e) BUT, Rapid polar warming has promoted plant growth • From 1846-1995, lake freezes in Northern Hemisphere have diminished 12 days (Magnuson et al. Science 289: 1743) • Eurasian growing season is 18 days longer than in 1981 (J. Geophys. Res.) • Satellite photos: Northern Hemisphere vegetation denser now than 20 yr. ago (J. Geophys. Res.)

  22. NPP increased 7.1% in North America from 1982-1998 (based on satellite data) Hicke et al Geophys Res Let 29 (2002)

  23. About 50% of our increased CO2 emissions are being sequestered rather than accumulating in the atmosphere. • This rate is expected to diminish as warming reduces the capacity of ecosystems to sequester carbon.

  24. Compensation Puchlines #1. Increased NPP is occurring in northern polar regions and North America #2. In some areas / ecosystems it is limited by nutrients and countered by drought & fire. #3. Increased growth has not been a sink for all CO2

  25. Mauna Loa: atmospheric CO2 concentrations Why the sawtooth?

  26. 4. WHAT IS THE LONGER HISTORY OF CARBON?

  27. CO2 estimated using isotopic markers from marine algae – note big drop about 30 Mya Fig. from Stoll, Nature 441:579

  28. Even higher levels 450 Mya! >20X more CO2 than now So, why worry? Radiation of mammals x present concen.

  29. Greg Retallack, U of O: Why did atmospheric carbon diminish at end of Devonian? Hypothesis: • Development of large land plants • Roots caused soil to weather • Calcium and magnesium weathered from soil went to oceans & combined with dissolved sodium bicarbonate to form insoluble compounds. • Oceans absorbed more carbon from atmosphere.

  30. Image: Carbon Cycle Project, http://kfrserver.natur.cuni.cz/globe/index.html

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