Modeling the Geochemical Carbon Cycle

By: Robert A. Berner and

Antonio C. Lasaga

Presented by: Kristin Hepper

What is the Geochemical Carbon cycle?

• It is the transfer of carbon between sedimentary rocks

• Carbon Dioxide is the chief player

Why study the geochemical carbon cycle?

• Fossil-fuels = energy

• The consequences of fossil-fuel burning are astronomical

• Greenhouse effect

The Greenhouse Effect

• Swedish chemist Svante August Arrhenius, 1896

• Found that carbon dioxide allows short-wavelength solar radiation to penetrate the atmosphere, but traps this energy when it is reradiated by the earth at longer wavelengths

• Any current greenhouse warming is primarily due to the burning of fossil fuels

How does the carbon get out of the rocks?

-Chemical Weathering

It is the natural analogue to the burning of fossil fuels

Chemical Weathering

• Sedimentary rocks are attacked by acids (carbonic acid)

• Causes them to break down

• End result = 2 bicarbonate ions

What happens next?

• One goes into the atmosphere

• The second goes into the groundwater

• Marine organisms use the bicarbonate ions to construct their skeletons and shells

Finally…

• The organisms die

• Their bodies are deposited and eventually buried on the seafloor

Somewhere out to sea…

To sum up…

• Carbonic acid in the soil• Two bicarbonate ions

-one is transformed into carbon dioxide and goes into the atmosphere

-and the other is used by marine organisms eventually becoming sedimentary rock

Radiolarian chert at the Marin Headlands

How does the rest of the carbon get back up into the atmosphere?

It has to do with plate tectonics…

Specifically, volcanic eruptions and related phenomena

Subduction zones

• Degassing is the main mechanism

• It happens at mid ocean ridges as well

What did our authors Berner and Lasaga do?

• They used computer models to run the geochemical cycle backwards

• To calculate planetary carbon dioxide levels from the past

What did they find?

• Fluctuations of atmospheric carbon dioxide

• Time scale is in the millions of years

• They think that these changes rival the much quicker changes being caused today by humans

Remember…

• The geochemical cycle could not function without tectonics

• Tectonism and climate are intimately linked

Carbon dioxide has always influenced global temperature

and will continue to do soTherefore…

By better understanding where we have come from, we can better predict where we are

headed.