The carbon cycle

Question 1

What type of system is the carbon cycle?

Answer 1

A closed system - when energy inputs equal outputs, doesn’t allow transfer of matter in or out of the system

Question 2

How does photosynthesis affect the transfer of carbon between stores?

Answer 2

• Living organisms convert CO2 from the atmosphere and water from the soil, into oxygen and glucose using light energy.
• By removing CO2 from the atmosphere, plants are sequestering carbon and reducing the amount of carbon.
• Photosynthesis occurs when chlorphyll in the leaves of the plant react with CO2 to create the carbohydrate glucose, this helps to maintain the balance between CO2 and oxygen in the atmosphere.

(Fast cycle)

Question 3

What is the fast carbon cycle?

Answer 3

• Transfer of carbon in and out of the biosphere and atmosphere
• Takes up to 100,000 million tonnes of carbon through the biosphere every year and happens relatively quickly (over months and years), varying seasonally

Question 4

What are four ways carbon can return to the atmosphere? (fast cycle)

Answer 4

1. Plants respire to grow and release carbon
2. Plants are consumed by other organisms, which respire and release carbon
3. Plants die and decompose
4. Plants are combusted

Question 5

What is the slow carbon cycle?

Answer 5

• Refers primarily to the transfer of carbon between the atmosphere, hydrosphere and lithosphere
• Weathering and erosion of rocks adds carbon to the ocean either directly (in coastal environments) or indirectly (via rivers)
• Sediment accumulates on the ocean floor, creating new sediment layers, this sediment enters the lithosphere forming new crust in the form of rock
• Tectonic forces recycle this sediment back into the atmosphere, at plate boundaries through volcanies eruptions, and underwater and ground vents
• It moves 10 to 100mill tonnes every year but it takes 100 and 200 million years for carbon to move through this cycle

Question 6

What chemical feedbacks regulate this? (slow cycle)

Answer 6

• Increase in atmospheric carbon dioxide raises global temperature, leading to more rain and dissolving more rock
• Over hundreds of thousands of years the slow carbon cycle rebalances after a disturbance
• The slow carbon cycle has been important over geological time, but has limited impact on the current climate changes we have seen over a few centuries

Question 7

How does respiration affect the transfer of carbon between stores?

Answer 7

• Respiration occurs when plants and animals convert oxygen and glucose into energy which then produces the waste products of water and CO2 (therefore chemically the opposite of photosynthesis)
  oxygen + glucose –> carbon dioxide + water
• During the day plants photosynthesise, absorbing more CO2 than they emit from respiration, during the night they don’t photosynthesise, they respire releasing more CO2 than they absorb
• Overall plants absorb more CO2 than they emit, so are net carbon dioxide absorbers (from the atmosphere) and not oxygen producers (to the atmosphere)
• (fast carbon cycle), moving glucose from biosphere store to atmospheric store in the form of CO2

Question 8

How does decomposition affect the transfer of carbon between stores?

Answer 8

• Living organisms which have died are broken down by decomposers (bacteria and detrivores) which respire, returning CO2 into the atmosphere
• Some organic matter is also returned to the soil where it is stored adding carbon to the soil
• (slow carbon cycle), carbon from dead matter in the biosphere is moved to the atmosphere in the form of CO2

Question 9

How does combustion affect the transfer of carbon between stores?

Answer 9

• Fossil fuels or organic material which contains carbon, are burned in the presence of oxygen it is converted into energy, CO2 and H2O
• Releasing carbon that may have been stored in rocks for millions of years
• Fires can also burn slowly underground for many years in peat deposits (areas of land where partially decomposed organic matter has accumulated over thousands of years to form a type of soil called peat) releasing long-stored carbon into the atmosphere
• (fast carbon cycle), lithosphere and biosphere to lithosphere

Question 10

How does burial and compaction affect the transfer of carbon between stores?

Answer 10

• Shelled organisms take up CO2 from H2O and convert it to ccalcium carbonate, used to build their shells
• When shelled marine organisms die, after millions of years hydrocarbons are formed (oil and coal)
• Some of these carbonates dissolve, releasing CO2 and the rest becomes compacted to form limestone, storing carbon for years
• (slow carbon cycle), biosphere to lithosphere to hydrosphere/atmosphere

Question 11

How does carbon sequestration affect the transfer of carbon between stores?

Answer 11

• Transfer of carbon from the atmosphere to other stores can be natural and artificial
• A plant sequesters carbon when it photosynthesises and factories are also starting to use carbon capture and storage, captured and transported via pipeline to depleted gas field (places where natural gas has been extracted) and saline aquifers (underground rock formations containing salty water), trapping CO2 and keeping it safely stored for long periods of time

Question 12

How does weathering and erosion affect the transfer of carbon between stores?

