Topic 6 - EQ1 - Carbon

Question 1

What is the arguably most important role of carbon on earth?

Answer 1

The role a balanced carbon cycle has in regulating the climate of earth making it warm enough to survive.

Question 2

Is carbon a common element in the composition of the planet earth?

Answer 2

Yes, carbon is a common element. It exists in gas, liquid and solid forms, in biotic/organic and abiotic/inorganic forms. Carbon moves between these forms (carbon pathway) through natural (biogeochemical) processes over a range of spatial and time scales.

Question 3

What is carbon sequestering?

Answer 3

The natural storage of carbon by physical or biological processes, such as photosynthesis or degradation.

Question 4

Is the carbon cycle an open or closed system?

Answer 4

It is a closed system. It does not have any external inputs or outputs, therefore, the total amount of carbon is constant and finite.

Question 5

What are stores within the carbon system?

Answer 5

Where carbon is held (whether that be in reservoirs, pools or stocks)

Question 6

What are fluxes within the carbon system?

Answer 6

The movement or transfer of carbon between stores

Question 7

What are processes within the carbon system?

Answer 7

The physical mechanism which drive the fluxes between stores.

Question 8

What are the four main carbon stores?

Answer 8

-The atmosphere gases (e.g. carbon dioxide, methane…)
-The hydrosphere - dissolved CO2 in oceans, lakes…
-The lithosphere - carbonates in limestone and fossil fuels
-The biosphere - living and dead organisms

Question 9

What is the largest carbon store?

Answer 9

Sedimentary rock store in the lithosphere (83 million PgC)

Question 10

What is the largest flux of carbon?

Answer 10

Photosynthesis (123PgC/year)

Question 11

Which is larger the terrestrial, oceanic or atmospheric carbon store?

Answer 11

Terrestrial then oceanic then atmospheric

Question 12

What is the slow (long term) carbon cycle?

Answer 12

The geological carbon cycle

Question 13

What is the fast (short term) carbon cycle?

Answer 13

The biogeochemical carbon cycle

Question 14

What is the geological carbon cycle?

Answer 14

A natural cycle that moves carbon between land, oceans and the atmosphere. Within the cycle there tends to be a natural balance between carbon production and absorption within this cycle, but there can be occasional disruptions and short periods before the equilibrium is restored, such as when major volcanic eruptions emit large quantities of carbon dioxide into the atmosphere, or when natural climate changes occur.

Question 15

What are the six stages of the geological carbon cycle?

Answer 15

1 - Carbon held within the mantle is released into the atmosphere as CO2 when volcanoes erupt (it is known as ‘out-gassing’)
2 - CO2 within the atmosphere combines with rainfall to produce a weak acid rain (carbonic acid rain) that weathers and dissolves carbon rich rocks releasing bicarbonates
3 - Rivers transport weathered carbon and calcium sediments to the oceans (lots of CO2 there) where they are deposited
4 - Carbon in organic matter from plants and animal shells/skeletons sink into the ocean bed when they die leading to build up of carbon on sea floor alongside a coal strata at the margins of land and sea
5 - Carbon rich rocks are subjected along plate boundaries and eventually emerge again when volcanoes erupt
6 - The presence of intense heating along subduction plate boundaries metamorphoses sedimentary rocks rich in carbonates by baking, makes them magma and releases carbon dioxide

Question 16

What are four examples fluxes within the carbon cycle?

Answer 16

-Photosynthesis
-Respiration
-Outgassing from volcanic eruptions
-Sedimentation

Question 17

How does the biogeochemical carbon cycle roughly work?

Answer 17

-Combustion of biomass and fossil fuels releases CO2 and other greenhouse gases into the atmosphere
-Photosynthesis in plants removes CO2 from the atmosphere
-Respiration releasing CO2 into the atmosphere as animals consume plants and breathe
-The decomposition of dead plants and animals releases CO2 into soils and deposits carbon on the sea floor
-Biofuels and carbon on the sea floor become fossil fuels over thousands of years, they are then combusted and the cycle restarts

This cycle has become much more important since the Industrial Revolution.

Question 18

How does the carbon cycle maintain an equilibrium?

Answer 18

Via negative feedback cycles.

