The carbon cycle - stores and transfers

what is the carbon cycle

transfer of carbon from organic (matter derived from living things) carbon to inorganic carbon (compounds derived from non-living things) and back again.

what is a carbon sink

store absorbs more carbon than it releases e.g. rainforest

carbon source

store that releases more carbon than it absorbs e.g. rainforest being burnt

what are the 5 major carbon stores

Lithosphere, hydrosphere, biosphere, atmosphere, cryosphere

what is the lithosphere

crust and upper mantle

what carbon is stored in the lithosphere

organic e.g. leaf litter and inorganic e.g. fossil fuels like coal

4 stores of carbon in the lithosphere

marine sediment (100 million GtC) - largest

soil organic matter

fossil fuel despositss

peat (dead, undecayed organic matter)

amount of oceanic carbon in hydrosphere

37,000 - 40,000 GtC

3 subdivisions of the oceanic stores (hydrosphere)

surface layer (euphotic zone) - sunlight can penetrate allowing photosynthesis to occur

intermediate and deep later - twilight zone - largest store

living organic matter like fish and dissolved organic matter

what happens when an organism dies in the ocean

sinks to deep water, decays, releases CO2 into deep water, some material sinks to bottom where it forms layers of carbon-rich sediment.

what happens to the carbon rich sediment over millions of years

chemical and physical processes turn it into rocks which can store carbon for millions of years

what is the biosphere

total sum of all living matter

2 types of biosphere

terrestrial (land) and oceanic

estimated carbon stored in terrestrial biosphere

3000 GtC

what does the distribution of carbon in the terrestrial biosphere depend on

type of ecosystem e.g. highest is tropical rainforests at 25%, lowest is deserts at 5%

5 stores of the terrestrial biosphere

living vegetation - mostly plant tissue - 19%

plant litter - undecomposed plant debris, 70% plant litter is wood - wood litter increases as the forest ages. less carbon stored in grassland as there’s less plant tissue

animals - store and transfer carbon

peat - accumulation of partially decayed organic matter

soil hummus

what does the amount of carbon stored in living vegetation depend on

vegetation type e.g. 50% of the carbon stored in forests is in high altitude forests and less than 33% in low altitude

what is one of the largest forest reservoirs

of the total carbon stored in the terrestrial vegetation the amazon holds around 20%

how is peat formed

almost permanent water saturation in the ground obstructs oxygen flow from atmosphere to ground creating low oxygen anaerobic conditions leading to slow rates of decomposition

how much carbon is estimated to be stored in peat

250 GtC

what is soil hummus

thick brown substance left after most organic litter has decomposed. spread throughout the soil by organisms like worms

how many times bigger is the soil storage than atmospheric storage

3.1x

is the oceanic store bigger or smaller than the soil store

bigger

in tropical rainforests how much carbon is stored in soil

50%

types of carbon stored in soil

organic and inorganic

have atmospheric carbon levels changed

fluctuates over earth’s history - peaked in Cambrian period (7000ppm), lowest in last 2 million years (quaternary glaciation - 180ppm)

level of CO2 in atmosphere today

only a trace gas - low concentration necessary for life.

where is atmospheric carbon measured

Hawaii - remote location so air undisturbed with minimal influences from vegetation or human activity

atmospheric carbon change from industrial revolution

1953 - 280ppm

2015 - 400ppm

how can past atmospheric carbon be measured

ice cores

what is the cryosphere

frozen ground like permafrost in tundra regions

amount of carbon stored in cyrosphere

1700GtC

what are the 8 processes driving change in the magnitude of carbon stores (movement of carbon and carbon transfers) and their speed

Weathering, combustion, burial and compaction - slow, photosynthesis -fast, decomposition -fast, respiration -fast, oceanic carbon pumps - slow, carbon sequestration

outline weathering

atmospheric carbon dissolved in water forming carbonic acid. Carbon acid reacts with minerals on earth’s surface dissolving them into their component ions through chemical weathering process - component ions then carried in surface water e.g. rivers to the ocean where they settle as minerals -often forms of calcium carbonate.

Outline burial and compaction

marine organisms containing calcium due and collect at ocean floor as sediment which is then buried by more sediment turning the original sediment into sedimentary limestone. Biosphere to lithosphere then potentially to atmosphere.

what can tectonic plates do to the sedimentary rock

tectonic uplift exposes buried limestone e.g. Himalayas where some peaks formed by material once at the bottom on the ocean

tectonic plate movement can push sea floor under continental margins so the carbon sea deposits melt and rise back to the surface through volcanic eruptions meaning the CO2 returns to the atmosphere

outline photosynthesis

phytoplankton in euphotic zone, terrestrial plants etc turn carbon into organic matter. use energy from sunlight to combine carbon dioxide with water to form carbohydrates which store energy. oxygen released into atmosphere as by-product. Transfer from atmosphere to biosphere.

