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g: wcc > 1.3: The Carbon Cycle > Flashcards

1.3: The Carbon Cycle Flashcards

1
Q

Outline some important examples of carbon compounds.

A
  • CO2
  • methane (CH4)
  • calcium carbonate (CaCO3)
  • hydrocarbons
  • biomolecules (complex carbon compounds produced in living things. Eg carbohydrates, DNA).
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2
Q

What is anthropogenic CO2?

A

CO2 generated by human activity.

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3
Q

What is the primary source of CO2?

A

The Earth’s interior - it was stored in the mantle when the Earth was formed, and escapes from the mantle at constructive and destructive plate boundaries. As well as hotspot volcanoes.

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4
Q

Much of the CO2 is released at destructive plate boundaries. Where is this CO2 derived from?

A

The metamorphism of carbonate rocks subduction with the ocean crust.

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5
Q

In what way can carbon be removed into long term storage?

A

By burial of sedimentary rick layers, especially coal (which stored organic carbon from i decayed biomass). As well as carbonate rocks eg limestone (CaCO3).

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6
Q

What is the lithosphere?

A

The crust and uppermost mantle; constituting the hard and rigid outer layer of the Earth.

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7
Q

What is the biosphere?

A

The total sum of all living matter.

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8
Q

What is the pedosphere?

A

The uppermost part of the lithosphere - the layer that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process.

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9
Q

What are the main stores of carbon in the lithosphere?

A
  • marine sediments & sedimentary rock.
  • peat
  • fossil fuel deposits of coal, oil and gas
  • soil organic matter
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10
Q

How much carbon is stored in the lithosphere as marine sediments and sedimentary rocks?

A

100m GtC.

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11
Q

How much carbon is stored in the lithosphere as soil organic matter?

A

1500 GtC

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12
Q

How much carbon is stored in the lithosphere as fossil fuel deposits of coal, oil and gas?

A

4000 GtC

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13
Q

How much carbon is stored in the lithosphere as peat?

A

250 GtC

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14
Q

What is peat?

A

Dead but undecayed organic matter found in boggy areas.

Forms in wetland conditions where (almost) permanent water saturation obstructs flows of oxygen from the atmosphere into the ground - creating low oxygen anaerobic conditions that slow down the rate of plant litter decomposition.

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15
Q

What are the three oceanic stores of carbon?

A
  • the surface layer (euphotic zone)
  • the intermediate (twilight zone) and deep layer
  • living organic matter
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16
Q

Outline the oceanic store: the surface layer (euphotic zone).

A

Where sunlight penetrates so photosynthesis can take place.

900 GtC.

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17
Q

Outline the oceanic store: the intermediate (twilight zone) and deep layer of water.

A

37,000 GtC.

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18
Q

Outline the oceanic store: organic matter.

A

Living organic matter: 30 GtC.

Dissolved organic matter: 700 GtC.

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19
Q

What is the total amount of oceanic carbon?

A

40,000 GtC.

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20
Q

What is the total amount of carbon stored in the terrestrial biosphere?

A

3000 GtC.

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21
Q

What are the 5 main stores of carbon in the terrestrial biosphere?

A
  • living vegetation
  • plant litter
  • soil humus
  • peat
  • animals
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22
Q

Outline living vegetation as a store of carbon in the terrestrial biosphere

A
  • 19% of carbon in Earth’s biosphere is stored in plants.
  • much is stored directly in tissues of the plant’s (unlike oceans)
  • the amount of carbon in dry biomass varies from 35-65% of dry weight (but depends on location and vegetation type).
  • 1/2 of the carbon in forests occurs in high latitude forests, and 1/3 in low latitude forests
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23
Q

What is plant litter?

A

Fresh, undecomposed and easily recognisable plant debris. Eg leaves, cones, twigs, bark.

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24
Q

Leaf tissue account for ___% of litter in forests.

A

70%

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25
Q

What is soil humus?

A

A thick brown substance that remains after most of the organic litter has decomposed. Dispersed throughout soil by organisms eg earthworms.

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26
Q

How much carbon is found in soil humus?

A

2500 GtC:

Organic (1550 GtC) and inorganic (950 GtC).

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27
Q

How much carbon does peat contain?

A

250 GtC worldwide.

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28
Q

When were atmospheric CO2 levels at their highest?

A

In the Cambrian period (at 7000ppm). Around 500m years ago.

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29
Q

When have CO2 levels been at their lowest?

A

Over the last 2m years during the Quaternary glaciation (when CO2 levels sank to 180ppm).

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30
Q

What are the CO2 levels today in the atmosphere?

A

400ppm (around 800 GtC).

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31
Q

CO2 is a greenhouse gas. What is this?

A

Any gaseous compound in the atmosphere that’s capable of absorbing infrared radiation, thereby trapping and holding heat in the atmosphere.

