Enquiry Question 1: How does the carbon cycle operate to maintain planetary health?

Question 1

Why is carbon important to life?

Answer 1

• Carbon is the main building block of life
• It is stored in many things, each store can be referred to as a store or reservoir: the atmosphere (e.g. carbon dioxide, methane), the hydrosphere (e.g. dissolved carbon), the lithosphere (e.g. carbonates in limestone and fossil fuels such as coal, oil and gas), and the biosphere (in both living and dead organisms)
• Carbon moves from one sphere to another through the carbon cycle

Question 2

Store/Reservoir

Answer 2

Where the carbon is held

Question 3

Fluxes

Answer 3

The flows of movement between the stores, which can operate at local and global scales

Question 4

Petagrams (Pg)/Gigatonnes (Gt)

Answer 4

The units used to measure carbon; one petagram (Pg), also known as a gigatonne (Gt), is equal to a trillion kilograms, or 1 billion tonnes

Question 5

What are the two types of carbon?

Answer 5

• Geological carbon

- Biologically derived carbon

Question 6

How is geological carbon formed?

Answer 6

• Geological carbon is formed when rocks such as sedimentary rocks are created e.g. limestone and chalk
• One of earth’s largest stores of carbon is the Himalayas which started off as oceanic sediments rich in calcium- this is now being weathered and returned back to the oceans

Question 7

How is biological carbon formed?

Answer 7

• Biologically derived carbon is created from dead organisms such as coal and shale
  1. Before the dinosaurs, many giant plants died in swamps
  2. Over millions of years, the plants were buried under water and dirt
  3. Heat and pressure turned the dead plants into coal

Question 8

Example of a process which moves carbon around?

Answer 8

Photosynthesis

Question 9

Positive and negative feedback

Answer 9

• If sources equal sinks = the carbon cycle is balanced, or there is an equilibrium
• If the cycle is unbalanced then this results in a positive or a negative feedback
• Positive (amplifying) feedback loops occur when a small change in one component causes changes in other components. This shifts the system away from its previous state and towards a new one
• Earth systems normally operate by negative (stabilising) feedbacks, maintaining a stable state by preventing the system moving beyond certain thresholds. I.e. any change is cancelled out, maintaining equilibrium

Question 10

What’s the difference between a source and a sink?

Answer 10

A source adds carbon to the atmosphere and a sink removes carbon from the atmosphere

Question 11

Examples of carbon sources

Answer 11

Volcanoes, glaciers, combustion(?)

Question 12

Examples of carbon sinks

Answer 12

Oceans, forests, soil, photosynthesis of plants(?)

Question 13

Bio-geochemical carbon cycle

Answer 13

• Biological and chemical processes determine just how much of the carbon available on the Earth’s surface is stored or released at any one time.
• The role of living organisms are critical to the cycle and to controlling the balance between overall storage, release, transfer and absorption of carbon.
• Four key processes are:​ photosynthesis​, respiration​decomposition​ and combustion​​

Question 14

Respiration

Answer 14

A chemical process that happens in all cells and is common to both plants and animals. Glucose is converted into energy that can be used for growth and repair, movement and control of body temperature in mammals. Carbon dioxide is then returned to the atmosphere, mostly by exhaled air

Question 15

Decomposition

Answer 15

When organisms die they are consumed by decomposers such as bacteria, fungi and earthworms. During this process of decomposition, carbon from their bodies is returned to the atmosphere as carbon dioxide. Some organic material passes into the soil where it may be stored for hundreds of years

Question 16

Combustion

Answer 16

Organic material contains carbon. When it is burned in the presence of oxygen (e.g. coal in a power station) it is converted into energy, carbon dioxide and water. This is combustion. The carbon dioxide is released into the atmosphere, returning carbon that might have been stored in rocks for millions of years

Question 17

Photosynthesis

Answer 17

• This is the process whereby plants use the light energy from the sun to produce carbohydrates in the form of glucose
  1. Green leaves absorb the light energy using chlorophyll (a green substance found in chloroplasts in plant cells) in their leaves
  2. The absorbed energy converts carbon dioxide in the air and water from the soil into glucose. During this process, oxygen is released into the air
  3. Some glucose is used in respiration, the rest is converted into starch, which is insoluble but can be converted back into glucose for respiration
• Carbon dioxide + water → glucose + water
• (→ = light energy)

