MET 12 Global Climate Change - Lecture 7

1. MET 12 Global Climate Change - Lecture 7 The Carbon Cycle Shaun Tanner San Jose State University Outline • Earth system perspective • Carbon: what’s the big deal? • Carbon: exchanges • Long term carbon exchanges

2. 2

3. 3

4. 4

5. 5

6. 6

7. 7

9. Goals • We want to understand the difference between short term and long term carbon cycle • We want to understand the main components of the long term carbon cycle

10. An Earth System Perspective • Earth composed of: • Atmosphere • Hydrosphere • Cryosphere • Land Surfaces • Biosphere • These ‘Machines’ run the Earth

11. The Earth’s history can be characterized by different geologic events or eras.

12. Cryosphere • Component comprising all ice • Glaciers, • Ice sheets: • Antarctica, Greenland, Patagonia • Sea Ice, Snow Fields • Climate: • Typically high albedo surface • Positive feedback possibility store large amounts of water; sea level variations.

15. Carbon: what is it? • Carbon (C), the fourth most abundant element in the Universe, • Building block of life. • from fossil fuels and DNA • Carbon cycles through the land (biosphere), ocean, atmosphere, and the Earth’s interior • Carbon found • in all living things, • in the atmosphere, • in the layers of limestone sediment on the ocean floor, • in fossil fuels like coal.

16. Carbon: where is it? • Exists: • Atmosphere: • CO2 and CH4 (to lesser extent) • Living biota (plants/animals) • Carbon • Soils and Detritus • Carbon • Methane • Oceans • Dissolved CO2 • Most carbon in the deep ocean

17. Carbon conservation • Initial carbon present during Earth’s formation • Carbon doesn’t increase or decrease globally • Carbon is exchanged between different components of Earth System.

18. The Carbon Cycle • The complex series of reactions by which carbon passes through the Earth's • Atmosphere,Land (biosphere and Earth’s crust) and Oceans • Carbon is exchanged in the earth system at all time scales • Long term cycle (hundreds to millions of years) • Short term cycle (from seconds to a few years)

19. Figure 4.13 Global carbon cycle

20. The carbon cycle has different speeds Short Term Carbon Cycle Long Term Carbon Cycle

21. Short Term Carbon Cycle • One example of the short term carbon cycle involves plants • Photosynthesis: is the conversion of carbon dioxide and water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product. • Plants require • Sunlight, water and carbon, (from CO2 in atmosphere or ocean) to produce carbohydrates (food) to grow. • When plants decays, carbon is mostly returned to the atmosphere (respiration) • During spring: (more photosynthesis) • During fall: (more respiration)

22. Short Term Carbon Cycle • One example of the short term carbon cycle involves plants • Photosynthesis: is the conversion of carbon dioxide and water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product. • Plants require • Sunlight, water and carbon, (from CO2 in atmosphere or ocean) to produce carbohydrates (food) to grow. • When plants decays, carbon is mostly returned to the atmosphere (respiration) • During spring: (more photosynthesis) • atmospheric CO2 levels start to go down (slightly) • During fall: (more respiration) • atmospheric CO2 levels start to go up (slightly)

23. 25

25. Question • What months are CO2 highest and lowest? • Explain the factors that contribute to the annual cycle in CO2 emissions. (Why do CO2 levels go up and down?) 27

26. CO2 levels are largest in this month Jan May August October 44 of 54

27. CO2 levels are lowest when Plants are growing and take up more CO2 Plants are decaying and take up more CO2 Plants are growing and give off more CO2 Plants are decaying and give off more CO2 46 of 54

28. Carbon exchange (short term) • Other examples of short term carbon exchanges include: • Soils and Detritus: • organic matter decays and releases carbon • Surface Oceans • absorb CO2 via photosynthesis • also release CO2

