1. MET 112 Global Climate Change - Lecture 8
The Carbon Cycle
Eugene Cordero
San Jose State University
Outline
Earth system perspective
Carbon: what’s the big deal?
Carbon: exchanges
Long term carbon exchanges
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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
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4. An Earth System Perspective
Earth composed of:
These ‘Machines’ run the Earth
Holistic view of planet…
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5. An Earth System Perspective
Earth composed of:
Atmosphere
Hydrosphere
Cryosphere
Land Surfaces
Biosphere
These ‘Machines’ run the Earth
Holistic view of planet…
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6. The Earth’s history can be characterized by different geologic events or eras.

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Hydrosphere
Component comprising all liquid water
Surface and subterranean (ground water)
Thus…lakes, streams, rivers, oceans…
Oceans:
Oceans currently cover ~
Average depth of oceans:
Oceans store large amount of energy
Oceans dissolve carbon dioxide (more later)
Sea Level has varied significantly over Earth’s history
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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
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Cryosphere
Component comprising all ice
Antarctica, Greenland, Patagonia
Climate:
Typically high albedo surface
Positive feedback possibility (more later)
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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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Land Surfaces
Soils surfaces and vegetation
Climate:
Location of continents controls ocean/atmosphere circulations
Volcanoes return CO2 to atmosphere
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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
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Biosphere
All living organisms; (Biota)
Biota- "The living plants and animals of a region.“ or "The sum total of all organisms alive today”
Climate:
Photosynthetic process stores significant amount of carbon (from CO2);
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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)
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17. Some Interactions Between Components of Climate System
Hydrologic Cycle (Hydrosphere, Surface,and Atmosphere)
Evaporation from surface puts water vapor into atmosphere
Precipitation transfers water from atmosphere to surface
Cryosphere-Hydrosphere
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18. 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

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

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Interactions (cont)
Components of the Earth System are linked by various exchanges including
In this lecture, we are going to focus on the exchange of Carbon within the Earth System
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Interactions (cont)
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
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Carbon: what is it?
Carbon (C), the fourth most abundant element in the Universe,
Building block of life.
Carbon cycles through the land, ocean, atmosphere, and the Earth’s interior
Carbon found
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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.
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Carbon: where is it?
Exists:
Atmosphere:
Living biota (plants/animals)
Soils and Detritus
Carbon
Oceans
Most carbon in the deep ocean
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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
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Carbon conservation
Initial carbon present during Earth’s formation
Carbon is exchanged between different components of Earth System.
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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.
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The Carbon Cycle
The complex series of reactions by which carbon passes through the Earth's
Atmosphere
Carbon is exchanged in the earth system at all time scales
Short term cycle (from seconds to a few years)
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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)
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33. The carbon cycle has different speeds Short Term Carbon Cycle
Long Term Carbon Cycle

34. Short Term Carbon Cycle
One example of the short term carbon cycle involves plants
Photosynthesis:
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)
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35. 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 go down (slightly)
During fall: (more respiration)
atmospheric CO2 levels go up (slightly)
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37. Carbon exchange (short term)
Other examples of short term carbon exchanges include:
Soils and Detritus:
Surface Oceans
also release CO2
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38. 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
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40. Short Term Carbon Exchanges

41. Explain why CO2 concentrations goes up and down each year
In Class Question
Explain why CO2 concentrations goes up and down each year

42. Long Term Carbon Cycle

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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
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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
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45. 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
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46. Where is most of the carbon today?
Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as
Limestone is mainly made of calcium carbonate (CaCO3)
Carbonates are formed by a complex geochemical process called:
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47. 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)
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48. Silicate to carbonate conversion – chemical weathering
One component of the long term carbon cycle

49. Granite (A Silicate Rock)
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50. Limestone (A Carbonate Rock)
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51. Silicate-to-Carbonate Conversion
Chemical Weathering Phase
Carbonic acid dissolves silicate rock
Transport Phase
Formation Phase
In oceans, calcium carbonate precipitates out of solution and settles to the bottom
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52. 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
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53. Silicate-to-Carbonate Conversion
Rain
1. CO2 Dissolves in Rainwater
2. Acid Dissolves Silicates
3. Dissolved Material Transported to Oceans 4.
Land
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54. 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
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55. Changes in chemical weathering
The process is temperature dependant:
rate of evaporation of water is temperature dependant
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
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56. 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
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Earth vs. Venus
The amount of carbon in carbonate minerals (e.g., limestone) is approximately
On Earth, most of the CO2 produced is
On Venus, the silicate-to-carbonate conversion process apparently never took place
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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
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59. Subjuction/Volcanism
Another Component of the Long-Term Carbon Cycle

