Long Term/Geological Carbon Cycle

Question 1

Describe the processes in the long-term carbon cycle.

Answer 1

1. Carbon dioxide in the atmosphere reacts with water vapour to form a weak carbonic acid - acid rain.
2. Carbonic acid reacts with carbonate rocks.
3. The carbonate ions are transported from rivers into the ocean.
4. Carbonate ions in oceans are used to form shells and exoskeletons of marine organisms.
5. When these organisms die, their carbonate shells are compacted and lithified, forming limestone.
6. Tectonic movement causes subduction of ocean floor material into the mantle, forming magma..
7. Volcanic eruptions release carbon dioxide into the atmosphere (outgassing) and lava, which solidifies, forming carbon-rich rocks.

It takes roughly 100-200 million years for a carbon atom to complete a full revolution of the long-term carbon cycle. (The fast term carbon cycle can take anywhere from hours to centuries)

Question 2

Carbon Stores

Answer 2

Lithosphere - This is the largest store of carbon, containing 99.9% of all carbon on Earth (Roughly 100,000,000 petagrams). A further 4000 petagrams are stored as fossil fuels

Hydrosphere - This is the second largest store of carbon, accounting for 0.0038% of the world’s carbon (roughly 38,000 petagrams). Mostly carbonate ions and dissolved carbon dioxide, which forms carbonic acid.

Pedosphere - Accounts for 0.00023% of the world’s carbon (roughly 2300 petagrams). Mostly peat (60% carbon). This is composed of dead matter in areas lacking oxygen, meaning slower decomposition.

Atmosphere - Accounts for 0.00017% of the world’s carbon (roughly 750 petagrams of carbon, however textbook states 560). Mostly as carbon dioxide and methane. There has been a 36% increase in atmospheric carbon in the last century.

Biosphere - Accounts for 0.00012% of the world’s carbon (roughly 560 petagrams)

1 petagram = 1 billion tonnes (1 gigatonne) or 1 trillion kg

Question 3

Flows of carbon.

Answer 3

Weathering and erosion (lithosphere to hydrosphere) - 0.8PgC per year
Sedimentation and Fossilisation (hydrosphere to lithosphere) - 0.2 PgC per year

Diffusion out of oceans (hydrosphere to atmosphere) - 90.3 PgC per year
Diffusion into oceans ( atmosphere to hydrosphere) - 92 PgC per year ( Oceans are a carbon sink)

Photosynthesis (atmosphere to biosphere) - 103 PgC per year
Respiration (biosphere to atmosphere) - 50 PgC per year (vegetation is a carbon sink)

Decomposition (biopshere to lithosphere) - 50 PgC per year