29. Short Term Carbon Exchanges

30. Long Term Carbon Cycle

31. Long Term Carbon Cycle • Carbon is slowly and continuously being transported around our earth system. • Between atmosphere/ocean/biosphere • And the Earth’s crust (rocks like limestone) • The main components to the long term carbon cycle: • Chemical weathering (or called: “silicate to carbonate conversion process”) • Volcanism/Subduction • Organic carbon burial • Oxidation of organic carbon

32. Silicate to carbonate conversion – chemical weathering One component of the long term carbon cycle

33. Granite (A Silicate Rock)

34. Limestone (A Carbonate Rock)

35. Silicate-to-Carbonate Conversion • Chemical Weathering Phase • CO2 + rainwater  carbonic acid • Carbonic acid dissolves silicate rock • Transport Phase • Solution products transported to ocean by rivers • Formation Phase • In oceans, calcium carbonate precipitates out of solution and settles to the bottom

36. Silicate-to-Carbonate Conversion Rain 1. CO2 Dissolves in Rainwater 2. Acid Dissolves Silicates (carbonicacid) 3. Dissolved Material Transported to Oceans 4. CaCO3 Forms in Ocean and Settles to the Bottom Land Calcium carbonate

37. Changes in chemical weathering • The process is temperature dependant: • rate of evaporation of water is temperature dependant • so, increasing temperature increases weathering (more water vapor, more clouds, more rain) • Thus as CO2 in the atmosphere rises, the planet warms. Evaporation increases, thus the flow of carbon into the rock cycle increases removing CO2 from the atmosphere and lowering the planet’s temperature • Negative feedback

38. Earth vs. Venus • The amount of carbon in carbonate minerals (e.g., limestone) is approximately • the same as the amount of carbon in Venus’ atmosphere • On Earth, most of the CO2 produced is • now “locked up” in the carbonates • On Venus, the silicate-to-carbonate conversion process apparently never took place

39. Subduction/Volcanism Another Component of the Long-Term Carbon Cycle

40. Subduction Definition: The process of the ocean plate descending beneath the continental plate. During this processes, extreme heat and pressure convert carbonate rocks eventually into CO2

41. Volcanic Eruption Eruption injected (Mt – megatons) 17 Mt SO2, 42 Mt CO2, 3 Mt Cl, 491 Mt H2O Can inject large amounts of CO2 into the atmosphere Mt. Pinatubo (June 15, 1991)

42. Organic Carbon Burial/Oxidation of Buried Carbon Another Component of the Long-Term Carbon Cycle

43. Buried organic carbon (1) • Living plants remove CO2 from the atmosphere by the process of • photosynthesis • When dead plants decay, the CO2 is put back into the atmosphere • fairly quickly when the carbon in the plants is oxidized • However, some carbon escapes oxidation when it is covered up by sediments

44. Organic Carbon Burial Process O2 CO2 Removed by Photo-Synthesis CO2 Put Into Atmosphere by Decay C C Some Carbon escapes oxidation C Result: Carbon into land

45. Oxidation of Buried Organic Carbon • Eventually, buried organic carbon may be exposed by erosion • The carbon is then oxidized to CO2

46. Oxidation of Buried Organic Carbon Atmosphere Buried Carbon (e.g., coal)

47. Oxidation of Buried Organic Carbon Atmosphere Erosion Buried Carbon (e.g., coal)

48. Oxidation of Buried Organic Carbon Atmosphere CO2 O2 C Buried Carbon Result: Carbon into atmosphere (CO2)

49. The (Almost) Complete Long-Term Carbon Cycle • Inorganic Component • Silicate-to-Carbonate Conversion • Subduction/Volcanism • Organic Component • Organic Carbon Burial • Oxidation of Buried Organic Carbon

50. The Long-Term Carbon Cycle (Diagram) Atmosphere (CO2) Ocean (Dissolved CO2) Biosphere (Organic Carbon) Subduction/Volcanism Oxidation of Buried Organic Carbon Silicate-to-Carbonate Conversion Organic Carbon Burial Carbonates Buried Organic Carbon