Studied by 9 people
What is the carbon cycle?
what sort of system is it?
what is it made up of?
what would be equal for the carbon cycle to be in equilibrium?
What will changes in the system result in?
It is the biochemical cycle by which carbon moves from one sphere to another.
It is a closed system.
It is made up of inputs, through-flows and outputs.
The carbon cycle would be in equilibrium if the carbon sinks equate to the carbon sources.
Changes in the system may result in positive (exaggerating) or negative (reducing) feedback.
What are the different spheres which carbon exists in?
Atmosphere- as carbon dioxide and carbon compounds e.g. methane
Hydrosphere- dissolved CO2
Lithosphere- as carbonate in limestones, chalk and fossil fuels, as pure carbon in graphite and diamond
Biosphere- as carbon atoms in living and dead organisms
(also the Cryosphere- contains the frozen parts of the planet)
What are the different fluxes between the spheres and how many pentagrams of carbon are transferred by them annually? + what are the three main/largest ones ?
Photosynthesis (transfers carbon from the atmosphere to the biosphere and the hydrosphere) 123 PgC/yr
Respiration and fire (biosphere and hydrosphere to atmosphere) 118.7 PgC/yr.
Soil to River (bio to hydro) 1.7 PgC/yr
Rock weathering (litho to either hydro or atmo) 0.4 PgC/yr
Burial 0.2 PgC/yr
Freshwater Outgassing 1.0 PgC/yr
Volcanic Eruptions 0.1 PgC/yr
Fossil fuel use and cement production 7.8 pgC/yr
Ocean to atmosphere 78.4 PgC/yr
Atmosphere to Ocean 80 PgC/yr
River to sea 0.9 PgC/yr
Land use change 1.1 PgC/ yr
What is reservoir turnover?
the rate at which carbon enters and leaves a store
How can humans alter the spheres/fluxes of carbon? (Anthropogenic)
burning fossil fuels
heating rock containing calcium carbonate for increased cement manufacturing
carbon capture and storage - filtered with a pipe at a power station leading to empty geological formations
Afforestation
farming rice (bacteria decomposes organic matter)
farming cattle
deforestation
What is the slow carbon cycle?
the long term storage of carbon
marine organisms build their shells by combining calcium with carbon
they die and accumulate on the ocean floor, over millions of years they become compressed into carbon-rich sedimentary rock
usually stored for 150 mil years
oceanic crust - containing the rock is subjected and this causes the crust to melt
co2 is released into atmosphere through volcanic eruptions and chemical weathering
FF store carbon for mils of years
What is the fast carbon cycle?
ten to one thousand times faster than the slow cycle
involves transfer of C between biosphere, atmosphere and hydrosphere
co2 is absorbed by phytoplankton by photosynthesis - then stored in their tissues as carbohydrates
respiration releases co2 to the atmo
co2 is exchanged between atmo and hydro with it being dissolved in the surface water and returning by evaporation
then returned to earth- soil and vegetation as acid rain
What are the different processes/pathways of the carbon cycle?
Precipitation
acid rain is weak carbonic acid
flows back to land and oceans
CO2 concentration in the air is increased due to human actions which increases rain acidity which therefore increases ocean acidity which causes coral bleaching
Combustion
When organic material burns
co2 is released
occurs naturally by wildfires
leads to increased nutrient and carbon recycling and results in growth being stimulated> essential for East African grassland ecosystems
human activities increase this (burning FF and biomass fuels)
Photosynthesis
converting light energy into chemical energy that can be later transformed for the organism’s activities
chemical energy is stored in carbohydrate molecules such as sugars which are manufactured from CO2 and water
Glucose is used as the building blocks of cellulose, for respiration to provide energy and to be converted into lipids.
Respiration
reverse of photosynthesis
releases energy by breaking sugars
CO2 is released into the atmo
Decomposition
carbon is released as CO2 when living organisms die and are decomposed.
the temp. has a significant impact on the rate of decomposition
it’s fast in tropical rainforests
slow in the arctic tundra
Burial and Compaction
organic matter is buried by sediment and becomes compacted
over millions of years this organic sediment containing carbon may form hydrocarbons such as coal and oil. Shelled organisms absorb co2 from the water and convert it to calcium carbonate
when they die they dissolve and release co2
the rest of them gets compacted, forming limestone which stores carbon for millions of years
Carbon Sequestration
the transfer of carbon from the atmosphere to plants, soil, oceans and rock formations
occurs both naturally and by humans (carbon capture)
Weathering
the breakdown of rocks in situ close to or on the surface of the earth either physically, biologically or chemically
chemical - acid rain
limestone - calcium carbonate +solution > calcium bicarbonate which is soluble so dissolves
0.3 billion tonnes of C are transferred from rocks to the atmosphere and oceans every year.
