1. Carbon cycle processes/stores

Question 1

What are the major stores of carbon?

Answer 1

• Lithosphere: sedimentary rock and fossil fuel deposits
• Hydrosphere: Phytoplankton at surface, ocean floor sediment, shells of marine organisms
• Biosphere: Organic matter in soils, living/dead organisms
• Atmosphere: CO2 makes up 0.004% of atmosphere

Question 2

What is the major long-term store of carbon on Earth?

Answer 2

99% of all long-term stored carbon on earth is held in sedimentary rocks (60,000,000 Gt)
Held for 150 million years

Question 3

How much carbon does the atmosphere store?

Answer 3

600Gt

Held for 6 years

Question 4

Describe photosynthesis:

Answer 4

Process by which plants convert water and CO2 into starch and sugar in the presence of sunlight

Question 5

Describe respiration:

Answer 5

Process in living organisms where the intake of oxygen oxidises organic substances to produce energy and release CO2

Question 6

Describe oxidation:

Answer 6

A chemical process that weathers certain types of rock and involves the absorption of oxygen

Question 7

Describe weathering:

Answer 7

The breakdown of rocks exposed at, or near, the land surface by physical, chemical, and biological processes

Question 8

What are the two strands to the carbon cycle?

Answer 8

Slow carbon cycle and the fast carbon cycle

Question 9

Where is carbon stored in the slow carbon cycle?

Answer 9

Rocks, sea floor sediments and fossil fuels

Question 10

How much carbon is circulated by the slow carbon cycle?

Answer 10

100 million tonnes per year

Question 11

How do sea-floor sediments accumulate?

Answer 11

1. CO2 from the atmosphere diffuses into the oceans – marine organisms fix the carbon into shells to form calcium carbonate
2. When marine animals die, shells sink to ocean floor and accumulate
3. Over millions of years, due to heat and pressure, they are converted into carbon-rich rocks

Question 12

How is carbon released during the slow carbon cycle?

Answer 12

1. Carbon-rich sedimentary rocks that are subducted into the mantle at plate boundaries are released during volcanic eruptions
2. Chemical weathering: carbonation = precipitation containing CO2 forms a weak acid which dissolves carbonate minerals in rocks, releasing CO2 into atmosphere and via rivers/streams

Question 13

What are carbonaceous rocks?

Answer 13

Partly decomposed organic material on land that is buried beneath younger sediment
Eg Coal, oil, natural gas

Question 14

What is the fast carbon cycle?

Answer 14

The uptake of CO2 from the atmosphere by plants during photosynthesis and the release of CO2 back into atmosphere via respiration/decomposition

Question 15

How much quicker is the fast carbon cycle than the slow carbon cycle?

Answer 15

Between 10 and 1000 times quicker

Question 16

What are the key components of the fast carbon cycle?

Answer 16

Plants and phytoplankton

Question 17

What are phytoplankton?

Answer 17

Tiny photosynthesising marine organisms on the surface waters of the ocean

Question 18

Components of the fast carbon cycle x4:

Answer 18

Photosynthesis by plants and phytoplankton = carbon absorbed
Respiration by plants and animals = carbon returned to atmosphere
Decomposition by microbes = carbon returned to atmosphere
Dissolvement of CO2 from atmosphere into oceans and vice versa

Question 19

What are the processes of the carbon cycle x7?

Answer 19

• Precipitation
• Photosynthesis
• Respiration
• Decomposition
• Combustion
• Carbon sequestration in oceans and sediments
• Weathering

Question 20

Describe how precipitation is a process in the carbon cycle:

Answer 20

Atmospheric CO2 dissolves in rainwater to form a weak carbonic acid
Acidity of rainfall has increased due to rising anthropogenic emissions of carbon

Question 21

Describe how photosynthesis is a process in the carbon cycle:

Answer 21

Plants use energy from sunlight and combine CO2 from the atmosphere with water to form carbohydrates
Carbon can be sequestered in plants for long time periods

Question 22

Describe how respiration is a process in the carbon cycle:

Answer 22

Plants/microscopic organisms release CO2 back into atmosphere

Question 23

Describe how decomposition is a process in the carbon cycle:

Answer 23

Fungi and bacteria return CO2 into the atmosphere (as well as GHG)

Question 24

Describe how combustion is a process in the carbon cycle:

Answer 24

Occurs when organic matter burns in the presence of oxygen
Two types:
1. Natural use = wildfires caused by lightning strikes are essential for the health of ecosystems eg coniferous forests of the Rocky mountains
2. Fossil fuel use = (gas, oil etc) contain carbon captured by living organisms over periods of millions of years and since the industrial revolution these have been mined and combusted to produce energy = release CO2 back into atmosphere

Question 25

Describe how carbon sequestration is a process in the carbon cycle:

Answer 25

Sequestration = long-term storage of carbon

• Oceanic carbon pump: at low latitudes warm water absorbs CO2 by diffusion and at higher latitudes, cooler water sinks and transfers carbon to the deep ocean + when it returns to surface and warms, CO2 lost back to atmosphere eg North Atlantic
• Biological carbon pump: Phytoplankton fix carbon through their shells and pass it through food chain and used by shell-building organisms. Once these die they sink and decay releasing CO2 into deep water

Question 26

Describe how weathering is a process in the carbon cycle:

Answer 26

Weathering is the in situ breakdown of rocks at the Earth’s surface by chemical physical and biological processes
- Chemical: carbonic acid in rainwater dissolves limestone and chalk through carbonation
Chemical processes transfer 0.3 billion tonnes of carbon to the atmosphere every year
eg Yorkshire Dales
- Physical: freeze-thaw breaks rocks into smaller particles and increases surface area for chemical weathering
- Biological: chelation - rainwater mixes with dead matter in the soil to form humid acids that attack minerals in the rock eg tropical environments