Question 18

Explain the importance of fluxes to the carbon cycle (6)

Answer 18

One way that fluxes are important to the carbon cycle is that they keep the cycle balanced. Fluxes process carbon through different reservoirs, allowing the carbon cycle to be balanced. For example, carbon is released into the atmosphere through processes such as respiration which can be around 60Pg per year and absorbed from the atmosphere through ocean uptake, around 92Pg per year. This makes them important as without these fluxes moving carbon around we would have more carbon in particular reservoirs which means that positive feedback loops could potentially be initiated.

A second reason why fluxes are important to the carbon cycle is that they can store carbon away for long periods of time. Fluxes such as ocean uptake and burial to sediments can store large amounts of carbon for decades and even hundreds of years. For example, the Earth’s crust stores around 100,000,000Pg. Having carbon be processed through these fluxes means that particular reservoirs in the cycle don’t be come overloaded which means that the cycle remains in equilibrium.

Question 19

Crustal/terrestrial/ geological

Answer 19

• Store type = Sedimentary rocks, very slow cycling over millennia
• Petagrams average (PgC) = 100,000,000 fossil fuels store an extra 4,000

Question 20

Oceanic (deep)

Answer 20

• Store type = Most carbon is dissolved, inorganic carbon stored at great depths, very slowly cycled
• Petagrams average (PgC) = 38,000

Question 21

Terrestrial soil

Answer 21

• Store type = From plant materials (biomass) microorganisms break most organic matter down into C02 in a process which can take days in a hot and humid climate to decades in colder climates
• Petagrams average (PgC) = 1,500

Question 22

Oceanic (surface)

Answer 22

• Store type = Exchanges are rapid with the atmosphere through physical processes such as C02 dissolving in the water and biological processes involving plankton. Some of this carbon sinks into the deeper ocean pool
• Petagrams average (PgC) = 1,000

Question 23

Atmospheric

Answer 23

• Store type = C02 and CH4 store carbon as greenhouse gases with a lifetime up to 1
• Petagrams average (PgC) = 560

Question 24

Terrestrial ecosystems

Answer 24

• Store type = CO2 is taken from the atmosphere by photosynthesis, carbon is stored organically, especially in trees. Rapid exchange with the atmosphere- seconds/minutes
• Petagrams average (PgC) = 560

Question 25

Geological carbon cycle

Answer 25

The ‘Geological Carbon Cycle’ refers to the natural cycle that moves carbon between land, oceans and the atmosphere. The movement involves a number of chemical reactions (the bio-geochemical cycle e.g. photosynthesis

Question 26

Mechanical weathering

Answer 26

The breakup of rocks by frost ; shattering and exfoliation produces small, easy-to-transport particles

Question 27

Chemical weathering

Answer 27

The breakdown of rocks by carbonic acid in rain, which dissolves carbonate-based rocks

Question 28

Biological weathering

Answer 28

Burrowing animals and the roots of plants can break rocks up

Question 29

Transportation

Answer 29

Rivers carry particles (ions) to the ocean, where they’re deposited

Question 30

Sedimentation

Answer 30

Over millennia these sediments accumulate, burying older sediments below, such as shale and limestone

Question 31

Metamorphosis

Answer 31

The layering and burial of sediments causes pressure to build, which eventually becomes so great that deeper sediments are changed into rock; shale becomes slate and limestone becomes marble

Question 32

What percentage of carbon-containing rocks is from shell-building (calcifying) organisms (coral) and plankton?

Answer 32

• 80%

- The remaining 20% of rocks contain organic carbon from organisms that have been embedded in layers of mud

Question 33

The geological part of the carbon cycle interacts with the rock cycle in 5 key phases:​

Answer 33

1. Chemical weathering​
2. Transportation of calcium ions by rivers​
3. Deposition and burial = limestone formation​
4. Subduction of the sea floor​
5. Degassing of volcanoes restores carbon to the atmosphere