32
Q

Where is atmospheric carbon measured?

A

The Mauna Loa Observatory (MLO) in Hawaii.

33
Q

Why is atmospheric carbon measured at the Mauna Loa Observatory in Hawaii?

A

Because the air is undisturbed, in a remote location and there are minimal influences of vegetation and human activity.

34
Q

The MLO has observed that the global annual mean conc of CO2 has increased markedly since…

A

The industrial revolution.

Largely due to anthropogenic sources, possible burning of fossil fuels and deforestation.

35
Q

What is a carbon sink?

A

A store of carbon that absorbs more carbon than it releases

36
Q

What is a carbon source?

A

More carbon leaves a store than enters it.

37
Q

What is the geological component of the carbon cycle?

A

Where it interacts with the rock cycle in the processes of weathering, burial, subduction and volcanic eruptions.

38
Q

How is CO2 removed from the atmosphere?

A

By dissolving in water and forming carbonic acid.

(CO2 + H2O -> H2CO3 (carbonic acid)).

39
Q

What happens when creatures eg molluscs die?

A

Their skeletons sink to the bottom of the oceans where they collect as sediment.

Then, burial by overlying sediment can eventually turn these sediments into sedimentary limestone.

40
Q

What relevance does tectonic uplift have to the movement of carbon?

A

Tectonic uplift can expose buried limestone (e.g. dead coral being built upon by later generations of live coral).

41
Q

Give a real life example of tectonic uplift.

A

In the Himalayas, where some of the world’s highest peaks are formed of material that was once at the bottom of the ocean.

42
Q

Once CO2 has been buried in oceans, how can it return to the atmosphere?

A

Tectonic forces cause plate movement to push the sea floor under continental margins in the process of subduction.

The carbonaceous seafloor deposits are pushed deep into the Earth where they heat up, eventually melt and rise back up to the surface through volcanic eruptions or CO2 rich springs.

43
Q

Outline photosynthesis as a movement of carbon?

A

Phytoplankton in the euphotic zone (sunlit surface waters), algae etc use sunlight energy to turn combine CO2 from atmosphere with water into carbohydrates. Oxygen is a byproduct.

44
Q

Outline respiration as a movement of carbon.

A

Plants, (and algae and bacteria) use the stored carbs as an energy source to carry out respiration. Getting their energy from excess biomass (eg bulk of the plant).

o2 + carb -> energy + water + CO2.

45
Q

What is decomposition?

A

Physical, chemical and biological mechanisms that transform organic matter into increasingly stable forms (by physical break up eg wet-dry, hot-cold, shrink-swell cycles etc).

46
Q

What are the chemical transformations of decomposition?

A

Oxidation and condensation.

47
Q

What do the biological mechanisms of decomposition include?

A

Deeding and digestion (aided by enzymes).

48
Q

What does decomposition ensure?

A

That the important elements of life (eg carbon, hydrogen, oxygen, nitrogen etc) can be continuously recycled into the soil and made available for life.

49
Q

Outline oceanic carbon pumps are a movement of carbon.

A
  • there’s a negative correlation between the temp of water and amount of CO2 that can be dissolved. This leads to VERTICAL DEEP MIXING.
  • in this way, vertical circulation ensures that CO2 is being exchanged between the ocean and atmosphere - acting as an enormous carbon pump (and giving the ocean a lot more carbon than if surface water wasn’t being constantly replaced).

• biological pump which locks carbon up for millions of years.

50
Q

Oceanic carbon pumps is a movement of carbon. What is vertical deep mixing within this?

A

Occurs when warm water in oceanic surface currents is carried from the warm tropics to cold polar regions. Here, water is cooled, making it dense enough to sink below the surface layer, sometimes all the way to the ocean floor.
When cold water returns to the surface and warms up again, it loses CO2 to the atmosphere.

This acts as a huge carbon pump.

51
Q

Oceanic carbon pumps are a movement of carbon. And biological pumps are within this, but what are they?

A

Carbon is incorporated into marine organisms as organic matter / CaCO3. When organisms die, their dead cells, shells and other parts sink into deep water. Decay releases CO2 into deep water, and some material inks right to the bottom where it forms layers of carbon rich sediments.

Over millions of years, chemical and physical processes may turn these sediments into rocks, and lock up carbon for millions of years.

52
Q

Outline combustion as a movement of carbon.

A

Occurs when organic material is reacted (burned) in the presence of oxygen to give off CO2, water and energy.

If certain elements are present, they do,nine with oxygen to form a variety of pollutant molecules eg nitrogen oxides.

53
Q

What is biomass combustion?

A

The burning of living and dead vegetation. Including natural and human induced burning.

