Carbon EQ1 - 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

Processes and actions associated with human activity

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

What are the key processes in the geological carbon cycle?

Answer 9

• mechanical, chemical and biological weathering
• decomposition
• transportation
• sedimentation
• metamorphosis

Question 10

How is carbon stored in limestone and shale?

Answer 10

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 11

How is carbon stored in fossil fuels?

Answer 11

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 12

What are the 2 main geological processes moving carbon?

Answer 12

• chemical weathering of silicate rock
• volcanic outgassing at ocean ridges and subduction zones

Question 13

What happens in chemical weathering of the geological carbon?

Answer 13

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 14

What happens in volcanic outgassing, where does it occur?

Answer 14

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 15

How is the geological carbon cycle regulated?

Answer 15

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

Question 16

What is sequestrating?

Answer 16

The natural storage of carbon by physical or biological processes such as photosynthesis

Question 17

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

Answer 17

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

Question 18

What is thermohaline circulation?

Answer 18

The global system of surface and deep water ocean currents driven by temperature and salinity differences between areas of the ocean

Question 19

What is the biological pump?

Answer 19

The organic sequestration of CO2 to oceans by phytoplankton. Phytoplankton have high NPP and are the base of the marine food web, carbon is then passed up the food chain, releasing CO2 back into the water and atmosphere (respiration). Some decompose and reach ocean floor

Question 20

What is the carbonate pump?

Answer 20

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 21

What is the physical pump?

Answer 21

Based on oceanic circulation of water (thermohaline circulation). 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. CO2 accumulated at surface taken down with cooler water.

Question 22

What are the 5 distinct phases of thermohaline circulation?

Answer 22

1. main current begins in polar oceans where water is cold, sea ice forms, water gets saltier, increases in density and sinks
2. current recharged as it passes Antarctica by extra cold, salty, dense water
3. division of main current: north into Indian Ocean and into Western Pacific
4. branches warm and rise as they travel northwards, then loop back southward and westward
5. now warmed waters continue circulating around the globe. On return to north Atlantic they cool and cycle restarts

Question 23

What is the time scale of ocean sequestration?

Answer 23

CO2 gas exchange flux between oceans and atmosphere operates on timescale of several hundred years

Question 24

What is the time scale of terrestrial sequestration?

Answer 24

Shortest time scale - only seconds, minutes or years

Question 25

What happens in terrestrial carbon cycle?

Answer 25

Primary producers take CO2 out of atmosphere via photosynthesis (terrestrial sequestration) and release some back via respiration. When consumers eat plants, carbon becomes part of biomass. Microorganisms and detritus feeders feed on waste material from animals and carbon becomes part of them - released via respiration.

Question 26

What is the role of phytoplankton in the ocean food web and carbon cycle?

Answer 26

Form the base of the aquatic food web (primary producers)
Carbon cycle - consumer CO2 on a scale equivalent to forests, part of biological carbon pump

Question 27

What is marine snow?

Answer 27

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

Question 28

How do terrestrial carbon fluxes vary?

Answer 28

• diurnally (during day = positive flux, at night = negative flux)
• seasonally (winter = more CO2, spring = less CO2 as plants begin to grow again)

Question 29

What happens to biological carbon?

Answer 29

Either stored in dead organic matter in soil, or returned to atmosphere via biological decomposition

Question 30

What are the 2 sources of carbon in soils?

Answer 30

• arid and semi arid soils contain inorganic carbon
• organic carbon from plant photosynthesis and subsequent decomposition

Question 31

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

Answer 31

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

Question 32

How is the carbon balance in soils regulated?

Answer 32

Plant productivity, microbial activity, geology, erosion, climate and the amount of upward and downward (leaching) water movement in the soil

Question 33

Why is it important to have a balanced carbon cycle?

Answer 33

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 34

What is the greenhouse effect?

Answer 34

Earth’s natural temperature control system that relies on greenhouse gases
Driven by incoming shortwave solar radiation, about 70% of which is absorbed - and of this, 70% is then re-radiated to space as longwave radiation. However, a large proportion of the longwave radiation is re-radiated to the surface again by greenhouse gases

Question 35

How has CO2 volume changed in recent years?

Answer 35

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

Question 36

What does the natural greenhouse effect influence?

Answer 36

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

Question 37

What is the importance of photosynthetic organisms?

Answer 37

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

Question 38

Where are the areas of highest NPP on land and in the oceans?

Answer 38

On land - in areas that are warm and wet (carbon storage is also high in areas that have permafrost such as tundra)
In the oceans - in shallower waters, allowing higher photosynthesis and in places receiving high nutrient inputs

Question 39

What is soil health dependent on?

Answer 39

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 40

What are the three main carbon/nutrient stores in soils?

Answer 40

Biomass
Litter
Soil

Question 41

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

Answer 41

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 42

How has fossil fuel combustion changed in recent decades?

Answer 42

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 43

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

Answer 43

• 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 44

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

Answer 44

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 45

What are the implications of fossil fuel combustion for ecosystems?

Answer 45

Biomes most at risk = Arctic and coral ecosystems. Direct influence on changing services of ecosystems and biodiversity. Coastal ecosystems will be under risk for centuries.
Some positives = cool moist regions like UK could provide habitats for additional species

Question 46

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

Answer 46

• 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