6.1 - The carbon cycle and planetary health

Question 1

What is the carbon cycle?

Answer 1

The biogeochemical cycle by which carbon moves from one store to another. It acts as a closed system made up of linked subsystems of sources and sinks

Question 2

What are the main carbon stores?

Answer 2

Terrestrial (lithosphere and biosphere)
Atmospheric
Oceans (hydrosphere)

Question 3

When is the carbon cycle balanced?

Answer 3

It is in equilibrium when the sources equal the sinks.

Question 4

What does anthropogenic mean?

Answer 4

environmental change caused by humans

Question 5

What are the units used to measure stores of carbon?

Answer 5

Petagrams (Pg) or Gigatonnes (Gt) which are both equivalent to 1 billion tonnes

Question 6

What are the 2 main components of the carbon cycle?

Answer 6

Slow moving geological carbon cycle (carbon stores in rocks and sediment)

Fast moving biological carbon cycle (carbon stores in vegetation, soils and the atmosphere)

Question 7

What are the long term and short term carbon stores?

Answer 7

Long term = crustal/terrestrial/geological and oceanic (deep)

Short term = terrestrial soil and ecosystems, oceanic (shallow), atmospheric

Question 8

Where is most of Earth’s carbon?

Answer 8

In geological stores, resulting from the formation of sedimentary carbonate rocks in the ocean and biologically derived carbon in shale, coal and other rocks

Question 9

How is carbon stored in limestone and shale?

Answer 9

Shell building/calcifying organisms and plankton are precipitated onto ocean floor, form layers and are cemented and lithified to form limestone.
Organic compounds from organisms embedded in layers of rock - forming sedimentary rock (shale)

Question 10

How is carbon stored in fossil fuels?

Answer 10

Dead organisms (carbon fixation) sink to bottom of rivers and seas and are covered in silt - decay anaerobically. Heat and pressure exerted on deposits causing fossil fuels to form

Question 11

What happens in chemical weathering of the geological carbon?

Answer 11

Water reacts with atmospheric CO2 to form carbonic acid, which falls as acidic rain and dissolves silicate rocks and releases them into ions. Dissolved into rivers/oceans where they form calcium carbonate and after deposition and burial are turned into limestone

Question 12

What happens in volcanic outgassing, where does it occur?

Answer 12

Volcanoes releasing gas pockets of CO2 to the atmosphere
Occurs at: active/passive volcanic zones associated with tectonic plate boundaries (subduction zones, ridges), places with no current volcanic activity (e.g. Yellowstone), direct emissions from fractures in Earth’s crust

Question 13

How is the geological carbon cycle regulated?

Answer 13

Via negative feedback - takes a few hundred thousand years to rebalance

Question 14

What is carbon sequestration

Answer 14

transfer of carbon from atmosphere -> other stores

-e.g. plant sequesters carbon when it photosynthesises and stores the carbon in its mass

Question 15

What is a carbon cycle pump, what are the 3 key pumps?

Answer 15

Processes operating in oceans to circulate and store carbon.
Biological, carbonate and physical

Question 16

What is thermohaline circulation?

Answer 16

ocean current that produces both vertical and horizontal circulation of cold and warm water around the world’s oceans

-> atmospheric circulation -> large currents in the oceans -> transfers water from warmer tropical areas -> colder polar regions.

-rate of circulation = slow

Question 17

What is the biological pump?

Answer 17

Where phytoplankton (micro organisms) photosynthesise -> take in carbon & turn it into organic matter, they are the base of marine food web -> when they get eaten -> carbon’s passed up the food chain -> & released when these orgainisms respire

-when they decompose -> shells dissolve - carbon becomes part of deep ocean currents -> limestone sediments

or
-co2 reacts with water -> carbonic acid -> then back to atmosphere

Question 18

What is the carbonate pump?

Answer 18

Inorganic carbon sedimentation - marine organisms utilise CaCO3 in their outer shells and inner skeletons. When they die many shells dissolve before reaching sea floor sediments (become part of deep ocean currents), shells that do not dissolve build up on sea floor to form limestone

Question 19

What is the physical pump?

