Carbon cycle theory

Question 1

what is the biosphere

Answer 1

the regions of the surface and atmosphere of the earth or another planet occupied by living organisms

Question 2

what are carbon stores also known as

Answer 2

carbon sinks

Question 3

what is 99.9% of all carbon storage

Answer 3

99.9% of all carbon storage is in carbonate-based sedimentary rocks

Question 4

what are the two strands to the carbon cycle

Answer 4

a slow cycle and a fast cycle

Question 5

what is the slow carbon cycle

Answer 5

carbon stored in rocks, sea-floor sediments + fossil fuels which is locked away for millions of years

Question 6

what is the total amount of carbon circulated by this slow cycle and how does it work?

Answer 6

• total amount of carbon circulated by this slow cycle is 10-100 million tonnes/year
• CO2 diffuses from the atmosphere into the oceans where marine organisms make their shells + skeletons by fixing dissolved carbon together w calcium carbonate.
• on death, remains of these organisms sink to the ocean floor.
• they accumulate over millions of years, heat and pressure convert them to carbon-rich sedimentary rocks through lithification

Question 7

what is the typical residence time for carbon held in rocks

Answer 7

150 million years

Question 8

what is the fast carbon cycle

Answer 8

carbon circulates most rapidly between the atmosphere, the oceans, living organisms (biosphere) + soils

Question 9

what are the key components of the fast carbon cycle and how does it work

Answer 9

• land plants + microscopic phytoplankton in the oceans are key components
• through photosynthesis, they absorb CO2 from the atmosphere + combine it w water + sunlight to make carbohydrates
• carbon exchange also occurs between the atmosphere + the oceans. through this exchange, individual carbon atoms are stored in the oceans for around 350 years

Question 10

what are the carbon cycle processes

Answer 10

photosynthesis, respiration, precipitation, weathering, decomposition + combustion

Question 11

photosynthesis as a process in the carbon cycle

Answer 11

• the flux of carbon from atmosphere to land plants + phytoplankton via photosynthesis is around 120GT/year

Question 12

what is respiration

Answer 12

• respiration is the process by which carbohydrates fixed in photosynthesis are converted to CO2 + water (reverse of photosynthesis)
• plants + animals absorb oxygen, which ‘burns’ these carbohydrates + provides the energy needed for metabolism + growth

Question 13

what is the word equation for photosynthesis and respiration

Answer 13

carbon dioxide + water glucose + oxygen

Question 14

why is precipitation considered a process of the carbon cycle

Answer 14

atmospheric CO2 dissolves in rainwater to form weak carbonic acid. this is a natural process, however, rising concentrations of CO2 in the atmosphere, due to anthropogenic emissions, have increased the acidity of rainfall. increased acidity in oceans

Question 15

what is weathering

Answer 15

weathering is the in situ breakdown of rocks at/near Earth’s surface by chemical, physical + biological processes

Question 16

why is weathering considered a process of the carbon cycle

Answer 16

rainwater is a weak carbonic acid, which slowly dissolves limestone + chalk in a process known as carbonation. this releases carbon from limestones to streams, rivers, oceans + the atmosphere

Question 17

how much carbon does chemical weathering transfer to the atmosphere + oceans every year

Answer 17

it is estimated that chemical weathering alone transfers 0.3 billion tonnes of carbon to the atmosphere + the ocean/year

Question 18

how does rate of decomposition depend on climatic conditions

Answer 18

rates of decomposition depend on climatic conditions. the fastest rates occur in warm, humid environments, with slow decomposition occurring in cold environments such as Arctic Tundra

Question 19

when does combustion occur

Answer 19

combustion occurs when organic material reacts or burns in the presence of oxygen - combustion process releases CO2 as well as other gases

Question 20

what combustion occurs in ecosystems?