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Subduction
During this processes, extreme heat and pressure convert carbonate rocks eventually into CO2
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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
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Volcanic Eruption
Eruption injected
(Mt – megatons)
17 Mt SO2,
3 Mt Cl,
Mt. Pinatubo (June 15, 1991)
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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)
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64. Organic Carbon Burial/Oxidation of Buried Carbon
Another Component of the Long-Term Carbon Cycle

65. Buried organic carbon (1)
Living plants remove CO2 from the atmosphere by the process of
When dead plants decay, the CO2 is put back into the atmosphere
However, some carbon escapes oxidation when it is covered up by sediments
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66. 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
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67. Organic Carbon Burial Process
Some Carbon escapes oxidation C
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68. 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
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69. Oxidation of Buried Organic Carbon
Eventually, buried organic carbon may be exposed by erosion
The carbon is then oxidized to CO2
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70. Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon (e.g., coal)
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71. Oxidation of Buried Organic Carbon
Atmosphere
Erosion
Buried Carbon (e.g., coal)
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72. Oxidation of Buried Organic Carbon
Atmosphere
CO2 O2 C
Buried Carbon
Result: Carbon into atmosphere (CO2)
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73. The Long-Term Carbon Cycle
Inorganic Component
Subduction/Volcanism
Organic Component
Oxidation of Buried Organic Carbon
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74. 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
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75. The Long-Term Carbon Cycle (Diagram)
Atmosphere (CO2)
Ocean (Dissolved CO2)
Biosphere (Organic Carbon)
Silicate-to-Carbonate Conversion
Organic Carbon Burial
Carbonates
Buried Organic Carbon
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76. 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
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79. Review of Long Term Carbon Cycle
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80. 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
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81. 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
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82. 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
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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
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84. Activity (groups of two)
Imagine that the global temperature were to increase significantly for some reason.
How would the silicate-to-carbonate conversion process change during this warming period. Explain.
How would this affect atmospheric CO2 levels and as a result, global temperature?
What type of feedback process would this be and why (positive or negative)?
Three points for
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85. 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
0 of 5
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86. How would atmospheric CO2 levels change?
Increase
Decrease
Stay the same
Impossible to tell
0 of 5
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87. How would this affect global temps?
Increase
Decrease
Stay the same
Impossible to tell
0 of 5
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88. What type of feedback process would this be
Positive
Negative
Neither
Both
0 of 5
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89. Effect of Imbalances Atmosphere-Ocean-Biosphere What would happen?
Earth’s Crust
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90. Long term carbon cycle
If the carbon cycle was in balance, then the amount of carbon going into the Earth’s crust would equal the amount leaving
Atmosphere-Ocean-Biosphere
Earth’s Crust
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91. Effect of Imbalances Atmosphere-Ocean-Biosphere What would happen?
Imbalances in the long-term carbon cycle can cause slow, but sizeable changes in atmospheric CO2
Atmosphere-Ocean-Biosphere
What would happen?
Earth’s Crust
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92. Consider the long term carbon cycle as seen below
Suppose the Atmosphere-Ocean-Biosphere has 40,000 Gt* of carbon and the earth’s crust has 40,000,000 Gt of carbon
Atmosphere-Ocean-Biosphere
*1 Gt = 1015 grams
Earth’s Crust
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93. Atmosphere-Ocean-Biosphere
Suppose that an imbalance developed in which the amount leaving the Atm/Ocean/Biosphere was to decrease by 1%.
If the arrows represent flux (carbon moving), and flux from the Earth’s crust to the atm/ocean/bio (labeled B) is 0.03Gt/year, what would the flux be for arrow A?
Atmosphere-Ocean-Biosphere
40,000 Gt
*1 Gt = 1015 grams
Gt./yr A B
Earth’s Crust
40,000,000 Gt