54
Q

Volcanic activity is a movement of carbon. But why has is “never caused detectable global warming of the atmosphere”?

A
  • the warming effect of emitted CO2 is counterbalanced by the large amount of sulphur dioxide given out. (Conversion of this sulphur dioxide to sulphuric acid, which forms fine droplets, increases the reflection of radiation from the sun, back into space - cooling Earth’s atmosphere).
  • the amounts of CO2 released haven’t been enough to produce detectable global warming. Eg all studies to date of global volcanic CO2 emissions indicate that present day sub-aerial and submarine volcanoes have released less than 1% of the CO2 released by currently by human activities.
55
Q

Outline hydrocarbon extraction and burning as a movement of carbon.

A
  • dead plants / animals runs into fossil fuels following burial. The pressure from multiple layers of sediment leads to an anoxic environment that allows decomposition to take place. When this is combined with heat from the Earth, the carbon in sugar molecules is rearranged to form other compounds eg petroleum (crude oil) or coal. When these fossil fuels are extracted from the ground and then burnt, CO2 and water are released init the atmosphere.
  • cement manufacture contributes CO2 to the atmosphere when calcium carbonate is heated, producing lime and carbon dioxide. CO2 also produced by burning the fossil fuels that provide the heat for the cement manufacture process. (Cement industry process accounts for 5% of global anthropogenic CO2).
56
Q

Outline farming practices as a movement of carbon.

A

• when soil is ploughed, the soil layers invert, air is mixed in, and soil microbial activity rapidly increases. -> This results in soil organic matter being broken done much more rapidly, and carbon is lost from soil into atmosphere.
Also, emissions from tractors increase CO2 levels in the atmosphere.

  • largest source of carbon here: ENTERIC FERMENTATION - when methane (CH4) is produced by livestock during digestion and released via belches (accounted for 39% of this sector’s global greenhouse gas outputs in 2011).
  • 44% of agriculture related greenhouse age inputs occurred in Asia in 2011 (maybe due to rice paddies that generate methane).
57
Q

Outline land use change (deforestation) as a movement of carbon

A
  • most deforestation is due to the need for extra agricultural land (usually using slash and burn method).
  • also by logging (who build roads to access more remote forests, in turn leading to more deforestation). Could also be unintentional: eg wildfires, or subsequent overgrazing, which may prevent the re-establishment of young trees.
  • about the same size as Greece in world forests are cut down each year.
  • but, planting of trees has meant forests are established or expanded onto agricultural land; reducing the net total loss of forest area. At present, we’re losing about 200km2 of forest each day.
58
Q

Outline land use change (urban sprawl) as a movement of carbon.

A
  • now, over 1/2 of world population lives in urban areas, (expected 60% by 2030). As cities grow, land use changes from natural to built up environment. Therefore, the CO2 emissions resulting from energy consumption for transport, industry and domestic use, added to the CO2 emitted in the cement manufacture required for infrastructure have increased.
  • in total, cities are projected to be responsible for 56% of the global increase in carbon emissions between 2012-2030.
59
Q

Carbon sequestration is a movement of carbon. But what is it?

A

Capturing CO2 from the atmosphere and putting it into long term storage.
Two types: geologic sequestration and terrestrial sequestration.

60
Q

Geological sequestration is a movement of carbon. Outline how.

A

CO2 is captured at its source (eg power plants), then injected in liquid form into underground storage (eg depleted oil and gas reservoirs).

Also, the ocean is a good carbon system because if its size - the carbon sequestered is ‘sunk’ within weeks or months of being captured. Once in the deep ocean, it’s in a circulation system for 1000s of years.

61
Q

Terrestrial sequestration is a movement of carbon. Outline how.

A

The use of plants to capture CO2 from the atmosphere and then store it as carbon in the stems and roots of the plants as well as in the soil.

The aim is to develop a set of land management practices that maximises the amount of carbon that remains stored in soil and plant material for the long term.

62
Q

What are the disadvantages of terrestrial sequestration as a movement of carbon?

A

Eg, a forest planted to capture carbon might lose that carbon back to the air in a catastrophic forest fire, or if the forest suffers disease.

Therefore land based sequestration plantations require active monitoring and management for their lifetime, and the carbon within those systems is never fully removed from the atmospheric system.

63
Q

What is the impact on the land of the constantly changing carbon budget?

A

This has been subject to intense research - but results are unclear because the study has been over a short time period. Also because there are so many possible variables (both human and physical).

64
Q

How has carbon changed over time in oceans?

A

Many of the observed physical and chemical changes in the ocean are consistent with increasing atmospheric CO2 and a warming climate.

65
Q

Outline the 5 main effects on the ocean from the constantly changing carbon budget.