Answer 20

• wildfires caused by lightning strikes are essential to the health of some ecosystems, as long, cold winters slow the decomposition of forest litter which builds up on the forest floor. Fire shifts this log jam, freeing carbon + nutrients previously inaccessible to forest trees.
• it also opens up the forest canopy, creating new habitats + increasing biodiversity.
• combustion also results from human activities, such as the deliberate firing of forest + grassland in order to clear land for cultivation or improve the quality of grazing

Question 21

explain the combustion of fossil fuels occurring (stats)

Answer 21

• oil, coal + natural gas power the global economy
• currently, the burning of fossil fuels transfers nearly 10GT of CO2/year from geological store to the atmosphere, oceans + biosphere

Question 22

what is carbon sequestration

Answer 22

a natural or artificial process by which carbon dioxide is removed from the atmosphere + held in solid or liquid form

Question 23

explain the role of the physical pump of carbon dioxide in ocean-atmosphere interactions (carbon sequestration)

Answer 23

• CO2 enters the oceans from the atmosphere by diffusion.
• the physical carbon pump involves the mixing of surface + deep ocean waters by vertical currents creating even more distribution of carbon in oceans
• the surface currents then transport this dissolved CO2 polewards where the water cools, becomes more dense + sinks
• this downwelling takes the dissolved carbon to the ocean depths where individual carbon molecules may remain for centuries
• eventually, deep ocean currents transport the carbon to areas of upwelling + the CO2 is brought to the surface + diffuses back into the atmosphere

Question 24

what is upwelling

Answer 24

Upwelling is a process in which deep, cold water rises toward the surface

Question 25

what is downwelling

Answer 25

Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air

Question 26

explain the role of the biological pump of carbon dioxide in ocean-atmosphere interactions (carbon sequestration)

Answer 26

• this is carbon exchanged between oceans + the atmosphere by marine organisms
• phytoplankton drive this biological pump by absorbing carbon as CO2 + combining it with sunlight + water to produce organic material
• the carbon locked in these phytoplankton is released into the oceans as CO2 once the phytoplankton die or after they are consumed in the food chain
• most carbon-rich ocean material ends up into ocean sediments is then lithified to form chalk + limestone

Question 27

what is lithification

Answer 27

Lithification is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock

Question 28

what is vegetation’s role in carbon sequestration

Answer 28

• land plants, especially trees in the rainforests, contain huge stores of carbon
• most of this carbon has been extracted from atmospheric CO2 through photosynthesis + is now locked away for decades

Question 29

how does farming (human activity) affect the carbon cycle

Answer 29

• clearance of forest for farming reduces carbon storage in both above + below ground biomass
• soil carbon storage is reduced by ploughing + exposure of soil organic matter to oxidation
• significant soil erosion occurs during the arable farming process
• often the NPP of crops can exceed the NPP of the previous grassland
• however, photosynthesis generally falls, fundamentally down to the lack of biodiversity

Question 30

what is arable farming

Answer 30

An arable farmer is a farmer who grows ‘cereal crops’

Question 31

how much of global energy consumption have fossil fuels accounted for + how much CO2 is released into the atmosphere annually

Answer 31

fossil fuels account for 87% of global energy consumption, releasing 10 billion tonnes of CO2 into the atmosphere annually

Question 32

what is carbon capture and storage and how does it work

Answer 32

CCS or carbon capture and storage is capture/storage of CO2 released by power plants + industry

• firstly, the CO2 is separated from the power station emissions
• then, CO2 is compressed + transported by pipeline to storage areas
• finally, CO2 is injected into porous rocks deep underground

Question 33

what economic/geographical factors limit carbon capture and storage’s (CCS) effectiveness

Answer 33

• Big capital costs
• Uses large amounts of energy - typically 20% of a power plant’s output is needed to separate + compress CO2
• requires storage reservoirs w specific geological conditions (porous rock overlain by impermeable strata)

Question 34

what state of equilibrium is the global carbon cycle in currently and why

Answer 34

the global carbon cycle is currently in a state of disequilibrium:
- the concentration of CO2 in the atmosphere, the acidity of oceans + the flux of carbon between the major stores have all been distorted by human activity (primarily burning of fossil fuels)

Question 35

what is the carbon fertilisation effect (CFE) and is there evidence for this theory

Answer 35

• the larger the amount of carbon dioxide in the atmosphere that has resulted from rising anthropogenic emissions should help the growth of plants, which use carbon dioxide during photosynthesis
• Despite the correlation between the increase in primary production + the increase in atmospheric CO2, there is yet to be enough evidence to support this theory

Question 36

what is NPP

Answer 36

Net primary productivity (NPP) is defined as the net flux of carbon from the atmosphere into green plants per unit time - the amount of carbon uptake after subtracting ‘plant repiration’ from GPP

Question 37

what is GPP

Answer 37

the total rate at which the ecosystem captures + stores carbon as plant biomass per unit time