MET 112 Global Climate Change - Lecture 9

The Carbon CycleDr. Craig Clements

San José State University

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

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

An Earth System Perspective

Earth composed of:– Atmosphere– Hydrosphere– Cryosphere– Land Surfaces– Biosphere

These ‘Machines’ run the Earth

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

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

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)

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

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

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

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

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.

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)

The carbon cycle has different speeds

Short Term Carbon Cycle

Long Term Carbon Cycle

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

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)

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

How do we measure the short-term CO2 cycle?

– To determine the ecosystem exchange of CO2 we must measure the flux of CO2 between the biosphere and atmosphere.

– These measurements are routine and there is a network of stations that measure CO2 fluxes around the world.

How do we measure the short-term CO2 cycle?

– Ecosystems ‘breathe’ CO2 in and out.

– To determine the ecosystem exchange of CO2 we must measure the flux of CO2 between the biosphere and atmosphere.

– These measurements are routine and there is a network of stations that measure CO2 fluxes around the world.

CO2 Flux: Ecosystem ‘Breathing’

CO2 Exchange

CO2 Flux: Ecosystem ‘Breathing’

Fast, 3-D Anemometer

Fast, CO2 sensor(ms-1)

(mg m-3)

CO2 Flux: Ecosystem ‘Breathing’

CO2 Flux:

CO2 (ρ)concentration

Vertical Velocity perturbation (w’)

2COcF w

Flux = Eddy Covariance

To measure: Need fast velocity and CO2 measurements!

=(ms-1) x (mg m-3) =mg m-2 s-1

CO2 Flux: Ecosystem ‘Breathing’

H.P. Schmid (2000)

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:

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)

Silicate to carbonate conversion – chemical

weathering

One component of the long term carbon cycle

Granite (A Silicate Rock)

Limestone (A Carbonate Rock)

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

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

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

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

Subjuction/Volcanism

Another Component of the Long-Term Carbon Cycle

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

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

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

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

Oxidation of Buried Organic Carbon

Eventually, buried organic carbon may be exposed by erosion

The carbon is then oxidized to CO2

Oxidation of Buried Organic Carbon

Atmosphere

Buried Carbon (e.g., coal)

Oxidation of Buried Organic Carbon

Atmosphere

Buried Carbon (e.g., coal)

Erosion

Oxidation of Buried Organic Carbon

Atmosphere

Buried Carbon

O2

CO2

C

Result: Carbon into atmosphere (CO2)

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