Question 34

Geological carbon release

Answer 34

• Volcanic activity releases about 300 million tonnes of CO2 per year. Mount Etna is the most actively degassing volcano in Europe due to the limestone and dolomite rocks beneath
• Degassing takes place through the main vent of a volcano, hot spot and at constructive plate margins
• Carbon is recycled at destructive plate margins when carbonate rocks are dragged into the mantle creating an upper mantle carbon concentration of between 50 and 250ppm

Question 35

Explain how carbon is released into the atmosphere through volcanic eruptions and plate boundary processes (6 marks)

Answer 35

Volcanic eruptions are one way carbon is released into the atmosphere. The Earth’s crust can be up to 50km thick and as such is the biggest carbon store, storing an average of 100,000,000 petagrams of carbon. As carbon rises to the surface, degassing (or outgassing) takes place which means that carbon is released into the atmosphere. This can take place through the main vent, a hot spot or constructive margin.

Plate boundary processes support volcanic outgassing by the subduction of the sea floor. For example, at a constructive plate margin such as the Mid-Atlantic Ridge, the oceanic crusts are drawn apart. The carbon stored in the mantle and deeper subducted plates is able to rise through the gap which means that the carbon is released into the atmosphere. An example of this is the eruption of the Eyjafjallajökull eruption in 2010, which released 150,000-300,000 tonnes of carbon each day.

Question 36

The ocean as a carbon sink

Answer 36

• The ocean’s are one of the Earth’s largest store, being 50 times greater than the atmosphere.
• 93% of CO2 is stored in undersea algae, plants and coral, with the remainder dissolved in the water

Question 37

Biological pump

Answer 37

• This is the sequestration of C02 to oceans by phytoplankton. Phytoplankton float on the surface of the ocean to access sunlight and photosynthesise. They are autotrophs and are the base of the marine food web. Even though they are minute, they make up over half the planets biomass
• Carbon is then passed up the food chain by consumers which in turn release C02 back to the atmosphere.
• In this way most carbon is cycled in surface waters and only 0.1% reaches the sea floor through decompositions and sedimentation
• Phytoplankton sequester over 2 billion metric tonnes of C02 annually to the deep ocean
• In total, the processes transfer between 5-15 gigatonnes of carbon from the atmosphere to the deep ocean each year

Question 38

Carbonate pump

Answer 38

• Part of the biological pump, the carbonate pump is crucial as it pumps CO2 out of the atmosphere and into the ocean store
• This relies on inorganic carbon sedimentation. Lots of marine organisms utilise calcium carbonate to make their outer shells/skeletons. When these organisms die and sink to the sea floor many shells will dissolve on the way and the carbon will become part of the ocean and flow around the planet in currents. Shells that do not dissolve build up slowly on the sea floor forming limestone sediments, such as those in the white cliffs of Dover

Question 39

Physical pump

Answer 39

• Also known as the thermohaline circulation is an ocean current which produces vertical and horizontal circulations of warm and cold water around the world’s oceans
• This oceanic circulation of water includes upwelling and down welling
• C02 in the oceans is mixed much slower than in the atmosphere so there are large spatial differences in concentration
• Colder water can absorb more C02 so C02 concentration is 10% higher in the deep ocean than the surface and polar regions store more than tropical regions
• Warm waters release C02 into the atmosphere and cold waters absorb C02
• Warm surface water is depleted of nutrients and carbon dioxide, but they are enriched again as they travel through the conveyor belt as deep/bottom layers
• The circulation helps shift carbon in the carbonate pump cycle from upper to deeper waters
• Large ocean currents like the North Atlantic Drift move water from the tropics to the poles, the water cools and absorbs more C02.

Question 40

Upwelling

Answer 40

An instance or amount of seawater, magma, or other liquid rising up

Question 41

Downwelling

Answer 41

The downward movement of fluid, especially in the sea, the atmosphere, or deep in the earth

Question 42

Inorganic

Answer 42

Not consisting of or deriving from living matter

Question 43

Authotroph

Answer 43

An animal capable of producing its own food

Question 44

Physical pump - current travel

Answer 44

1. The main current begins in polar oceans where the water gets very cold; sea ice forms; surrounding seawater gets saltier; increases in density and then sinks
2. The current is recharged as it passes Antarctica by extra cold salty, dense water
3. Division of the main current: northward into the Indian Ocean and into the western Pacific
4. The two branches warm and rise as they travel northward, then loop back southward and westward
5. The now-warmed surface waters continue circulating around the globe. On their eventual return to the North Atlantic, they cool and the cycle begins again