E.g. after volcanic eruptions extra CO2 is emitted into the atmosphere. This CO2 results in higher temperatures and more atmospheric moisture (as a result of greater evaporation). The result is acid rain which falls and weathers rocks and creates bicarbonates which eventually make their way onto the sea floor which slowly removes carbon from the atmosphere and brings it back to the lithosphere, in turn rebalancing the carbon cycle.

Question 19

Why are there concerns over carbon emissions from human activity if there are natural processes to maintain equilibrium?

Answer 19

Because of the rate of carbon emissions from humans. The atmosphere is filling up with CO2 much quicker than plants and oceans can absorb it.

Question 20

Why do carbon fluxes vary with latitude?

Answer 20

More to do with the type of vegetation which varies by latitude. In the evergreen forests/rainforests of the equator, carbon sequestration happens year round, however, in mid latitudes with deciduous woodlands, the trees have months of dormancy where they lose their leaves (no photosynthesis) and so carbon sequestration is not year round. + soil carbon sequestration slower in high latitudes as it is colder so decomposition takes longer

Question 21

Why are carbon dioxide levels higher in the northern hemisphere?

Answer 21

The majority of people live in the Northern Hemisphere, and it is where the majority of industrial activity takes place.

Question 22

Through what process do limestone rocks store carbon? (part of how geological processes store carbon for a long period of time)

Answer 22

Limestone rocks contain a high concentration of calcium carbonate.

Limestone is formed partly from shell building organisms, such as corals, which are carbon rich as a result of extracting carbon from seawater, and partly from marine phytoplankton which absorb carbon through photosynthesis. Their carbon rich remains accumulate on the ocean floor where over a long period of time they are cemented together and lithified by the weight of water into limestone.

Question 23

Through what process does shale store carbon? (part of how geological processes store carbon for a long period of time)

Answer 23

Biologically derived carbon in rocks, like shale, is formed when carbon from organisms is embedded in layers of mud. Over millions of years, heat and pressure compress the mud and carbon, forming shale.

Question 24

Through what process do fossil fuels store carbon? (part of how geological processes store carbon for a long period of time)

Answer 24

Fossil fuels, such as coal, were made up to 300 million years ago from the remains of dead organic material. Organisms once dead, sank to the bottom of rivers and seas, were covered in silt and mud, and then started to decay anaerobically (without oxygen). This process operates over millennia. When organic material builds up faster than it can decay, layers of organic carbon become fossil fuels instead of shale.

Question 25

What are the geological processes that influence levels of carbon in the atmosphere?

Answer 25

The chemical weathering of rocks + volcanic outgassing

Question 26

How does the chemical weathering of rocks affect the level of carbon in the atmosphere?

Answer 26

Chemical weathering of rocks happens when CO2 in the atmosphere combines with precipitation to form a weak carbonic acid rain.
-When the rain falls it reacts with rocks to form carbonates, these carbonates are carries by rivers to the oceans (alongside some subaerial processes at the coastline).
-Marine organisms in the oceans sequester carbon in shell building which eventually form sedimentary carbonate rocks.
-Tectonic spreading brings carbon rich sedimentary rock into contact with extreme heat, which causes chemical changes and the release of CO2 back into the atmosphere.

Question 27

How does volcanic outgassing affect the level of carbon in the atmosphere?

Answer 27

Volcanic outgassing is when carbon is emitted into both the atmosphere and the ocean through a process known as out-gassing.
-CO2 contained in mantle fluids is vented from terrestrial stores of carbon
-At points of shallow crustal depth in subduction zones (e.g. Mt Pinatubo in the Philippines), subducted carbon sources such as coal or oil shales are oxidised into CO2 and vented back into the oceans or the atmosphere (can also happen at continental rift zones).
-At divergent plate boundaries, magma is rich in deep mantle sources of carbon, and so at the point of eruption lots of CO2 is released
-CO2 is also vented at hotspots and currently inactive volcanoes (e.g. Yellowstone) where CO2 passively diffuses into the atmosphere

Negative feedback cycle: temperature rises from increased CO2 as a result of volcanic outgassing = more acid rain = chemical weathering of rocks = carbon rich rocks like limestone forming in the ocean

Question 28

What is the role that the ocean plays in the carbon cycle? What are the role of pumps?

Answer 28

The ocean is one of the most significant carbon stores on the planet. The ocean has three important pump mechanisms that are fundamental in its role as a key store of carbon. The biological pump, the carbonate pump and the physical pump.

Question 29

What is the function of the ocean’s ‘biological pump’ in the carbon cycle?