Answer 19

oceanic circulation of water (thermohaline circulation) provides constant source of new water on surface -> transfers surface water into deep ocean -> enables ocean to store so much carbon

Colder water = more potential for CO2 to be absorbed

Warm tropical waters release CO2 to the atmosphere, whereas colder high latitude oceans take in CO2 from the atmosphere

-hence why polar regions hold more carbon than tropical regions

Question 20

What are the 5 distinct phases of thermohaline circulation?

Answer 20

main current begins in polar oceans where water is v cold -> surrounding seawater sinks -> ^ density

current recharged as it passes Antarctica by extra cold, salty, dense water

division of main current: north into Indian Ocean and into Western Pacific

branches warm and rise as they travel northwards, then loop back southward and westward

now warmed waters continue circulating around the globe. On return to north Atlantic they cool and cycle restarts

Question 21

What happens in terrestrial sequestration

Answer 21

Primary producers take carbon out of atmosphere via photosynthesis & release some back via respiration

When consumers eat plants, carbon -> converted into fats, proteins

Microorganisms feed on waste material from animals and carbon becomes part of them - released via respiration.

Question 22

What is marine snow?

Answer 22

A shower of organic material (defecation and dead organic matter) falling from upper waters to the deep ocean

Question 23

Explain how soil is a store of carbon

Answer 23

loss by a plant -> ground transfers carbon to soil

soil microbes break down plants & release carbon -> atmosphere

After organisms die, thousands of compounds in soil are
decomposed.

Question 24

What is the capacity of soil to store organic carbon determined by?

Answer 24

CLIMATE - dictates plant growth and microbial/detritivore activity - rapid decomposition at higher temperatures

SOIL TYPE - clay rich soils have a higher carbon content than sandy soils

MANAGEMENT AND USE OF SOILS - cultivation and disturbance due to land use changes impact how much carbon can be held

Question 25

Why is it important to have a balanced carbon cycle?

Answer 25

Plays a key role in regulating the Earth’s global temperature and climate by controlling the amount of CO2 in the atmosphere, which then affects to hydrological cycle.
Ecosystem development and agriculture depend on the carbon cycle

Question 26

What is the greenhouse effect? *

Answer 26

Earth’s natural temperature control system that relies on greenhouse gases

-31% -> carbon reflected by clouds
-remaining 69% -> absorbed

(greenhouse gases) - co2, methane

Question 27

How has CO2 volume changed in recent years?

Answer 27

CO2 has increased in volume by 40% in the past 300 years

Question 28

What does the natural greenhouse effect influence?

Answer 28

Greenhouse gas increases raise temperature, which in turn affects precipitation patterns

Question 29

What is the importance of photosynthetic organisms?

Answer 29

They help to keep CO2 levels relatively constant, therefore regulating the composition of the atmosphere

Question 30

What is soil health dependent on?

Answer 30

The amount of organic carbon stored in the soil - which is in turn dependent on inputs (plant and animal residues and nutrients) and outputs (decomposition, erosion, use in productivity)

Question 31

Why is carbon in top soil and normal soil important, what effect does soil erosion have on this?

Answer 31

Carbon is ‘active’ in topsoil, whereas in soil organic matter it gives soil it’s water retention capacity, it’s structure and fertility
Organic carbon is concentrated in the surface soil layer as easily eroded small particles, so soil erosion is a major threat to carbon storage and soil health

Question 32

How has fossil fuel combustion changed in recent decades?

Answer 32

Fossil fuels have been burnt at increasing rates since the start of the Industrial Revolution, as they continue to be the primary energy source driving modern civilization

Question 33

How has fossil fuel combustion altered the balance of carbon pathways and stores?

Answer 33

half of extra emissions have remained in the atmosphere
the rest has been fluxed from the atmosphere into the stores of the oceans, ecosystems and soils
IMPACTS - increased fluxes to the biological store, increased soil storage in high latitudes, loss of storage in unfreezing permafrost/oceans due to warming

Question 34

What are the implications of fossil fuel combustion for the climate?

Answer 34

Globally - Earth will become warmer, thermohaline current affected by slowing/reversal of the Gulf Stream, rising mean sea level, more extreme, intense and frequent events
Regionally - some regions warmer, others wetter, storm surges may increase

Question 35

What are the implications of fossil fuel combustion for ecosystems?

