1. MET 112 Global Climate Change - Lecture 8
The Carbon Cycle
Dr. Craig Clements
San José State University

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

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

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

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

8. 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.

9. Greenland Ice Cap 2008

10. Greenland Ice Cap 2008

11. 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

12. 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)

13. 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

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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

15. 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
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16. The Earth’s history can be characterized by different geologic events or eras.

17. 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

18. 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

19. 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

20. 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.

21. 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)

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

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)
Global CO2

26. 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)

27. 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

28. Short Term Carbon Exchanges

29. 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:

30. 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

31. 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)

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 (carbonic acid)
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. Subjuction/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
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