Carbon cycle and energy security

What is the carbon cycle?

The movement of carbon from one sphere to another.

What are stores and fluxes?

Stores: where carbon is held.

Fluxes: transfer of carbon between stores.

What are the different carbon stores?

Atmosphere → carbion dioxide/methane

Hydrosphere → dissolved carbon dioxide

Lithosphere → carbonates in limestone + fossil fuels

Biosphere → living/dead organisms

Cryosphere → stored in permafrost

What is the difference between stores and sinks?

Stores → add carbon to the atmosphere

Sinks → remove carbon from the atmosphere

Where is carbon geologically?

• Centred on the significant carbon stores in rocks and sediment.

• Formation of sedimentary carbon rocks (limstone) in oceans.

• Carbon derived from plants and animals in shale/coal/ other rocks

What geological processes release carbon?

Chemical weathering → atmospheric carbon reacts with moisture to form carbonic acid, this falls as rain and dissolves surface minerals.

Volcanic outgassing → volcanic eruptions and earthquakes release carbon dioxide pockets within the crust.

What are the three carbon pumps?

Biological, carbon, and physical

How does the biological pump work?

• Phytoplankton carry out photosynthesis.

• Zooplankton eat the phytoplankton, with carbon moving through the marine food web.

• Marine organisms die and sink to the marine floor.

• Carbon becomes part of sediments, forming fossil fuels or carbonate rocks e.g. Dover White Cliffs

What is carbon sequestration?

The process by which carbon dioxide is removed from the atmosphere.

How do phytoplankton sequester carbon?

• Half of the world’s oxygen is sourced from phytoplankton within the sunlit surface sea layer.

• Releases the same amount of oxygenas all land plants, although their biomass is 100x smaller.

• Consume 10x more carbon dioxide anually than humans release by burning fossil fuels.

What is the carbonate pump?

• Marine organisms utilise calcium carbonate to make hard outer shells and inner skeletons.

• When they die and sink, the shells dissolve and carbon becomes part of deep ocean currents.

• Those that do not dissolve build up into limestone, e.g. White Cliffs of Dover.

How does the physical pump work?

• CO2 is absorbed by diffusion in the ocean surface.

• Downwelling → surface water sinks in cold, dense waters.

• Thermohaline circulation globally distributes carbon.

• Colder water absorbs more CO2.

• Upwelling → warmer water rises, releasin CO2 back to the surface.

What is thermohaline circulation?

• The global system of surface and deep ocean currents.

• Driven by differences in temperature and salinity.

• Responsible for circulating carbon.