3.1.1.3 The Carbon Cycle

Question 1

What is the Lithosphere and where is carbon stored in it?

Answer 1

The Lithosphere is the rock shell of the earths surface.

Carbon is stored in:

• Sedimentary rocks (60-100 million Gt)
• Fossil fuel deposits (4,130 Gt)

Question 2

What is a Gt?

Answer 2

Gt (gigatonnes, 1 Gt = 1 billion tonnes)

Question 3

What is the Hydrosphere and where is carbon stored in it?

Answer 3

The Hydrosphere is all of the water existing on earth.

Carbon is stored in:

• Ocean surface layer (700 Gt)
• Ocean deep layer (38,000 Gt)

Question 4

What is the Biosphere and where is carbon stored in it?

Answer 4

The Biosphere is the zone of all living things on earth.

Carbon is stored in:

• Soil (2,300 Gt)
• Terrestrial Biomass (560 Gt)

Question 5

What is the Atmosphere and where is carbon stored in it?

Answer 5

The Atmosphere is the blanket of all the air that surrounds the earths surface.

Carbon is stored in:

• Atmosphere (600 Gt)

Question 6

Processes driving the transfer of carbon

Answer 6

• Photosynthesis
• Respiration
• Decomposition
• Combustion
• Carbon Sequestration
• Weathering

Question 7

Carbon Sequestration

Answer 7

Is the process of storing carbon from the atmosphere in a solid or liquid form.

It can be natural…

• oceanic carbon pump
• biological carbon pump

… or artificial.

Question 8

Oceanic Carbon Pump

Answer 8

CO2 goes from the atmosphere to the ocean through the process of diffusion.

At low latitudes, warm water absorbs the CO2.

At high latitudes, the cold water sinks and the carbon is transferred into the deep ocean.

Where cold water returns to the surface and warms again, the CO2 is lost to the atmosphere.

Question 9

Biological Pump

Answer 9

Phytoplankton fix CO2 through photosynthesis.

Carbon therefore passes through the oceanic food web.

Shell building organisms remove carbonate from the sea.

When these organisms die, the shell sinks to the deep water and the decay of the organism releases some CO2 too. (biological pump)

Some material from the shell forms layers of carbon-rich sediment which over millions of years turn to sediment in rocks.

Question 10

Manmade Carbon Sequestration

Answer 10

Carbon capture and storage (CCS) is a technology that can capture 90% of CO2 emissions produced from the use of fossil fuels.

It is broken down into 3 parts:

• Capture (technology separates CO2 from gases)
• Transporting ( CO2 is transported through pipelines or ships)
• Storage (the CO2 is securely stored underground, depleted oil and gas fields)

Question 11

How do wildfires affect the carbon cycle

Answer 11

Transfer carbon from biosphere to atmosphere as CO2 is released through burning.

Also exposes soil, which releases carbon from decaying plant matter.

Can encourage the growth of plants in the long term.

Question 12

How does volcanic activity affect the carbon cycle

Answer 12

Carbon stored within the earth is released during volcanic eruptions, mainly
as CO2 gas.

However sulphur dioxide is also released into the upper atmosphere blocking solar radiation.

Particles of ash and dust can also cause temporary cooling.

This leads to both affects countering each other and therefore the affect of volcanic activity is uncertain.

Question 13

How does farming practices affect the carbon cycle

Answer 13

Arable farming releases CO2 as animals respire.

Ploughing can release CO2 stored in the soil.

Farm machinery such as tractors may release CO2.

Question 14

How does fuel combustion affect the carbon cycle

Answer 14

Combustion transfers CO2 to the atmosphere from a long-term carbon sink

Question 15

How does deforestation affect the carbon cycle

Answer 15

Often used to clear land for farming/housing, rapidly releases carbon stored in plants using slash and burn techniques and interrupting the forest carbon cycle.

Question 16

How does land use changes affect the carbon cycle

Answer 16

Urban growth reduces the amount of surface vegetation. CO2 emissions increase due to higher levels of energy consumption. Increase in CO2 emissions from cement manufacturing which is required for more building.

Question 17

Carbon Budget

Answer 17

The Carbon Budget is the balance between carbon inputs and outputs to a store at any scale.

Question 18

Carbon Source

Answer 18

A store that emits more carbon than it absorbs.

Question 19

Carbon Sink

Answer 19

A store that absorbs more carbon than it emits.

Question 20

Positive Feedback Loops in carbon cycle (three)

Answer 20

• Wildfires are more likely in hotter and drier climates due to global warming, which release large quantities of CO2 into atmosphere, which in turn then increases the warming effect)
• Albedo feedback (Ice reflects radiation from the sun, reducing surface warming. As sea temperatures rise and ice melts, the warming effect is amplified as there is less ice to reflect the radiation. Further melting occurs and the process continues). Ice has a high albedo.
• Higher temperatures are thawing the permafrost releasing CO2 and methane (which has 20 times the warming effect of CO2), causing warming on a local and global scale. The higher temperatures cause more permafrost to melt, causing further gas releases and further warming.

Question 21

Negative Feedback Loops in the carbon cycle (three)

Answer 21

• Increased photosynthesis by plants and rising global temperatures allows vegetation to grow in new areas, e.g. where permafrost has melted. New vegetation absorbs CO2 from the atmosphere, decreasing the warming effect.
• Higher temperatures and more CO2 cause a greater carbon fertilisation in plants, so they absorb more CO2, reducing the levels of CO2 and the rates of warming and then the carbon fertilisation, if temperatures decline. The process repeats.
• Phytoplankton photosynthesise to gain energy and warmer oceans and more sunlight due to climate change boost this and the production of a chemical by the plankton which causes cloud formation. Increased cloud cover decreases warming by the sun and more photosynthesis reduces CO2 levels, reducing the levels of warming. The plankton grow less quickly and less of the chemical is increased decreasing cloud cover. The cycle continues.

Question 22

Outline the process of decomposition in the carbon cycle

Answer 22

Decomposition refers to the breakdown / decay of organic matter by bacteria or fungi.

During decomposition carbon dioxide is released.

Most of the carbon released into the atmosphere is as a result of decomposition.

Decomposition is heavily temperature dependent, with warmer climates characterised with much higher rates of decomposition.

Question 23

Outline the process of photosynthesis in the carbon cycle

Answer 23

Photosynthesis transfers carbon stored in the atmosphere to biomass.

Plants and phytoplankton use energy from the sun to change carbon dioxide and water into glucose and oxygen.

This enables plants to grow.

Carbon is passed through the food chain and released through respiration and decomposition.

Question 24

Outline the process of respiration in the carbon cycle

Answer 24

Respiration transfers carbon from living organisms to the atmosphere.

Plants and animals break down glucose for energy, releasing carbon dioxide and methane in the process.

Question 25

Outline the process of combustion in the carbon cycle

Answer 25

Combustion transfers carbon stored in living dead or decomposed biomass to the atmosphere by burning.

Wildfires cause carbon flow.

Question 26

Outline the process of weathering in the carbon cycle

Answer 26

Chemical weathering transfers from the atmosphere to the biosphere and hydrosphere.

Atmospheric carbon reacts with water vapour to form acid rain.

When this falls on rocks a chemical reaction occurs which dissolves the rocks.