Answer 12

• Rocks are eroded on land or broken down by carbonation weathering
• Carbonation weathering occurs when CO2 in the air mixes with rainwater to create carbonic acid which aids erosion of rocks such as limestone
• This carbon is moved through the water cycle and enters oceans
• Marine organisms use the carbon in the water to build their shells, increasing CO2 in the atmosphere may increase weathering

Question 13

What is a carbon sink?

Answer 13

Stores that absorb more carbon than it releases

Question 14

What is a carbon source?

Answer 14

Releases more carbon than it absorbs

Question 15

What is the total carbon and how much is stores in each

Answer 15

Total carbon = 142310 gigatonnes
Lithosphere = 70%
Crysophere, biosphere and atmosphere = 1%
Hydrosphere = 27%

Question 16

How is carbon stored in the litosphere?

Answer 16

• Stored in sedimentary rocks with the planet’s crust, (rocks produced by the hardening of mud into shale over geological time)
• All sedimentary rocks on Earth store 100,000,000 pq
• 4,000 pq is stored in the Earth’s crust as hydrocarbons formed over millions of years from ancient living organisms under intense temperature and pressure (fossil fuels)

Question 17

How is carbon stored in the hydrosphere?

Answer 17

• Contains 38,000 pq - mostly in the form of dissolved inorganic (oxidised) carbon
• 1000pq is located near the ocean surface, this is exchanged rapidly with the atmosphere through both physical processes, CO2 dissolving into water, and biological processes, growth death and decay of plankton
• Most surface carbon cycle rapidly, some can be transfered by sinking to the deep ocean pool where it can be stored for longer

Question 18

How is carbon stored in the atmosphere?

Answer 18

• Contains 750 pq, mostly in the form of CO2 with other compounds
• Small size of the atmospheric carbon pool makes it more sensitive to disruptions caused by an increase in sources or sinks of carbon from the Earth’s other pools
• Present day value, is substantially higher than that which occurred before the onset of fossil fuel combustion and deforestation - 560 pq

Question 19

How is carbon stored in the biosphere? (terrestrial ecosystems)

Answer 19

• 560pq stored
• Woody stems have the greatest ability to store large amounts of carbon
• Plants exchange carbon with the atmosphere rapidly through photosynthesis

Question 20

How is carbon stored in the pedosphere?

Answer 20

• Contains 1500pq
• As soil depth increases, abundance of organic carbon decreases

Question 21

How is carbon stored in the crysophere?

Answer 21

• Stores 1500pq
• Permafrost locks in organic matter in the frozen soil, storing carbon
• Rising temperatures melt permafrost releasing carbon into the atmosphere

Question 22

What are the different seres?

Answer 22

Hydrosere = fresh water ecosystem
Lithosere = rock ecosystem
Psammosere = sand ecosystem
Holosere = salt water ecosystem

Question 23

What is vegetation succession?

Answer 23

Development of an ecosystem.

Question 24

What is the seral stage?

Answer 24

A stage in the devlopment of an ecosystem.

Question 25

What is a climax community?

Answer 25

The final seral stage in the succession without human interference, e.g. UK temperate deciduous forest, in a stage of dynamic equilibrium.

Question 26

What is a plagioclimax community?

Answer 26

The ecosystem which exists alongisde human activity.

Question 27

What is a pioneer species?

Answer 27

The first species to colonise land in each seral stage.

Question 28

What is primary succession?

Answer 28

The development of an ecosystem for the first time in a particular place.

Question 29

What is secondary succession?

Answer 29

The redevelopment of an ecosystem after severe interference.

Question 30

How are fossil fuels formed?

Answer 30

1. Organic matter accumulation
   - Their remains accumulate usually in swampy or marine environments where oxygen levels are low - this helps prevent complete decomposition
2. Burial and pressure
   - Layers of sediment accumulate on top of the organic matter - the weight of these layers exert pressure on the organic material below, leading to increased temperature and pressure conditions
3. Chemical transformation
   - As temperature and pressure increase, the organic matter undergoes chemical changes - for plant matter this leads to the formation of coal
   - For marine organisms it can lead to formation of oil + natural gas
4. Migration
   - Oil and gas can migrate through porous rock layers until they are trapped by non-porous rocks

Question 31

How are forest areas changing?