Answer 35

-rising sea level -> as ice sheets, glaciers are melting- impacts coastal species

-ecosystems -> change in distrbution of species, marine organisms threatened by lower o2 lvels, ocean acidification

Question 36

What are the implications of fossil fuel combustion for the hydrological cycle?

Answer 36

increase evaporation rates, and therefore moisture circulation through the cycle

change precipitation type

reduce sea ice, ice cap and glacier storage
change capacity of terrestrial ecosystems to sequester carbon and store water
droughts and floods driven by ENSO become more intense and increase in frequency

Question 37

What are the 3 forms of carbon in the carbon cycle

Answer 37

-inorganic - found in rocks as bicarbonates, carbonates

-organic - found in plant material, living organisms

-gaseous - found as co2, ch2

Question 38

what are fluxes

Answer 38

movement/ transfer of carbon between stores

Question 39

What is a carbon sink

Answer 39

any store which takes in more carbon than it emits

-e.g. tropical rainforest

Question 40

What is a carbon source

Answer 40

any store that emits more carbon than it stores

-e.g. damaged tropical rainforest

Question 41

Name the 4 types of stores that carbon is present in

Answer 41

The atmosphere as CO2 and methane

The hydrosphere as dissolved CO2

The lithosphere as carbonates in limestone and fossil fuels like coal, gas and oil

The biosphere in living and dead organisms

Question 42

Name the 6 main carbon stores

Answer 42

-marine sediments, sedimentary rocks - lithosphere - long-term -> biggest store recycle rock

-oceans - hydrosphere - dynamic -> 2nd biggest -> carbon constantly utilised by marine organisms

-fossil fuel deposits - lithosphere -> long-term, currently dynamic -> humans have developed tech to exploit rapidly

-soil organic matter - lithosphere -> mid term- soil stores carbon - deforestation, agriculture, land use changes X impact

-atmosphere - dynamic -> since industrial rev - co2 in atmosphere ^ by 40%

-terrestrial plants - biosphere - mid-term -> carbon storage in forests = decreasing -> climate change, deforestation

Question 43

Name the 6 fluxes within the carbon cycle

Answer 43

-photosynthesis

-respiration

-combustion

-decomposition

-diffusion

-sedimentation

-weathering and erosion

-metamorphosis

-volcanic outgassing

Question 44

Explain how photosynthesis is a flux within the carbon cycle

Answer 44

Living organisms convert CO2 from the atmosphere and water from the soil -> O2 and Glucose using Light Energy.

By removing CO₂ from the atmosphere, plants are sequestering carbon and reducing the potential impacts of climate change. The process of photosynthesis occurs when chlorophyll in the leaves of the plant react with CO₂, to create the carbohydrate glucose.

Photosynthesis helps to maintain the balance between oxygen and CO ₂ in the atmosphere.

The formula is shown below:
Carbon Dioxide + Water → Light Energy → Oxygen + Glucose

-> overall absorb more carbon than they emit so they are net co2 absorbers, net o2 producers

Question 45

Explain how respiration is a flux within the hydrological cycle

Answer 45

Respiration occurs when plants and animals convert oxygen and glucose
into energy which then produces the waste products of water and CO ₂.

opposite of photosynthesis:
Oxygen + Glucose → Carbon Dioxide + Water

Question 46

Explain how combustion is a flux

Answer 46

When fossil fuels and organic matter such as trees are burnt, they emit CO ₂
into the atmosphere.

may occur when fossil fuels are burnt to produce energy, or if wildfires occur.

Question 47

Explain how decomposition is a flux

Answer 47

When living organisms die -> broken down by decomposers which respire, returning CO₂ into the atmosphere.

Some organic matter is also returned to the soil where it is stored adding carbon matter to the soil.

Question 48

Explain how diffusion is a flux

Answer 48

The oceans can absorb CO ₂ from the atmosphere -> this has ^
ocean acidity by 30%

The ocean is the biggest carbon store,
but with carbon levels increasing seawater becomes more acidic which is harming aquatic life by causing coral bleaching. Many of the world’s coral reefs now under threat.