What are the different stores of carbon and how many Pentagrams of Carbon do they store?
+ what are the 3 largest?
what can impact them?
Permafrost store: 1,700 PgC
Fossil fuel organic carbon store: 1,471 PgC
soil store: 1,950 PgC
terrestrial ecosystem store: 550 PgC
Atmosphere store: 589 PgC
Marine biota store: 3 PgC
Dissolved organic carbon store: 700 PgC
Sedimentary rock store 83,000,000 PgC
ocean floor calcareous ooze store: 1,750 PgC
Surface Ocean Store: 900 PgC
Intermediate and deep ocean store: 37,100 PgC
these are impacted by human activity
How do sedimentary stores form?
1. Shelled organisms and coral absorb CO2 from the water and convert it into calcium carbonate which builds their shells.
2. When these organisms die they accumulate on the sea bed. (fall as marine snow)
3. Sediment is deposited in layers in a low-energy environment e.g. lake or sea bed. This is made up of crustaceans, coral and plankton.
4. Further layers are deposited and sediment undergoes diagenesis (the physical and chemical changes that occur during the conversion of sediment to sedimentary rock).
5. The lower layers become compressed and chemical reactions cement particles together converting loose, unconsolidated/unsorted sediment into solid rock is known as lithification.
6. Carbon dioxide is released as the carbonates dissolve. The remainder becomes compacted, forming limestone which stores carbon for millions of years.
7. 80% of lithospheric carbon is found in limestones. Limestone is formed when shelled marine organisms die. Their shell fragments fall to the ocean floor and become compacted over time.
8. Over millions of years, this organic sediment containing carbon may form hydrocarbons such as coal and oil through heat and pressure (metamorphosis)
How do sedimentary stores release carbon?
1. Water reacts with carbon dioxide in the atmosphere à carbonic acid which falls to the ground in rainwater
2. Rivers transport calcium ions from the land to the oceans which combine with bicarbonate ions to form calcium carbonate
3. Deposition and burial turns the calcite sediment into limestone
4. There is over 100million PgC in the lithosphere.
5. Subduction at destructive margins and tectonic uplift can expose the buried limestone.
6. The carbon-rich sedimentary rocks are in contact with extreme heat à chemical changes
7. CO₂ is returned to the atmosphere
8. The gas released by volcanic eruptions is relatively insignificant in comparison to human activity
- Volcanoes currently emit 0.15 - 0.26 Gt carbon dioxide annually
- Fossil Fuel use emits about 35 Gt
9. Outgassing happens at:
- Volcanic zones associated with plate boundaries (including subduction zones and spreading ridges)
- Areas with no current volcanic activity, e.g., the geysers in Yellowstone National Park, USA
- Direct emissions from fractures in the Earth’s crust
Why do CO2 levels fluctuate?
What has been happening to global CO2 levels over the last 700 million years?
What is responsible for the current low levels of co2?
vegetation comes and goes
volcanoes can go extinct or erupt
continents drift over the face of the earth
interglacial vs glacial periods
winter vs summer
day vs night
human activity - population growth, covid lockdowns
levels have been decreasing
mountain-building e.g. Himalayas, Andes, Rockies
what is the net primary productivity?
Amount of CO2 vegetation takes in through photosynthesis - amount vegetation release during respiration
How does Air-sea surface exchange work?
c02 diffuses into the oceanic carbon cycle
molecules of it enter the ocean by diffusing into sea surface waters and dissolving
the amount depends on variables such as - wind, sea surfacing mixing, concentrations of co2 and the temperature of the water
what is the oceanic biological carbon pump?
what 3 things does it play a major role in?