Question 45

Role of phytoplankon

Answer 45

• Phytoplankton float on the ocean’s surface to access sunlight and photosynthesise
• Despite their size they make up half of the planet’s biomass
• They absorb carbon, when eaten that carbon is passed along the food chain
• Part of that carbon is released through respiration
• Some carbon reaches the sea floor through decomposition and sedimentation
• Threatened by warming oceans

Question 46

Variations in plankton

Answer 46

• Thrive along coastlines and continental shelves
• Found along the equator in the Pacific and Atlantic Oceans
• Thrive in high latitude areas
  THIS IS BECAUSE:
• Oceans rich in nutrients from deep water upwelling
• In high latitudes blooms peak in spring and summer when sunlight increases
• In subtropical oceans blooms decrease because surface waters warm up and become buoyant, with cold, dense water below the water doesn’t mix easily, meaning nutrients are quickly used up

Question 47

What is the fastest part of the carbon cycle?

Answer 47

Terrestrial sequestration is the fastest part of the carbon cycle

Question 48

Globally, what are the most productive biomes?

Answer 48

Globally, the most productive biomes are tropical forests, savannah and grasslands

Question 49

Terrestrial sequestration process

Answer 49

1. Primary producers (plants) take in carbon through photosynthesis and then release CO2 back into the atmosphere through respiration
2. Consumer animals then eat these plants and absorb the carbon which becomes part of its fats and proteins.
3. Initially after the animal has died, microorganisms and detritus feeders such as beetles feed on waste material which becomes part of these micro-organisms
4. After death, tissues decay into the soils. This process is affected by climate and decomposition will happen fastest in tropical climates (warm and damp) or, in Arctic biomes, the process can be ‘locked down’ for substantial time periods

Question 50

Explain how carbon enters and exits the biosphere (4)

Answer 50

One way carbon enters the biosphere is through photosynthesis (1). Plants absorb and use atmospheric carbon which means that it enters the biosphere (1).
One way carbon can exit the biosphere is through animals (1). If an animal consumes the plant, then the carbon that the animal absorbs becomes part of their fat and protein which means that once that animal has died and decomposed the carbon will be released (1).

Question 51

Soils

Answer 51

Soils store 20-30% of global carbon, sequestering about twice the quantity of carbon as the atmosphere and three times that of terrestrial vegetation. Whether the soil sequesters or emits C02 depends on local conditions

Question 52

Factors effecting carbon sequestration in soils

Answer 52

1. Climate - This dictates plant growth and microbe activity. Rapid decomposition occurs at higher temperatures or under water logged conditions. Places with high rainfall have an increased potential carbon storage than the same soil type in lower rainfall places. Arid soils store only 30 tonnes per hectare compared with 800 tonnes per hectare in cold regions
2. Soil type - Clay-rich soils have a higher carbon content than sandy soils as clay protects carbon from decomposition
3. Management and use of soils - Since 1850, soils globally have lost 40-90 billion gigatons of carbon through cultivation and disturbance. Current rates of carbon loss due to land-use change are 1.6 ± 0.8 billion gigatons of carbon per year

Question 53

Explain the factors that affect the storage of carbon in soils (6)

Answer 53

One factor that affects the storage of carbon in soil is climate. For example, arid soils store 30 tonnes of carbon on average per hectare, in comparison to 800 tonnes per hectare for cold regions. This affects the storage of carbon because the temperature can affect the level of microbe activity taking place which means that in hotter regions rapid decomposition occurs, releasing the carbon stored.

A second factor that affects the storage of carbon in soil is the management and use of it. For example, since 1850 globally soils have lost between 40-90 billion gigatons of carbon. This affects the storage as activities such as cultivation disturbs the soil which means that more of it is exposed to warmer temperatures meaning higher rates of decomposition takes place.

Question 54

The enhanced greenhouse gas effect

Answer 54

• 31% of short wave radiation is reflected by clouds, aerosols and gases in the atmosphere and by the land surface
• The remaining 69% is absorbed, particularly by the oceans
• When long wave radiation is reflected back, a large amount is re-radiated back to Earth by clouds and GHGs which traps the long wave radiation in our atmosphere
• The natural greenhouse effect and gives us our life supporting average temperature of 15 degrees. Without this effect our average temperature would be -6

Question 55

Why is it called the ‘enhanced’ ghg effect?