A
  • ocean acidification
  • ocean warming
  • melting sea ice
  • ocean salinity
  • sea level rise
66
Q

Ocean acidification is an impact on the ocean due to the constantly changing carbon budget. Outline this.

A
  • 30% of the CO2 that’s been released into the atmosphere has diffused into the ocean through direct chemical exchange. This dissolving CO2 creates carbonic acid (thus decreasing the pH of ocean).
  • carbonic acid reacts with carbonate ions in the water to form BICARBONATE. However, these carbonate ions are used by animals (eg coral, phytoplankton) to create their CaCO3 shells. Therefore, with less carbonate available, the animals needs to expend more energy to build their shells - so shells end up thinner and more fragile.
  • coral reefs provide food and livelihood security for 500m people worldwide - therefore significant reef loss (and consequent fall in marine biodiversity) threatens the survival of coastal communities through reduced food availability and a reduced capacity of coastlines to buffer the impact of sea level rise.
67
Q

Ocean acidification is an impact on the ocean due to the constantly changing carbon budget. What is the positive of this?

A

The more acidic the sea water is, the better it dissolves CaCo3 rocks (chalk, limestone). Over time, this allows the ocean to soak up excess CO2 - because the more acidic water will dissolve more rock, release more carbonate ions and increase the ocean’s capacity to absorb CO2.

68
Q

Ocean warming is an impact on the ocean due to the constantly changing carbon budget

A

• warmer oceans (product of climate change) decreases the abundance of phytoplankton; which grow better in cool, nutrient rich waters.
This limits the ability to take carbon from the atmosphere through the biological carbon pump and therefore lessens the effectiveness of the oceans as a carbon sink.

  • ocean warming kills of symbiotic algae which coral needs to grow, leading to bleaching and eventual death of reefs.
  • however, an increase in CO2 could increase the growth of phytoplankton by fertilising new species of phytoplankton and ocean plankton that take CO2 directly from the ocean.
69
Q

Melting sea ice is an impact on the ocean due to the constantly changing carbon budget. Outline how.

A
  • when sea ice melts, it shows global warming. (Also displayed feedback mechanism - highly reflective ice is replaced by more heat absorbent water. When ur starts to melt, the ocean can absorb more sunlight, which in turn amplifies the warming that caused it to melt in the first place).
  • sea ice provides unique habitats for algae (they appear in more conc forms and with more fat content in the ice).
    Therefore, the loss of algae affects marine predators all the way up the food chain (from krill to seals, walruses, polar bears)
    Furthermore, animals eg polar bears rely on sea ice to get their main food source of seals, and can no longer travel upon it.
70
Q

Ocean salinity is an impact on the ocean due to the constantly changing carbon budget.

A

• decrease in ocean salinity in deep North Atlantic. Probs because of higher levels of precipitation - this leads to higher river runoffs that eventually reach the sea.
Also higher temps, which are causing melting of Greenland ice sheet and many alpine glaciers: also leads to increase in freshwater reaching oceans.

71
Q

Sea level rise is an impact on the ocean due to the constantly changing carbon budget

A

Sea levels have been rising 3.5mm since 1990. Caused by:

  • MELTING OF TERRESTRIAL ICE: (recently, higher temps have lead or an increased rate of summer melting and drop of snowfall in the shorter winters. This imbalance = significant net gain in water entering the oceans from rivers, against evaporation from the ocean. Furthermore,e the ice sheets of Antarctica and Greenland are moving more quickly towards the oceans due to increased amount of meltwater lubricating their bases).
  • THERMAL EXPANSION: (when water heats up, it expands. So about 1/2 the past century’s SLR is due to ocean’s having a greater volume and so occupying more space.
72
Q

What are the two causes of sea level rise?

A
  • melting of terrestrial ice

- thermal expansion

73
Q

Why is the greenhouse effect good?

A

Because without greenhouse gases, the earth would be a frozen -180C. But with too many, the Earth would be too hot at around 400C.

74
Q

What do greenhouse gases do in the greenhouse effect?

A

They absorb a wide range of energy (including infrared (heat)) emitted from the Earth, and then re-emit it.

This re-emitted heat travels in all directions, but some returns to Earth which heats the surface.

75
Q

What is the problem that we face due to the greenhouse effect?

A

The enhanced greenhouse effect - which is the impact on the lunate from the additional hear retained due to the increased amounts of CO2 and other greenhouse gases that humans have released into the Earth’s atmosphere since the Industrial Revolution.

This causes radiactive forcing.

76
Q

What is radiactive forcing?

A

Caused by the enhanced greenhouse effect this is the difference between incoming solar energy absorbed by the Earth and the energy radiated back into space.

77
Q

What happens if the balance between incoming and outgoing infrared radiation from the sun is anything other than 0?

A

There is radiactive forcing, and there’s some warming or cooling

g: wcc (25 decks)

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