6.1 carbon and the geological cycle (EQ1)

Question 1

What is the Carbon Cycle?

Answer 1

Bio-geochemical cycle where carbon is stored and moved between spheres (atmosphere, hydrosphere, lithosphere and biosphere) through flows/ fluxes. It operates as a closed system but made up of interlinked subsystems which are open and have inputs and outputs.

• stores can add carbon to the atmosphere (SOURCE) and remove it (SINKS)

Question 2

a) types of stores

Answer 2

carbon exists in different forms depending on the store:

1. Atmosphere (smallest -0.0007%)
   - stored as CO2
2. Lithosphere (largest -99.96%)
   - stored in soil, as carbonate in limestones chalk and fossil fuels
3. Biosphere
   - stored as carbon atoms in living and dead organisms (plants and animals)
4. Hydrosphere
   - stored as dissolved CO2 in oceans

These stores vary in SIZE, CAPACITY & LOCATIONS.
((((the biosphere contains both terrestrial and oceanic locations))))

Question 3

a) what are fluxes + types of flux

Answer 3

(Fluxes/ flows are the movement of carbon from one store to another: inputs carbon and outputs it)
(((((they are measured in either petagrams or gigatonnes of carbon per yr.)))))

TYPES (highest to lowest flux of carbon per yr)
- Photosynthesis
- Diffusion in and out of oceans
- Respiration
- Decomposition
- Volcanic out- gassing
- Weathering & Fossilisation/ sedimentation

Question 4

Where is most carbon in the world stored?

Answer 4

GEOLOGICAL in rocks!!

the largest carbon store is geological- there is over 100 million Pg of carbon in the lithosphere!

Question 5

geological carbon cycle (formation of carbon stores: sedimentary rocks & limestone)

Answer 5

(((SLOWEST CYCLE AT A MINIMUM TURNOVER RATE OF 100,000 YRS)))

Formation of Sedimentary Rocks:
- sediment is deposited in layers in a low-energy environment (lake/ sea bed etc)
- further layers are deposited, lower layers become compressed and chemical reactions cement particles together.
the process of loose unconsolidated sediment into solid rock is known as LITHIFICATION!!!

Limestone:
(80% of lithospheric carbon is found in limestones)
Limestone is formed when calcium carbonate is deposited on the ocean floor, derived from plants and animals in shale coal and other rocks.
- when animals die their shells fall, sink and are deposited on the sea/ river floor.
- they are covered in mud/ silt and as a consequence decayed anaerobically and compressed further
- they undergo lithification which turns them into limestone (over hundreds of thousands of years/ millions!)

Question 6

geological carbon cycle (processes that release carbon: weathering and outgassing)

Answer 6

geological carbon can also be released into the atmosphere through geological PROCESSES.

chemical weathering:
- CO2 reacts with moisture to form carbonic acid
- this falls as acid rain where it reacts with some surface geology/minerals and slowly dissolves them. (eg limestone and chalk)

outgassing:
!release of gas previously trapped in some material!
- pockets of CO2 exist in the earths crust- volcanic eruptions and earthquakes can release this gas. occurs mainly along mid ocean ridges, subduction zones and at magma hotspots

(in more detail)
lithification (/fossilisation) on the sea floor creates carbonate rock which moves along with the oceanic plate until it subducts- subduction of carbonate rock at destructive plate boundaries: this gas then exists within the mantle and is released back through a composite cone volcano (volcanic outgassing)