Answer 29

-The biological pump sequesters carbon from the atmosphere via photosynthesis from the growth of phytoplanktons
-These carbon rich phytoplanktons form the basis of the ocean food web, as they are passed up the food chain by consumer fish and zooplankton. As a result carbon is returned to the oceans and the atmosphere by the respiration of marine animals, some of the CO2 released is vented out to the air above, and by the biological decay of consumers in this food web
-Phytoplankton sequester over 2 billion tonnes of CO2 into the deep ocean every year

It takes place on a timescale of hours to years.

Question 30

What is the function of the ocean’s ‘carbonate pump’ in the carbon cycle?

Answer 30

The carbonate pump is when dead organic matter, e.g. dead shells and phytoplankton, sinks to the ocean floor and becomes sediment.
-The dead organic matter will eventually become carbonate rocks like limestone (geological carbon store) due to compression from water over a timescale of millions of years.

Only a small proportion of carbon enters the carbon pump.

Question 31

What is the function of the ocean’s ‘physical pump’ in the carbon cycle?

Answer 31

The physical pump moves carbon vertically and horizontally via ocean currents and the thermohaline circulation,
-E.g. major currents such as the Gulf Stream, moves water from the tropics to the poles, the water cools towards the poles and can subsequently absorb more atmospheric CO2
-This is because high latitude and Arctic zones with deep oceans have cooler water which sinks because of its higher density than warm water.
-This takes the CO2 accumulated at the surface downwards to the deep ocean.

Question 32

What is the roles of terrestrial primary producers and consumers in the carbon cycle?

Answer 32

-Terrestrial primary producers - green plants - use solar energy to produce biomass (plant matter), of which 95% of green plants, like trees’, biomass is made up of CO2 whether it be the leaves or roots. CO2 is absorbed and converted into new plant growth during photosynthesis through carbon fixation. As plants grow the CO2 is then released back into the atmosphere through respiration.

-Primary consumers, such as bugs, beetles, larvae and herbivores, depend and feed on producers. Through respiration they return carbon to the atmosphere. Organisms known as biological decomposers, such as insects, worms and bacteria feed on dead plants, animals and waste. (Decomposition fastest in tropical areas due to higher rainfall, temperatures and oxygen levels)

Primary producers - plants - mainly take the role of absorbing atmospheric carbon via photosynthesis, primary consumers - herbivores - mainly take the role of returning carbon to the atmosphere via respiration.

Question 33

What is photosynthesis?

Answer 33

The use of energy from sunlight to produce plant biomass from CO2 and water.

Question 34

What is the role of soil in the carbon cycle?

Answer 34

Soils store 20-30% of global carbon, sequestering about twice the quantity of carbon as the atmosphere and three times that of terrestrial vegetation. However, it depends on local conditions whether it actually sequesters or emits CO2.

The source of carbon in arid and semi-arid soils is often inorganic carbon from limestone or similar carbonate rocks. However, the most important source of carbon in soils is organic carbon, carbon from carbon rich plants, or even just their leaves and branches, that have since decomposed on and below the surface. Decomposition rates vary greatly by climatic conditions and types of soil, whole cycle is very slow in tundra regions. Carbon cycling and formation is most active in the topsoil area, stabilised carbon with longer turnover times in the cycle are located much deeper, particularly in permafrost regions.

Question 35

What factors determine the capacity of soil to store organic soil?

Answer 35

-Climate. It dictates plant growth, microorganism and detritivore (animals that feed on dead organic material) activity, places with high rainfall have an increased potential carbon storage than the same soil exposed to less rainfall
-Soil type. Clay rich soils have a higher carbon content than sandy soils as clay protects carbon from full decomposition.
-Management and use of soils. Since the Industrial Revolution and urbanisation, soils globally have lost 40-90 gigatonnes of carbon through disturbance and cultivation.

Question 36

How does rising atmospheric CO2 have an indirect effect on the carbon dynamics and stability of soils?

Answer 36

It affects vegetation and litter stores and flows. E.g. arctic biome contains 1/3 of the Earth’s soil but with a rapidly warming climate and rising CO2, its net storage function could flip from a store to a source of carbon.

Question 37

How does the natural greenhouse effect operate?

Answer 37

-Short wave solar radiation passes through the atmosphere
-Some short wave radiation is absorbed and is converted into long wave radiation
-Some long wave radiation passes back into space
-Some long wave radiation is reflected off the o-zone, layer made up of greenhouse gasses, back to earth, heating earth up

Question 38

How does the enhanced greenhouse effect operate?

