MET 112 Global Climate Change - Lecture 10
The Carbon Cycle (II)
Eugene Cordero
San Jose State University, Spring 2004
Outline
ƒ Carbon: Short term cycles
ƒ Carbon: Long term cycles
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The Long-Term Carbon Cycle – Inorganic
Component
Long-Term Carbon Cycle – Inorganic
Component
ƒ Organic compounds are produced by
–
ƒ Inorganic compounds are produced by
–
Atmosphere-Ocean-Biosphere
(CO2, dissolved CO2, organic
matter)
ƒ Slow exchange of carbon between the Earth’s crust and
the atmosphere-ocean-biosphere system.
ƒ Carbonates are
–
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Earth’s Crust
(carbonates)
3
Long-Term Carbon Cycle – Inorganic
Component
5
Destruction of Carbonates
ƒ Subduction
–
Atmosphere-Ocean-Biosphere
(CO2, dissolved CO2, organic
matter)
Creation of Carbonates
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ƒ Volcanism
–
Destruction of Carbonates
– CO2 rises to the surface with magma
–
Earth’s Crust
(carbonates)
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Subduction
Volcanic Eruption
Eruption injected
(Mt – megatons)
17 Mt SO2,
3 Mt Cl,
Mt. Pinatubo (June 15, 1991)
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MET 112 Global Climate Change
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Effect of Imbalances in the Long-Term
Carbon Cycle
The Long-Term Carbon Cycle
ƒ Imbalances in the long-term carbon cycle can
cause slow, but large, changes in atmospheric
CO2
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Long-Term Carbon Cycle (Quantitative
Assessment)
Effect of Imbalances
Atmosphere-Ocean-Biosphere
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AtmosphereOceanBiosphere
What would
happen?
Earth’s Crust
Carbon Content: 40, 000 Gt*.
Carbon Content: 40, 000, 000 Gt.
Earth’s Crust
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*1 Gt = 1015 grams
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Time Scale of Long-Term Carbon Cycle
Long-Term CO2 Changes
ƒ Suppose that a 1% imbalance developed
ƒ How long would it take to double the amount of
carbon in the atmosphere-ocean-biosphere?
Carbon Content: 40, 000 Gt.
0.0300
Gt./yr
Net Carbon Flux
Carbon Content: 40, 000, 000 Gt.
Answer:
Source: Berner, R. A., The rise of plants and their effect on
weathering and atmospheric
CO . Science, 276, 544-546.
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Effect on Climate
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The Short-Term Carbon Cycle
ƒ Slow changes in CO2 concentration would
cause slow changes in the Earth’s temperature
ƒ Geologic periods with high CO2 levels
–
ƒ Geologic periods with low CO2
–
ƒ Living plants remove CO2 from the atmosphere
by the process of
–
ƒ When dead plants decay, the CO2 is put back
into the atmosphere
–
ƒ However, some carbon escapes oxidation
when it is covered up by sediments
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Organic Carbon Burial Process
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Oxidation of Buried Organic Carbon
ƒ Eventually, buried organic carbon is exposed
by erosion
O2
ƒ The carbon is then oxidized to CO2
C
C
Some Carbon
escapes
oxidation
C
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The (Almost) Complete Long-Term Carbon
Cycle
Oxidation of Buried Organic Carbon
ƒ Inorganic Component
–
– Subduction/Volcanism
ƒ Organic Component
–
– Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon
(e.g., coal)
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The (Almost) Complete Long-Term
Carbon Cycle (Diagram)
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Reminder
ƒ Remember, these are very slow processes
Atmosphere (CO2)
Ocean (Dissolved CO2)
ƒ Time scale:
Biosphere (Organic Carbon)
Silicate-toCarbonate
Conversion
Carbonates
Organic
Carbon
Burial
Buried Organic Carbon
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Carbon cycle – inorganic/organic
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Fate of terrestrial carbon
ƒ Inorganic
– 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’
ƒ 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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ƒ Some transported by geologic cycles to the ocean.
ƒ Some is added to deposits that may be converted
to rock.
– Residence time in the rock cycle ~ 100K - 100M
yrs
ƒ Some carbon absorbed by plants through
photosynthesis escapes oxidation (respiration), is
buried, and may be transformed ultimately into
coal and oil.
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Carbon in the oceans
Carbon on land
ƒ Carbon in the soil
– is about twice that in the atmosphere,
ƒ Carbon in plants
– is about equal to that in the atmosphere
ƒ The flux of CO2 between land organisms and the
atmosphere is large
– ~ 15% of the total CO2 of the atmosphere is cycled
annually.
ƒ Average residence time of CO2
– in soils is 25-30 years,
– in the atmosphere 3 years, and
– in the oceans 1500 years.
ƒ CO2 dissolved in water is used in formation of
the shells and skeletons of marine organisms
(mostly CaCO3).
ƒ When organisms die, shells either dissolve or
are incorporated into marine sediments,
entering the rock cycle as sedimentary rocks
ƒ This process has created the planet’s largest
carbon reservoir - rocks
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The Carbon Silicate Cycle
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Changes in chemical weathering
ƒ About 80% of the CO2 exchanged between solid earth and
atmosphere
– uses the Carbon-Silicate cycle
ƒ Cycle very slow, ~ 0.5 billion yrs per cycle
ƒ CO2 dissolves in water to give carbonic acid
ƒ Acid causes erosion of the rocks which are mostly rich in
silicate
ƒ Weathering releases calcium and bicarbonate ions that
find their way to the sea
ƒ Marine organisms use those elements to form their shells
ƒ Dead marine organisms enter sedimentary rocks.
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ƒ 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)
ƒ 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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