T4.3:Carbon Cycling

the 4 spheres

biosphere

lithosphere

atmosphere

hydrosphere

the carbon cycle

biogeochemical cycle whereby carbon is exchanged between the different spheres of the Earth

how is carbon exchanged in the atmosphere

mainly as co2 and methane

how is carbon exchanged in the hydrosphere

bicarbonates dissolved in the water and calcium carbonate in corals and shells

how is carbon exchanged in living organisms

 carbohydrates, lipids and proteins found in all living things

how is carbon exchanged in non living remains

detritus and fossil fuels

how do autotrophs convert inorganic carbon dioxide into organic compounds

photosynthesis

example of organic compounds

carbohydrates, proteins,

what should levels of co2 in autotrophs be?

* should always be at a higher concentration in the atmosphere (or water)
* This concentration gradient ensures that carbon dioxide will passively diffuse into the autotrophic organism as required
* In aquatic producers, CO2 can usually diffuse directly into the autotroph; whereas in terrestrial plants, diffusion occurs at stomata
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compensation point

he uptake of CO2 by photosynthesis may at times be balanced by the production of CO2 by respiration

(net carbon assimuplation=0)

more net respiration than overall photosynthesis occuring=

atmospheric carbon dioxide levels should increase

what does carbon dioxide dissolve in water too

will combine with water to form *carbonic acid* (H2CO3)

which will then dissociate to form *hydrogen carbonate* ions and hydrogen ions (HCO3– + H+)

these will be absorbed by autotrophs to form organic compounds

is all carbon dioxide dissolved in water into carbonate acid

no, some will remain as dissolved gas

what happens When the hydrogen carbonate ions come into contact with the rocks and sediments on the ocean floor

they acquire metal ions, resulting commonly in the formation of calcium carbonate and the development of limestine

2 ways calcium carbonate is formed

 -when hydrogen carbonate ions come into contact with the rocks and sediments on the ocean floor

\-living animals can combine the hydrogen carbonate ions with calcium to form calcium carbonate eg. top form shells

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what happens when coral dies

the hardcomponents can become fossilised in limestone

formation of calcium carbonate overview

methanogens

prokaryotes that produce methane as a biproduct in anaerobic conditions

where are mathanogens found

* Wetlands (e.g. swamps and marshes)
* Marine sediments (e.g. in the mud of lake beds)
* Digestive tract of ruminant animals (e.g. cows, sheep, goats)

2 key biproducts on anaerobic digestion that methanogens produce methane from

acetic acid and co2

acetic acid=

Methane and Carbon Dioxide  (CH3COO– + H+  →  CH4 + CO2)

carbon dioxide + hydrogen-=

Methane and Water  (CO2 + 4 H2  →  CH4 + 2 H2O)

stages of methane production in a ruminant

hydrolysis (polymers to monomers)

acidogenesis (monomers to alcohols)

acetogenesis (alcohols to acetate)

methanogenesis (acetate to methane)

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methanogenic archaeans

break down peat in anaerobic conditions to produce methane

what happens to methane in the atmosphere

naturally oxidised to form co2 and water(why methane levels in the atmosphere are not very large, even though significant quantities are being produced  )

what type of bacteria and fungi will decompose dead organism+return nutrients to the soil

saprotrophic bacteria and fungi, the decomposition requires o2

how are fossils formed

partial decomposition

example of where partial decomposition occurs

water logged areas

why does partial decomposition occur in water logged areas

 may lack oxygenated air spaces within the soil and thus possess __anaerobic conditions__

anaerobic respiration produces organic acids resulting in acidic conditions which saprotrophic b+f cannot function effectively preventing decomposition

how is coal formed

due to r partial decomposition, carbon-rich molecules remain in the soil and form **peat. When compressed under sedim ent heat and high pressure force out impuritys and moisture. t**he remaining material has a high carbon concentration and undergoes a chemical transformation to produce **coal**