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Arrow A would be
0.03 Gt/yr
0.3 Gt/yr
Gt/yr
Gt/yr
0 of 5
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95. Atmosphere-Ocean-Biosphere 40,000 Gt
For such an imbalance as shown below, what is the net carbon flux and in what direction?
Atmosphere-Ocean-Biosphere
40,000 Gt
*1 Gt = 1015 grams
Gt./yr
Gt./yr A B
Earth’s Crust 40,000,000 Gt
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96. MET 112 Global Climate Change
For such an imbalance as shown below, what is the net carbon flux and in what direction? up
0.033 down up
down
0 of 5
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97. Atmosphere-Ocean-Biosphere
Based on the below Carbon Flux information, how many years will it take for the carbon in the atm/ocean/bio to double?
*1 Gt = 1015 grams
Atmosphere-Ocean-Biosphere
40,000 Gt
Net Carbon Flux
Gt./yr
Gt./yr
Gt./yr A B
Earth’s Crust
40,000,000 Gt

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How many years will it take for the carbon in the atm/ocean/bio to double?
0.03 years
12 years
100,000 years
133 million years
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99. Atmosphere-Ocean-Biosphere
Based on the below Carbon Flux information, how many years will it take for the carbon in the atm/ocean/bio to double?
Answer: 40, 000/.0003 years = 133 million years
*1 Gt = 1015 grams
Atmosphere-Ocean-Biosphere
Net Carbon Flux
Gt./yr
Gt./yr
Gt./yr A B
Earth’s Crust

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Long-Term CO2 Changes
Source: Berner, R. A., The rise of plants and their effect on weathering and atmospheric CO2. Science, 276,
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101. Time Scale (Continued)
The preceding operation would remove 40, 000 Gt. of carbon from the crust;
This is only 0.1% of the carbon in the crust
Thus, it is perfectly plausible that such an imbalance could be sustained
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103. Carbon cycle – inorganic/organic
Carbon exists in the atmosphere (CO2, CH4) and many rocks (sedimentary)
CO2 is exchanged between the atmosphere and oceans by diffusion.
CO2 and water produces ‘chemical weathering’
Organic
Carbon enters biological cycle through photosynthesis
Carbon stored in the woody parts of vegetation, especially trees.
Carbon leaves the biological cycle through respiration.
Some carbon stored in organisms’ bodies or soil, rather than being released through respiration.
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Carbon in the oceans
CO2 dissolved in water is used in formation of the shells and skeletons of marine organisms (mostly CaCO3).
When organisms die, shells either dissolve or are incorporated into marine sediments, entering the rock cycle as sedimentary rocks
This process has created the planet’s largest carbon reservoir - rocks
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105. The Carbon Silicate Cycle
About 80% of the CO2 exchanged between solid earth and atmosphere
uses the Carbon-Silicate cycle
Cycle very slow, ~ 0.5 billion yrs per cycle
CO2 dissolves in water to give carbonic acid
Acid causes erosion of the rocks which are mostly rich in silicate
Weathering releases calcium and bicarbonate ions that find their way to the sea
Marine organisms use those elements to form their shells
Dead marine organisms enter sedimentary rocks.
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106. The Carbon Cycle
Air
Land/Ocean

107. Long-Term Carbon Cycle (Quantitative Assessment)
Carbon Content: 40, 000 Gt*.
Atmosphere-Ocean-Biosphere
Carbon Content: 40, 000, 000 Gt.
Earth’s Crust
*1 Gt = 1015 grams
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108. Long-Term Carbon Cycle (Quantitative Assessment)
Carbon Content: 40, 000 Gt*.
Atmosphere-Ocean-Biosphere
Carbon Flux: 0.03 Gt/yr
Carbon Flux: 0.03 Gt/yr
Carbon Content: 40, 000, 000 Gt.
Earth’s Crust
*1 Gt = 1015 grams
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109. Time Scale of Long-Term Carbon Cycle
Suppose that a 1% imbalance developed
How long would it take to double the amount of carbon in the atmosphere-ocean-biosphere?
Carbon Content: 40, 000 Gt.
Gt./yr
Net Carbon Flux
Carbon Content: 40, 000, 000 Gt.
130 million years
Answer:
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110. Time Scale of Long-Term Carbon Cycle
Suppose that a 1% imbalance developed
How long would it take to double the amount of carbon in the atmosphere-ocean-biosphere?
Carbon Content: 40, 000 Gt.
Gt./yr
0.0003
Gt./yr
Gt./yr
Net Carbon Flux
Carbon Content: 40, 000, 000 Gt.
130 million years
Answer: 40, 000/.0003 years = 133 million years
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111. The Carbon Cycle Short term (fast ~ 1-5 years)
Long term (thousands of years)
Short term (fast ~ 1-5 years)
Air
Land/Ocean