Lecture notes

AQA A level Geography Notes: Physical Geography - The Carbon & Water Cycle

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Module
Unit 1 GEOG1 - Physical and Human Geography

Institution
AQA

Book
AQA Geography A Level

A* level notes on the global Carbon & Water cycle for the physical side of the AQA course. Topics covered include: CARBON CYCLE: - Stores - The Global Carbon Cycle: Transfers - Changes in The Carbon Cycle: Human & Physical Causes - The Carbon Budget - Water, Carbon And Climate Change - C...

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THE GLOBAL CARBON CYCLE

Stores:

THE GLOBAL CARBON CYCLE, WHAT:
• Carbon = basic element needed by all plants to survive (as well as N2, P + S)
• The recycling of carbon is therefore essential for life on Earth
Long term & short term stores:
• The main stores of carbon are the lithosphere (rocks + soil), hydrosphere (oceans),
cryosphere (snow + ice), atmosphere + biosphere (plants)
• A carbon sink = store that absorbs more carbon than it releases
• A carbon source releases more carbon than it absorbs
Flows/Processes:
• Process involved in transferring carbon between the stores e.g. photosynthesis takes CO2
out of the atmosphere + converts it into carbohydrates e.g. glucose within plants)

WHAT ARE THE MAIN STORES IN THE CARBON CYCLE:
1) Lithosphere
- 99.9+% of carbon on Earth = stored in sedimentary rocks e.g. limestone
- Marine sediments + sedimentary rocks = largest long-term store of carbon, with rocks
taking millions of yrs to form
- Fossil fuel deposits in lithosphere = 0.004%
o Hydrocarbons = important long-term stores of carbon → since industrial rev
combustion increase CO2 levels
2) Hydrosphere
o Ocean = 0.04% of earth’s carbon -> maj found in deep sea in form of dissolved inorganic
carbon
o A small amount is found at ocean’s surface where it’s exchanged with atmosphere
o CO2 absorbed directly from the air + rivers discharge carbon carried in solution
3) Biosphere
o Soil organic matter = Amount in billions of tonnes =1,500
o Carbon from rotting veg can remain in soils for 100s of years
o Deforestation land-use change + soil erosion can rapidly release the stored carbon
o Terrestrial plants
o Plants convert energy from Sun into carbohydrates that support life
o Plants can store carbon for many years + transfer it in to the soil
4) Atmosphere
o Atmosphere = 0.001% of earth’s carbon
o Atmospheric CO2 increased due to emissions from power stations, vehicles + deforestation
5) Cryosphere
a. Contains less than 0.01% of Earth’s carbon
b. Most carbon here = in soil in areas of permafrost

THE GLOBAL PATTERN OF VEGETAION CARBON STORAGE:
• Some regions e.g. Sahara Desert, have virtually no plant storage, others have flourishing
veg growth
• Carbon uptake = increasing in middle/high latitudes of the northern hemisphere
• Less C = absorbed in the tropics + southern hemisphere mainly due to drought

,The Global Carbon Cycle: Transfers
Wood = 50% carbon

THE CARBON CYCLE AT A LOCAL SCALE:
A terrestrial carbon cycle:
• When rock is exposed for the 1st time it is vulnerable to
processes of weathering
• As the rock is slowly broken down, carbon may be released,
often dissolved in water
• Over time, vegetation e.g. lichen + moss grows on the bare rock + carbon exchange starts to
take place, involving photosynthesis + respiration
• As organic matter is added, a soil develops that can support a wider range of plants
• Over 100s of years, plant species → more diverse, benefitting from supply of carbon in the
soil
This sequence of changes = vegetation succession
- A succession that relates to a specific
envo = sere
- Each stage in succession = a seral stage
- Llithosere = vegetation succession
occurring on bare rock
- Other seres = hydrosere (fresh water),
halosere (salt water), psammosere (sand
dunes)
- Climatic climax = when equilibrium is achieved
- The climax vegetation for a lithosere in the UK will usually be a deciduous woodland

WHAT ARE THE MAIN FLOWS/TRANSFERS OPERATING IN THE CARBON CYCLE:
1) Photosynthesis (fast carbon flow)
• Process whereby plants use light energy from. Sun to convert CO2 from air + water from soil
into carbohydrates (glucose)
2) Respiration (fast carbon flow)
• Chemical cellular process whereby glucose is converted into energy → used for growth
• CO2 then returned to atmosphere mostly by exhaled air
3) Decomposition (fast carbon flow)
• Organisms die → consumed by decomposers e.g. bacteria, fungi + earthworms
• During decomposition, carbon from their bodies is returned as CO2 to atmosphere
4) Combustion
• Organic material contains carbon → when burned in O2, converted to CO2, energy + water
• Co2 released into atmosphere, returning Carbon that might have been stored in rocks for
millions of years
5) Burial + Compaction
• Organic matter= buried by sediments + becomes compacted over time → millions of yrs
these organic sediments may form hydrocarbons e.g. coal + oil
• Limestone formed from organic calcium rich shells + coral, also stores large amount of
carbon
6) Carbon sequestration (slow carbon flow)
• Describes the transfer of carbon from atmosphere to plants, soils, rock formations + oceans
• Carbon capture + storage (CCS) = technological ‘capturing’ of carbon emitted from power
stations
7) Weathering
• When CO2 is absorbed by rainwater → mildly acidic carbonic acid
• Chemical reactions → rocks slowly dissolve with carbon being held in solution = carbonation

Penny Reversed Dan’s Car But Crashed Worryingly

, Changes in The Carbon Cycle: Physical Causes

IMPACTS OF NATURAL CLIMATE CHANGE:
• During Quaternary geological period (2.6M years
ago to present) global climates fluctuated
considerably between warm (interglacial) + cold
(glacial) period
• The causal relationship of trends for CO2 + temp
in figure 1 = debatable
• Increased CO2 enhances the greenhouse effect
causing temp rise
• But increased temp can = increased carbon e.g.
due to melting permafrost releasing methane

IMPACTS OF COLD (GLACIAL) CONDITIONS:
• Chemical weathering processes more active –
cold water can hold more CO2
• Decomposers less effective, so reduced carbon transfer to soils
• Less water reached the oceans, so less sediment transfer along rivers + less build-up of
sediments on the ocean floor
• Frozen soil over vast areas of land stopped transfers of carbon

IMPACTS OF WARM (INTERGLACIAL) CONDITIONS:
• Melting of permafrost in tundra regions e.g. Siberia → increased carbon emissions
• Enhances greenhouse effect → increased warming = example of positive feedback

IMACTS OF WILD FIRES:
• Wild fires release CO2 into atmosphere → spike in rising trend of carbon emissions
• Wild fires can turn forests from being a carbon sink to being a carbon source

IMPACTS OF VOLCANIC ACTIVITY:
• Volcanic activity releases CO2 that has been trapped for millions of yrs in rocks beneath crust
(380m tonnes/yr-> in comparison human activities emit about 30billion tonnes of CO2/yr,
mainly as due to burning fossil fuels)

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