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how is oil/natural gas formed

marine organisms decay on ocean floor

* Sediments (e.g. clay and mud) are deposited on top of the organic matter, creating anoxic conditions that prevent decomposition (partial decomposition)
* As a result of the burial and compaction, the organic material becomes heated and hydrocarbons are formed
* The hydrocarbons form **oil** and **gas**, which are forced out of the source rock and accumulate in porous rocks (e.g. sandstone)

anoxic condition

A condition in which the aquatic (water) environment does not contain dissolved oxygen (DO), causing partial decomposition

why arent fossil fuels renenwable

formation takes place over millions of years

combustion

occurs when hydrocarbons are heated in the presence of oxygen. complete produces water, co2 and energy(exergonic reaction), in complete= carbon monoxide instead of dioxide

2 combustion sources

fossil fuels and biomass(eg. bioethanol/biodiesal)

why is biomass con sidered a renewable energy source

* Living organisms produce hydrocarbons as part of their total biomass (either for use or as a waste product)
* These hydrocarbons can be extracted and purified to produce an alternative fuel source (e.g. bioethanol and biodiesel)
* Provided new raw materials are provided and waste products are removed, this source of energy is renewable

carbon fluxes

describe the rate of exchange of carbon between the various carbon sinks / reservoirs(lithosphere, hydrosphere,atmosphere, biosphere)

measured in gigatons

what effects the rate of exchange in carbon fluxes

* *Photosynthesis* – removes carbon dioxide from the atmosphere and fixes it in producers as organic compounds 
* *Respiration* – releases carbon dioxide into the atmosphere when organic compounds are digested in living organisms
* *Decomposition* – releases carbon products into the air or sediment when organic matter is recycled after death of an organism
* *Gaseous dissolution* – the exchange of carbon gases between the ocean and atmosphere
* *Lithification* – the compaction of carbon-containing sediments into fossils and rocks within the Earth’s crust (e.g. limestone)
* *Combustion* – releases carbon gases when organic hydrocarbons (coal, oil and gas) are burned as a fuel source

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the size of carbon fluxes/sinks are

estimated

3 main cuases for flux change

climate conditions, natural events and human activity 

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how does climate change affect carbon fluxes

• Rates of photosynthesis will likely by higher in summer seasons, as there is more direct sunlight and longer days

• Oceanic temperatures also determine how much carbon is stored (lower stored in higher temps) as dissolved CO2 or as hydrogen bicarbonate ions

• Climate events like El Nino and La Nina will change the rate of carbon flux between ocean and atmosphere

• Melting of polar ice caps will result in the decomposition of frozen detritus

how do natural events affect carbon fluxes

* Forest fires can release high levels of carbon dioxide when plants burn (loss of trees also reduces photosynthetic carbon uptake)
* Volcanic eruptions can release carbon compounds from the Earth’s crust into the atmosphere

how does human activity affect carbon fluxes

* Clearing of trees for agricultural purposes (deforestation) will reduce the removal of atmospheric CO2 via photosynthesis
* Increased numbers of ruminant livestock (e.g. cows) will produce higher levels of methane
* The burning of fossil fuels will release carbon dioxide into the atmosphere

continuos and regular carbon flux patterns

* CO2 levels fluctuate annually (lower in the summer months when long days and more light increase photosynthetic rates)
* Global CO2 trends will conform to northern hemisphere patterns as it contains more of the planet’s land mass (i.e. more trees)
* CO2 levels are steadily increasing year on year since the industrial revolution (due to increased burn

explain hopw increased levels of atmospheric co2 contribute to global warming

1. short wave/UV radiation from the sun passes through the atmosphere/reaches the Earth’s surface;

2. which warms the (surface of the) Earth;

3. long wavelength/infra-red radiated from the (warmed) Earth’s surface;

4. carbon dioxide absorbs/traps long wavelength/infra-red radiation;

5. more heat trapped in/less heat escapes from atmosphere with more carbon dioxide;