Organic sequestration of Carbon from the atmosphere and surface runoff to ocean interior + sea floor sediments
The sum of processes of photosynthesis, respiration, excretion, decomposition
it plays a major role in
-transforming carbon compounds into new forms of carbon compounds
-moving carbon throughout the ocean
-moving carbon down to seafloor sediments
it transfers 11 gigatonnes of carbon every year into the oceans interior
What is marine snow?
a shower of organic material falling from upper waters to the deep ocean
biological debris ( animals and plants near the surface die and decay and fall, also includes sand, soot, inorganic dust and faecal matter)
continuous snowstorm provides food for many deep sea creatures (like giant marine isopods!) there is a lot of carbon and nitrogen in marine snow
the small percentage of material not consumed in shallower waters becomes incorporated into the muddy calcareous ooze blanketing the ocean floor, where it is further decomposed through biological activity.
about ¾ of the deep ocean floor is covered in this thick, smooth ooze. The ooze collects as much as 6m every million years.
only 0.1% of the carbon drawn into the ocean makes it to the very depths where it can no longer be exchanged with the atmosphere.
What role do phytoplankton play in the oceanic carbon cycle?
Phytoplankton are single-celled organisms that drift in the sunlit surface areas of oceans forming plumes. They can photosynthesise and respire.
They are the key to sequestering carbon down into the oceanic biological pump from the atmosphere.
the shallower depths are more biodiverse which leads to rapid carbon recycling as animals feed on each other and respiration returns carbon.
Phytoplankton are eaten by zooplankton and in turn higher tier consumers, each time through feeding, excretion, dying and decomposition carbon is moved through the ocean.
What is the physical carbon pump/ ocean conveyor?
currents circulate water through oceans like a giant conveyor belt, carrying heat from the tropics towards the poles and sending colder water back into deep ocean currents
wind, temp and salinity help drive them.
AMOC
the Atlantic meridian overturning circulation- sometimes referred to as the ‘conveyor belt of the ocean’ acts as a major heat-transporting system, bringing war water from the tropics to the north Atlantic and cold water back to the southern hemisphere towards Antarctica
The AMOC is the main reason why the northern hemisphere is warmer than the southern hemisphere. The massive movement and release of heat makes the northern Atlantic and surrounding land areas – like much of Europe – several degrees warmer than they would be otherwise.
what is meant by thermohaline circulation?
the ocean consists of almost entirely of water and salt. The density of ocean water depends on both temperature (T) and salinity (S). The thermohaline circulation of the ocean refers to the flow of ocean water caused by changes in density.
Evaluate the importance of oceans as a carbon sink
- Definitions: A carbon sink is an area that absorbs more carbon through photosynthesis/diffusion than it releases, they are vital to protect against extreme temperatures increasing and increases in carbon emissions.
- The different oceans across Earth act as carbon sinks because the organisms (phytoplankton and algae) inside of them photosynthesise and therefore take in carbon dioxide from the atmosphere to the hydrosphere and eventually into the slow carbon cycle once that carbon becomes sedimentary rock (e.g. limestone) on the sea floor.
Importance of oceans as a carbon sink:
- Oceans take in 25% of all CO2 emissions and capture 90% of the heat that is generated by these emissions.
- They are a vital buffer against the impacts of climate change.
- Coral reefs take in CO2 through the algae (which they share a symbiotic relationship with) photosynthesising.
- Forests are also a significant store, as is permafrost (1,700PgC) and soil/peat bogs
On the other hand- they are less important because...
- Due to climate change increasing Earth’s temperatures the ocean is getting damaged- e.g., coral bleaching and ocean acidification is occurring, and the oceanic carbon sink is not able to take in as much carbon as is necessary.
Conclusion/ Judgement:
- Overall, the oceans play an important role in both the fast and slow carbon cycle and they take in so much carbon that as a sink they are very significant.
Outline how oceans recycle carbon at a variety of timescales
As the food chain undergoes phytoplankton is eaten by zooplankton and this eventually leads to larger marine animals like whales storing carbon for a long period of time. This takes long periods of time to release due to these animals having long lifespans and decomposing after death. Limestone also stores carbon for billions of years until it is broken by mining or quarrying.
Describe the process of thermohaline circulation
Down welling currents occur in areas where cold, denser water sinks. (e.g. the poles) These down welling currents bring dissolved CO2 down to the deep ocean. Once there, the CO2 moves into slow-moving deep ocean currents staying there for hundreds of years, slowly redistributing the dissolved carbon. Some will also be incorporated into 'marine snow'
Eventually, these deep ocean currents return to the surface in a process called upwelling. Many upwelling currents occur along coastlines. When upwelling currents bring deep, cold ocean water to the surface, the water warms and some of the dissolved CO2 is released back to the atmosphere. Down welling and upwelling currents are important components of the deep ocean conveyor belt and are important in physically transporting carbon compounds to different parts of the oceans.