Answer 38

The same process happens but with less long wave radiation passing back into space, instead, due to a thickened o-zone layer as a result of high rates of greenhouse emissions from earth, more significantly more long wave radiation is reflected off the o-zone layer back to Earth heating Earth up.

The thickened o-zone post-industrial revolution is approximately 89% CO2, 7% Methane, 35% Nitrus Oxide and 1% Halocarbons.

Question 39

How is temperature different across the globe as a result of solar radiation?

Answer 39

The amount of solar energy reaching the Earth’s surface varies at different locations, which in turn influences temperature.
-The angle of the sun’s rays makes solar insolation intense at the equator, but dispersed over a wider area at the poles.
-Different characteristics of the Earth’s surface also affect how much heat is absorbed or reflected through the albedo effect, e.g. snow reflects heat as it is light and bright and dark forests absorb heat.
-Heat is redistributed around the globe by air movement (wind) as a result of pressure differences, but also by ocean currents (Gulf Stream moves heat to high latitudes in North Western Europe making Norway, The UK and Iceland milder than other areas of the same latitude.

Question 40

How is precipitation different across the globe as a result of solar radiation?

Answer 40

The heating of the Earth’s atmosphere and surface controls the moisture content of the air among other things. Warm air rises and cools, leading water vapour to condense and clouds to form.
-Solar radiation is most intense over the Equator, convectional rainfall and low pressure systems subsequently dominate there and rainfall is high all year.
-As the air pressure rises around 30 degrees N and S of the equator, precipitation decreases and clouds rarely form
-In mid latitudes (nearly all of Europe, the USA, China, Argentina…) air masses of different characteristics meet and low pressure systems bring rainfall.

Question 41

What is the significance of permafrost soils in the carbon cycle?

Answer 41

-Over 61% of carbon stored deeper than 30cm
-When soil is frozen into permafrost, or when the active layer freezes in the winter (means no microbe activity in surface layer in winter), carbon is locked into the icy store so carbon is contained meaning in permafrost it can be trapped for hundreds of thousands of years

Question 42

What is the significance of mangroves in the carbon cycle?

Answer 42

-Contain vital producers (sequester over 1 tonne of carbon per hectare per year)
-Carbon rich soil with thick organic layers of litter, humus and peat
-Soils are anaerobic as have to cope with submersion at high tide twice a day
-Decomposition is slow and so little carbon can respire back into atmosphere, this is because bacteria and microbes cannot survive without oxygen
-Undisturbed mangroves absorb largest amounts of carbon
-If drained or cleared for tourism, shrimp am aquatic life will form which would lead to respiration and carbon released back into atmosphere

Question 43

What is the approximate composition of the O-zone post-industrial revolution?

Answer 43

The thickened o-zone post-industrial revolution is approximately 89% CO2, 7% Methane, 35% Nitrus Oxide and 1% Halocarbons.

Question 44

What is the importance of carbon for soils?

Answer 44

-Carbon is vital for soils.
-Organic material is the medium by which carbon passes through the system and it supports micro-organisms that maintain the nutrient cycles, break down organic matter, provide pore spaces for infiltration and water storage (CO2 needed for plant growth such as roots which help create more infiltratable soil), and enhance plant growth
-Without carbon nutrient and water cycles cannot operate properly

Question 45

How do you work out the amount of organic carbon stored in soil? (inputs and outputs)

Answer 45

Inputs (plant litter, animal waste…) MINUS outputs (decomposition, erosion, uptake in plant growth…)

Question 46

What does carbon stored in soils lead to productivity wise?

Answer 46

Stored carbon = healthy soils = high primary productivity

Question 47

How can you tell if soil is healthy?

Answer 47

-Dark, crumbly, porous (enables infiltration and percolation so are more resilient to wetter weather)
-Retain moisture (regulates soil moisture/temp during heatwaves and droughts)
-Sequester more carbon (positive feedback cycle as more carbon stored = healthier soils)

Question 48

What does primary productivity mean?

Answer 48

The rate in which plants produce biomass. Warm, humid and year round growth rainforest biomes have highest productivity - cold and dry tundra ecosystems have slower growth and lower productivity.

Healthier soil due to more carbon storage = generally more primary productivity.