Answer 55

The natural greenhouse effect has become enhanced; C02 in the atmosphere has increased in volume by 40% in the last 300 years

Question 56

Cement production

Answer 56

The most consumed product in the world after water.

Chemical processes involved in production release a substantial amount of carbon dioxide (6% of global carbon emissions)

Question 57

Wetland/peatland loss

Answer 57

The nature of wetlands is shaped by water and rainfall patterns – the unpredictable change due to climate change may result in wetlands drying out.
Peatlands store 550Gt of carbon – twice as much as all of the world’s forest biomass combined but only cover 3% of the earth’s surface

Question 58

Causes of GHGs

Answer 58

• Agriculture - livestock = methane, deforestation = farmland, loss of soil carbon from ploughing
• Industry - combustion of fossil fuels
• Transport - carbon dioxide emissions
• Electricity generation - increased demand due to rising population
• Cement production
• Wetland/peatland loss

Question 59

Human activity

Answer 59

• Through burning fossil fuels we have transferred considerable amounts of carbon from fossil stores, where exchanges are very slow, into the fast category, significantly disturbing the carbon cycle
• CO2 levels in the atmosphere are higher than ever before
• This process has continued since the Industrial Revolution (1760-1840) and accelerated through the oil age (20th century), changing the chemistry of the atmosphere

Question 60

Temperature - how is it distributed?

Answer 60

• The amount of solar energy (solar insolation) 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 (how light or dark it is) also affects how much heat is absorbed or reflected

Question 61

Precipitation - how is it distributed?

Answer 61

• The heating of the atmosphere and surface controls the temperature, pressure, movement and moisture content of the air
• Because solar radiation is most intense at the equator, low pressure systems dominate there, meaning rainfall all year round
• Regional and seasonal variations also
  occur, because of the effects of relief, pressure patterns and wind systems

Question 62

Levels of CO₂ in the atmosphere today?

Answer 62

They’re now higher than ever before, compared with air bubbles found in ice cores of up to 800,000 years old

Question 63

What does fossil fuel combustion create?

Answer 63

Fast carbon cycling - without it, the carbon in fossil fuels would transfer slowly through volcanic activity

Question 64

The IPCC has estimated that the concentration of CO₂ in the atmosphere between 1750 and 2011 has increased by what percentage?

Answer 64

40%, with approximately 50% of those emissions still in our atmosphere today

Question 65

How many years does carbon remain in the atmosphere?

Answer 65

2000 years

Question 66

How would a 2°C temperature increase affect the climate?

Answer 66

• Thermohaline circulation may weaken (Atlantic and Southern oceans)
• Antarctic ice shelves will melt - adds more freshwater to the Southern ocean, changing density and convection
• Extratropical low-pressure system tracks will move northwards
• Temperate and tropical areas may experience stronger storm activity
• Precipitation will increase in higher latitudes, and decrease in lower ones
• The Sahel, South Africa and Asia, and the Mediterranean will become drier

Question 67

The average arctic temperature has increased how many times at the global average over the past 200 years?

Answer 67

2x

Question 68

How would a 2°C temperature increase affect ecosystems?

Answer 68

• Habitat changes will mean that 10% of land species with limited adaptability will face extinction
• It will affect biodiversity as habitats shift poleward/ into deeper ocean waters/higher altitudes
• Plant changes will lag behind animal changes as they lack mobility
• Acidification of seawater will threaten corals and the shells of marine creatures will get smaller and thinner

Question 69

How would a 2°C temperature increase affect the hydrological cycle?

Answer 69

• Rivers will dry up in regions where precipitation is reduced due to higher evaporation rates
• A shift of subtropical high-pressure areas northwards will cause a 20-30% decrease in water availability in Mediterranean climate
• Small glaciers will disappear, which decreases river discharges
• Humidity levels in the atmosphere will increase
• Extreme precipitation events will become common
• Intense precipitation may result in increased flash flooding
• Permafrost will thaw and add more water to Arctic rivers