Warm water - upwelling of less dense water - CO2 less soluble so harder to store - diffuses into the atmosphere.
how does ice melting affect the Thermohaline circulation?
more freshwater means lower salinity so more less dense water so upwelling will occur instead of downwelling.
explain how terrestrial primary producers sequester carbon during photosynthesis
tropical rainforests collectively sequester more carbon from the atmosphere than temperate or boreal forest, but they are also increasingly destroyed for agricultural expansion.
Of the 3 largest rainforests only the Congo has enough left standing to have remained a strong net Carbon sink
- Congo's Tropical rainforest sequesters 600million metric tonnes more CO2 than it emits
What is the positive feedback loop from increased co2 in the atmosphere (on oceans)
the solubility of CO2 in water decreases as the temperature of the water increases
this is important for the climate system because as the oceans warm, CO2 is released into the atmosphere as it can no longer be stored in the oceans.
this is known as a positive feedback mechanism (exacerbates the problem as a small change leads to a bigger change)
the release of CO2 into the atmosphere could lead to increased trapping of heat from the sun and most scientists believe increases in greenhouse gases in the atmosphere are causing global warming.
what are the different residence times for different stores?
geological stores- 150 mil years
terrestrial stores- 18 years
seafloor sediments - 2500 years
oceans- 25 years
soil storage of carbon
-what percent of carbon emissions do they sequester
Soil stores are 20-30% of global carbon sequestering - twice the quantity of carbon in the atmosphere and three times the carbon of vegetation.
However soils can store or emit carbon depending on local conditions.
What process puts carbon particles into the soil from rocks and minerals?
What other component of soil speeds up this process?
Where does the soil organic matter come from?
As with the oceans, at what depth in the soil do you think carbon cycling and formation is most active?
Weathering
Moisture
Decomposing plants and animals
organic layer
What is soil composed of?
air 25%
water 25%
mineral particles 45%
organic matter 5%
organisms 10%
roots 10%
humus 80%
outline the soil profile
- O horizon- high % organic matter, humus
- A horizon - rich in organic matter
- B horizon - subsoil - litter humus, soluble minerals- also called zone of accumulation.
- C horizon - weathered bedrock
features of healthy soils include:
are dark, crumbly and porous
contain many worms and microorganisms
provide air, water and nutrients for micro-organisms and plants to thrive.
contain more carbon or organic matter
sequester carbon
usually improve resilience to wetter weather because they enable infiltration and percolation of water (reducing soil erosion and flood risk)
retain moisture which regulates soil temperature during heatwaves ad reduces the effects of droughts
why do biomes of temperate regions such as those of Northern Europe create healthier soils which trap more carbon than arid desert soils
biomes of temperate regions trap more carbon because of healthier soils, these soils are characterised by the amount of micro-organisms that live in them (which are the organic matter that acts as a medium for transport and storage of carbon), their ability to retain moisture and contain water and nutrients. Areas in Northern Europe such as peatlands are formed in waterlogged conditions that slow down plant decomposition, this allows for the buildup of organic matter. Boreal forests also have healthy soils as they are stable ecosystems where the animals contribute to the nutrient cycle and the soils can trap carbon through microorganisms getting buried.
On the other hand, arid desert soils are located in harsh, hot climates where the ecosystem is much more delicate as less species are perfectly adapted to live there. Therefore the soil is very lacking in nutrients as whatever animals that die are quickly taken by desperate predators. The dry desert atmosphere means that less moisture is retained so it is not easy for the soils to take in CO2.
What is permafrost?
permanently frozen ground composed of rock, soil, sediments and varying amounts of ice that bind the elements together - it remains frozen for 2 or more consecutive years.
It can be from 3 feet to 4,900 feet thick. It stores the carbon based remains of plants and animals that froze before they could decompose.
How is it that permafrost is such a large carbon trap?
these regions are too cold for microbes to decompose organic matter so it remains trapped in the soil.
why can the melting of these soils create a positive feedback loop in the carbon cycle?
as co2 is released