outline respiration

oxygen from atmosphere combined with carbohydrates (glucose). water and carbon dioxide as by-product. transfer from biosphere to atmosphere. organisms use stored carbohydrates as energy to carry out functions like respiration. some carbohydrates remain as biomass - consumers e.g. animals get their energy from this excess biomass.

what is decomposition

physical, chemical and biological mechanisms that convert organic matter into an increasingly stable form. Transfer from biosphere to atmosphere, lithosphere and pedosphere

what carries out decomposition

decomposer e.g. bacteria of fungi - break down the cells of dead organism into large biomolecules then into atoms

purpose of decomposition

ensures important elements e.g. carbon are recycled to enable further plant growth

what is leaching

physical process where elements from decomposition are transferred from the soil to the water system

one chemical process of decomposition

oxidation

one biological transformation of deposition

digestion aided by catalytic enzymes

outline the process of vertical deep mixing

negative correlation between water temp and amount of dissolved CO2 leads to vertical deep mixing.

when does vertical deep mixing occur

when warm oceanic surface currents are carried from the warm tropics to the colder polar regions. water is cooled (absorbs more CO2) so becomes more dense and sinks. when cold water returns to the surface it heats up, losing its CO2 into the atmosphere.

what does vertical deep mixing ensure

ensures CO2 constantly exchanged between ocean and atmosphere and helps ocean absorb as much CO2 as possible as the surface water is constantly replenished (carbon pump).

what is the carbon transfer with vertical deep mixing

atmosphere to hydrosphere

what are Biological carbon pumps

living organisms in ocean move carbon from atmosphere into surface water, then into deeper water and rocks. organisms containing carbon die and sink into deep water where it forms layers of carbon-rich sediment. Chemical and physical processes can turn this into rock which locks up carbon.

what is the carbon transfer for biological carbon pumps

Transfer from atmosphere to biosphere then lithosphere

when does combustion occur

when any organic matter is reacted with the presence of oxygen to form carbon dioxide, water and energy.

what is biomass combustion

burning of living or dead vegetation - includes wildfires and human-induced burning

what happens after a severe fire

new tree growth can occur - if forest fully replaces itself there will be no net carbon change over that life cycle

how much carbon is emitted into the atmosphere by fires

20%

where are fires common

Boreal forests of China, savannah grassland in South Africa and tropical rainforests in Brazil

what determines whether a forest is a net carbon source or sink

number of trees absorbing carbon through photosynthesis, number of old trees decomposing and releasing carbon and the amount of carbon stored in the organic soil layer

what enabling increasingly large fires to occur

global warming and changing precipitation levels which can change the carbon balance

what is carbon sequestration

capturing CO2 from atmosphere and putting it into long term storage. Movement of carbon between atmosphere, hydrosphere and lithosphere.

what is geological sequestration

CO2 captured at source e.g. powerplant and injected in liquid form into stores underground e.g. depleted oil reservoirs or the deep ocean - still at experimental stage

what is carbon put into the deep ocean

capable of absorbing more additional carbon than terrestrial systems because of its size

one advantage of carbon sequestration

carbon will sink within weeks of it being captured

what is terrestrial or biological sequestration

use of plants to capture CO2 from atmosphere where its stored in plant tissues.

what is the aim of biological or terrestrial sequestration

develop set of land management strategies which maximise the amount of carbon that remains in the soil and plant material for a long time

benefit of biological or terrestrial sequestration

enrich wildlife

3 disadvantage of biological or terrestrial sequestration

forests used to capture carbon may lose the carbon back to the atmosphere in forest fires

land based sequestration plantations are slow growing and require active monitoring for the lifetime of the plantation

the carbon removed from the atmosphere isn't permanently stored.

 

what is a sere

a succession that relates to a specific environment. each stage of a sere is called a seral stage.

example of a sere

lithosere - a vegetation succession that occurs on bare rock

what is the terrestrial carbon cycle: the lithosere (vegetation succession)

rock exposed for first time e.g. after glacial melt - vulnerable to weathering which releases carbon

vegetation grows on exposed rock - carbon exchange (respiration and photosynthesis)

organic matter added to broken rock fragments - soil develops

soil can store and absorb carbon

plant species become more diverse

different habitats established

what is the final stage in the lithosere

usually occurs as a result of the climate (climatic climax) - the climax vegetation for a lithosere in the UK is normally deciduous woodland

outline the carbon cycle at plant level

CO2 enter tree via photosynthesis, carbon atoms move to soil, leaf litter, roots, stem and the atmosphere. over time tree takes in more carbon by photosynthesis and releases some via respiration so it grows and increases in biomass. carbon atoms can be stores in new organic carbon compounds created by biosynthesis so more carbon is stored.