Question 49

Explain how sedimentation is a flux

Answer 49

This can happen on land or in the sea. For example, when shelled marine
organisms die, their shell fragments fall to the ocean floor and become compacted over time to form limestone. Organic matter from vegetation and decaying marine organisms is compacted over time, whether on land or in the sea, to form fossil fuel
deposits.

Question 50

Explain how weathering and erosion is a flux

Answer 50

Inorganic carbon is released slowly through weathering: rocks
are eroded on land or broken down by carbonation weathering. Carbonation weathering occurs when CO ₂ in the air mixes with rainwater to create carbonic acid which aids erosion of rocks such as limestone . The carbon is moved through the water cycle and
enters the oceans. Marine organisms use the carbon in the water to build their shells .
Increasing carbon dioxide levels in the atmosphere, may increase weathering and erosion
as a result, potentially affecting other parts of the carbon cycle

Question 51

Explain how metamorphosis is a flux

Answer 51

– Extreme heat and pressure forms metamorphic rock, during which some
carbon is released and some becomes trapped.

Question 52

Explain how volcanic outgassing is a flux

Answer 52

There are pockets of CO2
found in the Earth’s crust. During a
volcanic eruption or from a fissure in the Earth’s crust, this CO2 can be released

Question 53

variations in the carbon cycle

Question 54

Give a brief description of the thermohaline circulation process

Answer 54

Water in North Atlantic is cold, very saline -> denser and heavier -> sinks

when cold water sinks, warm water is drawn from the ocean surface

Eventually cold water is drawn from the bottom of the ocean and then warmed up.

Question 55

Why is the thermohaline circulation important in terms of regulating climate, minimising climate change

Answer 55

-as colder the water, the more CO2 is absorbed

-so if ocean temps ^ -> oceans absorb less co2 -> accelerating climate change -> more ocean warming

Question 56

Name the 2 ways carbon fluxes due to terrestrial

Answer 56

Diurnally – during the day, fluxes are positive from the atmosphere to the ecosystem
where as in the night, fluxes are negative from the atmosphere to the ecosystem.

Seasonally – In the northern hemisphere during winter, plants die and decay leading
to high atmospheric CO2
concentrations but during spring when plants begin to grow,
CO2 levels in the atmosphere begin to drop.

Question 57

What is required to maintain stable average temperatures

Answer 57

constant levels of co2

Question 58

What does the enhanced greenhouse effect mean and why is it bad

Answer 58

human activities (fossil fuels, coal, oil) generate ^ greenhouse gases

-these gases trap more heat ^ earth’s surface temperature

Question 59

Name 6 human activites which has led to more carbon being released into atmosphere and less carbon being absorbed

Answer 59

-land use change -> release more carbon & impact short-term carbon stores - atmosphere, soil

e.g.

-farming pratices -> deforestation for cattle -> cattle produce large amounts of methane -> ^ GW

-fertilisers -> emit greenhouse gases -> ^ GW

-deforestation -> reduces carbon sequestration -> land becomes carbon source not carbon sink

-urbanisation -> affects local, global carbon cycle -> vegetation replaced, soil covered by cement -> releases co2 during production

-combustion of fossil fuels -> co2 released into atmosphere

Question 60

Name the 5 implications of the enhanced greenhouse effect

Answer 60

-temperature ->

-climate ->

-precipitation ->

-ecosystems ->

-hydrological cycle ->

Question 61

pg. 88-93

Question 62

How do the 3 carbon cycle pumps interlink

Answer 62

-biological -> phytoplankton (marine plants) float near ocean surface -> access to sun -> photosynthesis -> fish eat them -> carbon passed on -> released as co2 back into water, atmosphere, some carbon reaches seafloor when phytoplankton die

-carbonate -> marine organisms use calcium carbonate to make harder outer shells -> carbon becomes part of deep ocean currents -> accumilates -> limestone

-physical -> oceanic circulation of the water -> cold water absorbs co2 from atmosphere, warm water releases co2 -> atmosphere

-pumps altogether flux surface ocean co2 -> deep ocean