met 112 global climate change - lecture 8 the carbon cycle dr. craig clements san josé state...
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MET 112 Global Climate Change - Lecture 8
The Carbon CycleDr. Craig Clements
San José State University
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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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An Earth System Perspective
Earth composed of:– Atmosphere– Hydrosphere– Cryosphere– Land Surfaces– Biosphere
These ‘Machines’ run the Earth
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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)
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– 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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Greenland Ice Cap 2008
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Greenland Ice Cap 2008
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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”– Marine– Terrestrial
Climate: Photosynthetic process store significant amount
of carbon (from CO2)
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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?
1. Atmosphere-Cryosphere
2. Atmosphere-Hydropshere
3. Hydrosphere-Cryosphere
4. Atmosphere-Biosphere
5. Hydrosphere-Biosphere
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When water from lakes and the ocean evaporates, which components of the earth system are interacting?
1. Land Surface – atmosphere
2. Hydrosphere-atmosphere
3. Hydrosphere-land surface
4. Crysophere-Atmosphere
5. Biosphere-Atmosphere
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The Earth’s history can be characterized by different geologic events or eras.
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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
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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:
–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
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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 – 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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The carbon cycle has different speeds
Short Term Carbon Cycle
Long Term Carbon Cycle
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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
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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)
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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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Short Term Carbon Exchanges
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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:
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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:1. Chemical weathering (or called: “silicate to
carbonate conversion process”)2. Volcanism/Subduction3. Organic carbon burial4. Oxidation of organic carbon
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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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Silicate to carbonate conversion – chemical
weathering
One component of the long term carbon cycle
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Granite (A Silicate Rock)
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Limestone (A Carbonate Rock)
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Silicate-to-Carbonate Conversion
1. Chemical Weathering Phase
• CO2 + rainwater carbonic acid
• Carbonic acid dissolves silicate rock2. Transport Phase
• Solution products transported to ocean by rivers
3. Formation Phase• In oceans, calcium carbonate precipitates
out of solution and settles to the bottom
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Silicate-to-Carbonate Conversion
Rain1. 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
Calcium carbonate
Land
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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– 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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Subjuction/Volcanism
Another Component of the Long-Term Carbon Cycle
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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
Mt. Pinatubo (June 15, 1991)
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
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Organic Carbon Burial/Oxidation of Buried Carbon
Another Component of the Long-Term Carbon Cycle
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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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Organic Carbon Burial Process
CO2 Removed by Photo-Synthesis
CO2 Put Into Atmosphere by Decay
CC
O2
Some Carbon escapes oxidation
C
Result: Carbon into land
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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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Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon (e.g., coal)
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Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon (e.g., coal)
Erosion
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Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon
O2
CO2
C
Result: Carbon into atmosphere (CO2)
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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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