The carbon cycle

eg of carbon compounds - calcium carbonate (CaCO3) solid in rocks, shells, ocean.

    hydrocarbons - in sedimentary rocks   |    methane (CH4) - oceans, soil, atmosphere

source -  primary source (mantle) escaping at constructive/destructive plate boundaries

stores - sedimentary rocks - 100 million GtC (gigatonnes)

Anthropogenic CO2 - CO2 generated by human activety 

 Carbon is one of the most chemically diverse of all elements , 4th most abundant in universe

Sedimentary rocks - compressed deposits of earths material (long term carbon storage)

metamorphism - melting of rock with heat / pressure

The lithosphere: stored in inorganic: coal, oil, natural gas | organic: organic matter

      carbon in the lithosphere distributed between :

1. marine sediments/sedimentary rocks (100 million GtC) 

2. soil organic matter

3. fossil fuel deposits

The hydrosphere: total oceanic carbon = 40,000 GtC - THREE OCEANIC STORES:

Surface layer (euphotic zone) - sunlight penetrates , photosynthesis

Intermediate layer (twilight zone) - organic matter

Carbon rich sediments - dead organisms reach sea bed, decay releases CO2, turn to sedimentary rocks

The biosphere: - total sum of living matter

living vegetation - 20% of carbon in biosphere

soil storage, living biomass, decayed vegetation, soil humus (litter decomposition)

The atmosphere:

 before industrial revolution - 280GtC | now - 400GtC

The pedosphere:

soil layer - composed of millions of organisms & weathered rock. Carbon both non + organic

The cryosphere:

stores of water in solid form. Rising sea levels = positive feedback on rate of removal of glacial ice

Carbon source - release more carbon that is absorbed (reverse for carbon sink)

 Four major cycles of carbon:

fast organic carbon cycle: months-centuries. transported via organisms between atmosphere, biosphere and pedosphere

fast non-organic carbon cycle:ocean to atmopshere exchange of CO2

slow organic carbon cycle: hundreds/million of years - long term sequestration of organisms. Also terrestrial forests (eg. gas, oil, coal)

slow non-organic carbon cycle: transfer of carbon from atmosphere -> hydrosphere. Also sedimentary stores in lithosphere - recycled via tectonic movement.

The carbon cycle maintains a balance that prevents all of the earth's carbon from entering the atmosphere - keeping the earths temperature stable

Weathering of rocks on continents creates net sink of carbon in oceans

Chemical weathering of rocks by carbonic acid (CaCO3) produces carbonate in run off water

When organisms die, shells are lithified - forming limestone 

Fast carbon cycle

- Photosynthesis - phytoplankton in euphoric zone turn carbon into organic matter via photosynthesis                   CO2 + H20 -> C6H12O6 + 02

- Respiration - winter - increased CO2 concentration ( decrease in vegetation) increase CO2 concentration in summer       O2 + C6H12O6 -> energy + H20 + C02

- Decomposition - physical, chemical, biological mechanisms transforming organic matter into stable forms 

chemical - oxidation        |          biological - digestion via enzymes

Weathering - carbon takes 100-200 million years to move between rock, soil, ocean + hydrosphere.

1. Atmospheric carbon combines with water to form weak carbonic acid - falls as acid rain

2. the acid dissolves rocks, releasing ions - rivers carry ions to oceans

Carbon sequestration in oceans - where CO2 is removed from atmosphere & oceans to be held in solid / liquid form in long term store (Carbon capture and storage)

1. Calcium ions combine with bicarbonate ions forming calcium bicarbonate - absorbed by corals / organisms. Organisms secrete solid calcium carbonate.

2. Calcium ions react with carbonate in water - producing calcium carbonate (forming limestone)

Burial / compaction

sedimentary rocks hold organic carbon via compressed delayed organisms/mud/carbon

Volcanic activity - slow cycle returns to atmosphere via volcanoes

(destructive plate boundary) magma has silicate  - releasing CO2

(((volcanoes emit 130 metric tonnes of CO2 per year)))

Diffusion - slow carbon (ocean) where air meets water, CO2 diffuses into the atmosphere

In ocean, CO2 reacts with water molecules releasing hydrogen (ocean therefore more acidic)

The ocean now takes more carbon than it releases