MET 112 Global Climate Change - Lecture 8

1. MET 112 Global Climate Change - Lecture 8 The Carbon Cycle Dr. Craig Clements San José State University Outline • Earth system perspective • Carbon: what’s the big deal? • Carbon: exchanges • Long term carbon exchanges MET 112 Global Climate Change

2. 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 MET 112 Global Climate Change

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4. An Earth System Perspective • Earth composed of: • Atmosphere • Hydrosphere • Cryosphere • Land Surfaces • Biosphere • These ‘Machines’ run the Earth MET 112 Global Climate Change

5. The Earth’s history can be characterized by different geologic events or eras. MET 112 Global Climate Change

6. Hydrosphere • Component comprising all liquid water • Surface and subterranean (ground water) • Fresh/Salt water • Thus…lakes, streams, rivers, oceans… • Oceans: • Oceans currently cover ~ 70% of earth • Average depth of oceans: 3.5 km • Oceans store large amount of energy • Oceans dissolve carbon dioxide (more later) • Circulation driven by wind systems • Sea Level has varied significantly over Earth’s history • Slow to heat up and cool down MET 112 Global Climate Change

7. 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. MET 112 Global Climate Change

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9. Land Surfaces • Continents • Soils surfaces and vegetation • Volcanoes • Climate: • Location of continents controls ocean/atmosphere circulations • Volcanoes return CO2 to atmosphere • Volcanic aerosols affect climate MET 112 Global Climate Change

10. Biosphere • All living organisms; (Biota) • Biota- "The living plants and animals of a region.“ or "The sum total of all organisms alive today” • Marine • Terrestrial • Climate: • Photosynthetic process store significant amount of carbon (from CO2) MET 112 Global Climate Change

11. Interactions Between Components of Earth System • Hydrologic Cycle (Hydrosphere, Surface,and Atmosphere) • Evaporation from surface puts water vapor into atmosphere • Precipitation transfers water from atmosphere to surface • Cryosphere-Hydrosphere • When glaciers and ice sheets shrink, sea level rises • When glaciers and ice sheets grow, sea level falls MET 112 Global Climate Change

12. 45 of 70 When ice sheets melt and thus sea levels rise, which components of the earth system are interacting? • Atmosphere-Cryosphere • Atmosphere-Hydropshere • Hydrosphere-Cryosphere • Atmosphere-Biosphere • Hydrosphere-Biosphere

13. 46 of 70 When water from lakes and the ocean evaporates, which components of the earth system are interacting? • Land Surface – atmosphere • Hydrosphere-atmosphere • Hydrosphere-land surface • Crysophere-Atmosphere • Biosphere-Atmosphere

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

15. Interactions • Components of the Earth System are linked by various exchanges including • Energy • Water (previous example) • Carbon • In this lecture, we are going to focus on the exchange of Carbon within the Earth System MET 112 Global Climate Change

16. 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 (bioshpere), 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 MET 112 Global Climate Change

17. 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 MET 112 Global Climate Change

18. 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. MET 112 Global Climate Change

19. The Carbon Cycle • The complex series of reactions by which carbon passes through the Earth's • Atmosphere • Land (biosphere and Earth’s crust) • 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) MET 112 Global Climate Change

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21. The carbon cycle has different speeds Short Term Carbon Cycle Long Term Carbon Cycle MET 112 Global Climate Change

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 decay, carbon is mostly returned to the atmosphere (respiration) • Global CO2 MET 112 Global Climate Change

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24. 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 decay, carbon is mostly returned to the atmosphere (respiration) • During spring: (more photosynthesis) • atmospheric CO2 levels go down (slightly) • During fall: (more respiration) • atmospheric CO2 levels go up (slightly) MET 112 Global Climate Change

25. 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 MET 112 Global Climate Change

26. Short Term Carbon Exchanges MET 112 Global Climate Change

27. 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: MET 112 Global Climate Change

28. 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 MET 112 Global Climate Change

29. 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 MET 112 Global Climate Change

30. Where is most of the carbon today? • Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as • Carbonates (containing carbon) • Limestone is mainly made of calcium carbonate (CaCO3) • Carbonates are formed by a complex geochemical process called: • Silicate-to-Carbonate Conversion (long term carbon cycle) MET 112 Global Climate Change

31. Silicate to carbonate conversion – chemical weathering One component of the long term carbon cycle MET 112 Global Climate Change

32. Granite (A Silicate Rock) MET 112 Global Climate Change

33. Limestone (A Carbonate Rock) MET 112 Global Climate Change

34. 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 MET 112 Global Climate Change

35. 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 MET 112 Global Climate Change

36. 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 MET 112 Global Climate Change

37. 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 MET 112 Global Climate Change

38. Subjuction/Volcanism Another Component of the Long-Term Carbon Cycle

39. 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 MET 112 Global Climate Change

40. 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) MET 112 Global Climate Change

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

42. 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 MET 112 Global Climate Change

43. 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 MET 112 Global Climate Change

44. Oxidation of Buried Organic Carbon • Eventually, buried organic carbon may be exposed by erosion • The carbon is then oxidized to CO2 MET 112 Global Climate Change

45. Oxidation of Buried Organic Carbon Atmosphere Buried Carbon (e.g., coal) MET 112 Global Climate Change

46. Oxidation of Buried Organic Carbon Atmosphere Erosion Buried Carbon (e.g., coal) MET 112 Global Climate Change

47. Oxidation of Buried Organic Carbon Atmosphere CO2 O2 C Buried Carbon Result: Carbon into atmosphere (CO2) MET 112 Global Climate Change

48. 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 MET 112 Global Climate Change

49. 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 MET 112 Global Climate Change

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