1 met 12 global climate change - lecture 7 the carbon cycle shaun tanner san jose state university...

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MET 12 Global Climate Change - Lecture 7

The Carbon CycleShaun 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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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

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

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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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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.

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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) 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)

Figure 4.13 Global carbon cycle

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 decays, carbon is mostly returned to the

atmosphere (respiration) During spring: (more photosynthesis)

During fall: (more respiration)

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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 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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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?)

CO2 levels are largest in this month

1. Jan

2. May

3. August

4. October

CO2 levels are lowest when

1. Plants are growing and take up more CO2

2. Plants are decaying and take up more CO2

3. Plants are growing and give off more CO2

4. Plants are decaying and give off more CO2

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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

Short Term Carbon Exchanges

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

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 rock

2. Transport Phase• Solution products transported to ocean by

rivers3. 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

Subduction/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

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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The Long-Term Carbon Cycle (Diagram)

Atmosphere (CO2)

Ocean (Dissolved CO2)

Biosphere (Organic Carbon)

Carbonates Buried Organic Carbon

Subduction/Volcanism

Silicate-to-Carbonate Conversion

Organic Carbon Burial

Oxidation of Buried Organic Carbon

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Review of Long Term Carbon Cycle

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Activity

Answer the following questions1. If volcanism was to increase, how would that affect

global temperatures?2. If oxidation of organic carbon was to increase, how

would that affect global temperatures?3. If there was a decline in the silicate to carbonate

process, how would that affect global temps?4. If volcanism was to increase, how would that affect

the rate of oxidation of buried carbon?5. If the earth warmed, how would that affect the

silicate to carbonate conversion process? What kind of feedback would this produce?

If volcanism was to increase over a period of thousands of years, how would this affect atmospheric CO2 levels?

Atmospheric CO2 levels would

1. Increase

2. Decrease

3. Stay the same

4. Are not related to volcanism

If the oxidation of organic carbon was to increase, how would global temperatures respond?

Global temperatures

1. Would increase

2. Would decrease

3. Would stay the same

4. 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

1. Would increase

2. Would decrease

3. Would stay the same

4. Are not 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

1. Increase

2. Decrease

3. Stay the same

4. Not be affected by the silicate to carbonate conversion process

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The silicate to carbonate conversion processes would

1. Increase

2. Decrease

3. Remain unchanged

4. Impossible to tell

Imagine that the global temperature were to increase significantly for some reason.

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How would atmospheric CO2 levels change?

1. Increase

2. Decrease

3. Stay the same

4. Impossible to tell

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What type of feedback process would this be

1. Positive

2. Negative

3. Neither

4. Both