1. Carbon Cycle: distribution and size of stores

2. Key background info:
Carbon is the 4th most common element in the universe.
The carbon cycle (like the water cycle) is a closed system.
It is made up of several sub-systems which are open systems which transfer carbon between them and in doing so, affect conditions for all life on Earth.
The geography of the living, and many non-living, features of the planet at any one period of the Earth’s history is largely a response to the state of carbon in its various sub-systems.

3. Carbon compounds
Carbon compounds may take a range of different chemical forms:
As gases: carbon dioxide and methane in the atmosphere, soils and oceans
As a solid: calcium carbonate in rocks, skeletons and shells of sea creatures
As liquids: carbonic acid and calcium bicarbonate.
Of these, we study carbon dioxide in most detail due to the links with climate change.

4. Carbon cycle
Carbon is stored on our planet in the following major sinks:
as organic molecules in living and dead organisms found in the biosphere
(2) as the gas carbon dioxide in the atmosphere
(3) in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk
(4) in the oceans (hydrosphere) as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms.

5. Amount in Billions of Metric Tons
Estimated size of carbon stores
Sink
Amount in Billions of Metric Tons
Lithosphere:
Marine Sediments and Sedimentary Rocks
Fossil Fuel Deposits
66,000,000 to 100,000,000
4000
Hydrosphere
38,000 to 40,000
Biosphere:
Terrestrial Plants
Soil Organic Matter
540 to 610
1500 to 1600
Atmosphere
578 (as of 1700) (as of 1999)

6. Carbon Cycle: distribution and size of stores
Lithosphere
Biosphere
Hydrosphere
Atmosphere

7. Lithosphere
Is by far the largest store of carbon on Earth. Carbon is locked into solid form in carbon-based rocks such as dolomite, limestone, chalk and is concentrated in stocks of fossilised organic remains (oil, gas and coal) and in organic-rich rocks where it is more dispersed (oil and gas shales).

8. Hydrosphere
Oceans cover 71% of the Earth’s surface. The oceans contain the 2nd largest quantity of carbon in both organic and inorganic forms. Much is dissolved CO₂ absorbed from the atmosphere, some is in organisms such as plankton, corals and shells, and much is in sediments on the seafloor containing both methane and carbon dioxide.

9. Biosphere
Carbon is extracted from the atmosphere and oceans and builds organic (living) structures which, when they reach the end of their life cycle, return it to the atmosphere or ocean as CO₂ and other gases, or decompose into the soil or ocean bed as carbon compounds.

10. Atmosphere
CO₂ makes up only 0.04% of the atmosphere but is the key component, along with sunlight and water, of photosynthesis of plants. It also reacts readily with water to form carbonic acid, resulting in rain that is naturally acidic. Methane is a compound of carbon and hydrogen (CH₄) and is produced by biological processes.