Answer 31

• Brazil has the most carbon stored on land and the most extensive deforested area
• China has the largest amount of afforested area

Question 32

How does the carbon cycle vary due to physical changes? (wildfires)

Answer 32

• Can be started naturally however they are increasingly started by humans
• Indonesia suffers from recurring wildfires every year as areas of land are cleared to make way for commercial agriculture, settlement or infrastructure
• In 2019, an El Nino event caused a prolonged dry spell and strong winds fanned the flames, the fires blanketed Indonesia and the region with haze
• Caused 900,000 people to suffer from respiratory illness and cost the US 5.2bn
• In 2015, an air pollution crisis affected more than 28mil people in the region

Question 33

How does the carbon cycle vary due to physical changes? (volcanic activity)

Answer 33

• During the Palaeozaic era volcanoes were much more active than they are today, a vast amount of carbon dioxide was emitted into the atmosphere, where it remained
• Volcanoes emit between 130 and 380 million tonnes of CO2 per year - humans emit about 30 billion tonnes of CO2 per year
• Volcanoes also erupt lava, which contains silicataes that will slowly weather - converts CO2 in the air to carbonates in solution, CO2 is absorbed very slowly from the atmosphere

Question 34

How does the carbon cycle vary physically? (natural climate change)

Answer 34

• Vostok ice core data from Antarctica suggests that the temperature change has occurred before carbon dioxide levels have risen
• Variations in the Earth’s orbit (eliptical or oval) cause periods of time where we altering the amount of energy recived from the Sun, leading to a cycle of ice ages and warm periods
• Increase in temperatures, causes glaciers to melt and therefore increases flows in carbon cycle, allowing more CO2 to enter the atmosphere and for global temps to rise further (positive feedback)
• Cooler temperatures and increased phytoplankton growth may have increased the amount of carbon the ocean took out of the atmosphere (negative feedback)

Question 35

Examples of positive feedback in the carbon cycle

Answer 35

• Wildfires are more likely in hotter and drier climated, releasing large quantities into the atmosphere, increasing the warming effect
• Ice reflects radiation from the sun, reducing surface warming - as sea temperatures rise and ice melts, the warming is amplified as there is less ice to reflect the radiation, further melting occurs

Question 36

Example of neagtive feedback in the carbon cycle.

Answer 36

• Increased photosynthesis by plants and rising global temps allows vegetation to grow in new areas, e.g. where permafrost has melted - new vegetation absorbs CO2, decreasing the warming effect

Question 37

How does the carbon cycle change due to humans? (combustion of fossil fuels)

Answer 37

• According to the Intergovernmental panel on climate change about 90% of human related carbon release comes from fossil fuel combustion
• Roughly 1/2 of the anthropogenic carbon is absorbed equally by oceand and vegetation and the remainder is absorbed by the atmos.
• Since the 1960s, global concentration of CO2 has increased from 320ppm to 400ppm
• Finland and the Netherlands had carbon taxes implemented in 1999, UK introduced in 2010
• Taichung Power Plant located in Taiwan, largest coal-fired power plant in the world, 6.6% of Taiwan’s operating reserve

Question 38

How does the carbon cycle change due to humans? (farming)

Answer 38

• Cattle in the USA emit around 5.5 million tonnes of methane per year into the atmosphere, around 20% of the total methane emissions of the USA
• Production of rice may contribute up to 20% of global methane emissions
• Machinery is fuelled by fossil fuels and fertilisers are based on fossil fuels
• Shimpling Park Farm, Suffolk 645 hectares, arable organic farm
• Emits 1150 tonnes of CO2 per year mainly from fuel
• 40% of the CO2 emissions are offset by carbon sequestration
• To decrease CO2, use compost across the grass, increasing its store of carbon as manure released greenhouse gasses
• Silvopasture - the practice of integrating trees, forage, and the grazing of domesticated animals in a mutually beneficial way

Question 39

How does the carbon cycle change due to humans? (deforestation)

Answer 39

• Turns carbon sinks into carbon sources
• When a tree dies, it decomposes slowly and releases carbon over a long time, during this vegetation starts to grow compensating for the carbon being released (carbon neutral)
• Deforestation accounts for 20% of all CO2 emissions globally
• UK, 13% is covered with forests, the European average is 38%, we were at 5% in 1905

Question 40

How does the carbon cycle change due to humans? (urbanisation)

Answer 40

• Urban areas account for 97% of global fossil fuel emissions
• Urbanisation in the tropics is responsible for 5% of annual emissions
• Cement production contributes to 7.4% of global carbon emissions
• 1 tonne of cement = 1 metric tonne of CO2
• “Solidia” - cement company, can cut CO2 emissions by 70% by changing the proportions of limestone and sand 1:1, allowing them to heat it 300C lower at 1,200 - 30% less energy and emits 40% less carbon
• They trap CO2 within the product itself

Question 41

What is the carbon budget?

Answer 41

Uses data to describe the amount of carbon that is stored and transferred within the carbon cycle.

Question 42

What is the greenhouse effect?

Answer 42

Gases absorb long-wave radiation, trapping heat from the sun and warm the lower atmosphere.

Question 43

What are the impacts of the carbon cycle on land, ocean and atmosphere?

Answer 43

Land - Responsible for the development and formation of soil, carbon in the form of organic matter introduces important nutrients and provides a structure to the soil.

Ocean - Carbon can be converted into calcium carbonate, which is used by some marine organisms to build shells.

Atmosphere - Helps to warm the Earth through the greenhouse effect, enabling life on Earth.