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

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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.

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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 (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.

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

18. Carbon conservation Initial carbon present during Earth’s formation
Carbon is exchanged between different components of Earth System.

19. 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.

20. 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)

21. Figure 4.13 Global carbon cycle
Bloom-Fig jpg

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

23. 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)

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 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)

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27. 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 27

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

29. 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

30. 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

31. Short Term Carbon Exchanges

32. Long Term Carbon Cycle

33. 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

34. 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)

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

36. Granite (A Silicate Rock)

37. Limestone (A Carbonate Rock)

38. 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

39. Silicate-to-Carbonate Conversion
Rain
1. CO2 Dissolves in Rainwater
2. Acid Dissolves Silicates
3. Dissolved Material Transported to Oceans 4.
Land

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

41. 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

42. Earth vs. Venus the same as the amount of carbon in Venus’ atmosphere
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

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

44. 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

45. 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)

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

47. 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

48. Organic Carbon Burial Process
Some Carbon escapes oxidation C

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

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

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

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

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

54. 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

55. 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

58. Review of Long Term Carbon Cycle

59. Activity Answer the following questions
If volcanism was to increase, how would that affect global temperatures?
If oxidation of organic carbon was to increase, how would that affect global temperatures?
If there was a decline in the silicate to carbonate process, how would that affect global temps?
If volcanism was to increase, how would that affect the rate of oxidation of buried carbon?
If the earth warmed, how would that affect the silicate to carbonate conversion process? What kind of feedback would this produce?
Three points for 59 59

60. Atmospheric CO2 levels would
If volcanism was to increase over a period of thousands of years, how would this affect atmospheric CO2 levels?
Atmospheric CO2 levels would
Increase
Decrease
Stay the same
Are not related to volcanism

61. Are not affected by the oxidation of organic carbon
If the oxidation of organic carbon was to increase, how would global temperatures respond?
Global temperatures
Would increase
Would decrease
Would stay the same
Are not affected by the oxidation of organic carbon

62. Are not affected by the silicate to carbonate conversion process
If there was a decline in the silicate to carbonate conversion process, how would global temperatures respond?
Global temperatures
Would increase
Would decrease
Would stay the same
Are not affected by the silicate to carbonate conversion process

63. Not be affected by the silicate to carbonate conversion process
If the silicate to carbonate conversion process was to increase over a period of millions of years, how would this affect volcanism?
Volcanism would
Increase
Decrease
Stay the same
Not be affected by the silicate to carbonate conversion process

64. The silicate to carbonate conversion processes would
Imagine that the global temperature were to increase significantly for some reason.
Increase
Decrease
Remain unchanged
Impossible to tell

65. How would atmospheric CO2 levels change?
Increase
Decrease
Stay the same
Impossible to tell

66. What type of feedback process would this be
Positive
Negative
Neither
Both