Paper 1 — Section C — Carbon Cycle Flashcards
What is the carbon cycle?
Movement of carbon between stores in the lithosphere, hydrosphere, biosphere and the atmosphere
It is a closed system as a whole, with subsystems that are open and have inputs + outputs
Define closed system
There are no external inputs or outputs of carbon to the earth so the total amount of carbon is fixed and finite
Define stores
Huge reservoirs where carbon is held. AKA known as pools, stocks and reservoirs
They function as sources and sinks
Define sources
Add carbon to the atmosphere
Define sinks
Remove carbon from the atmosphere
Define fluxes
Movement of carbon between stores from one store to another. AKA flows. They provide the motion in the carbon cycle
Define processes
Physical mechanisms which drive the fluxes between stores
Define reservoir turnover
Rate at which carbon enters and leaves a store, measured by the mass of a store divided by the fluxes
What are the 4 main carbon stores?
- Atmosphere
Gases i.e carbon dioxide and methane - Hydrosphere
Oceans, lakes, rivers etc which dissolve CO2 - Lithosphere
Carbonates found in rocks i.e limestone and chalk and fossil fuels - Biosphere
Living and dead organisms, most notably the worlds forests
What are the top 3 biomes with the most carbon stored?
- boreal forests
- tropical forests
- tropical savannahs
What are the stages during limestone formation, and how does limestone get eroded / transfer carbon for deposition on the seabed?
- Skeletons of marine creatures and formed marine phytoplankton absorb carbon through photosynthesis
- The remains accumulate on the seabed and compact into limestone over time
- *Limestone may also form from precipitation of calcium carbonate from salt, freshwater or evaporation of seawater
- Limestone rocks are vulnerable to chemical weathering (acid rain)
— weak carbonic acid dissolves the calcium carbonate - Erosion processes transfer dissolved carbon for deposition on the seabed
How long ago was most coal formed?
300-360 million years ago
How does peat form?
Where partial decomposition takes place: remains of plants receive no oxygen underwater. This incomplete destruction leads to the accumulation of peat
What is peat?
A fibrous, soft, spongy substance in which plants are easily recognisable. Contains large amounts of water (must be dried before use)
Therefore seldom used as heat source
What is lignite?
It is dark brown in colour and contains traces of plants like peat.
Found in many places but is only used when more efficient fuel isn’t available.
How is lignite formed?
Lignite forms when peat is subjected to increased vertical pressure from accumulating sediments
What happens when excess pressure is applied to lignite?
Further compaction and virtually all traces of plant life disappear to form bituminous coal
What is the order of stages before coal formation?
- Peat
- Lignite
- Bituminous, soft coal
- Anthracite
How old is oil / natural gas?
250-260 million years old
What did oil originate from millions of years ago?
Microscopic plants and animals living in the oceans.
These organisms absorbed energy from the sun, which was stored as carbon molecules in their bodies
What does higher pressure / temperature create compared to lower pressure / temp? (Think of non-renewables)
Natural gas versus lighter oil
What has caused the pockets and deposits of oil and gas in the earths lithosphere?
Tectonic Earth movements resulting from tectonic folding and faulting adjusted the relative positions of different layers of rock
Some fossil fuel deposits got trapped under impermeable rock layers (where we find them today)
How long will our current oil and natural gas reserves last?
60-90 years
Describe the 4 stages of chemical weathering (rainwater)
- During precipitation, rain falls to the ground and absorbs CO2
- This then makes it acidic (carbonic acid)
- Precipitation then reacts with calcium carbonate within limestone / chalk
- Finally, CO2 gets released back into the atmosphere, or calcium carbonate is transported by rivers back into oceans
Define volcanic outgassing
Where eruptions spewed gases from the Earths interior into the atmosphere
Describe the 3 stage process of volcanic outgassing
- Sedimentary rocks get formed
- These then move towards a convergent plate boundary over time
- The rock then gets subducted and CO2 gets released during CO2 eruptions
Where does volcanic outgassing occur?
- active or passive volcanic zone associated with tectonic plate boundaries
- divergent boundary volcanoes emit less CO2 because lava is basic (contains less gas)
- places with no current tectonic activity I.e hot springs and geysers
- direct emissions from fractures in the Earths crust
Describe the negative feedback loop regarding the regulation of the geological carbon cycle
- Increase in volcanic activity
- Rise in CO2 emissions and loss of carbon from rocks
- Temperature rises
- More uplift of air, condensation and rain
- More chemical weathering and erosion of rocks
- More ions deposited on ocean floors
- More carbon stored in rocks
-back to 1-
Define carbon sequestration
It is the process of capturing and storing atmospheric CO2 in plants, soils, oceans and geologic formations
What is a physical carbon pump?
It is a process which operates in oceans to circulate and store carbon
(Thermohaline circulation)
What is a biological carbon pump
The transfer of CO2 to marine organisms (phytoplankton) via photosynthesis, as they respire they consume carbon and release oxygen in the process
Most of the carbon dioxide taken up by phytoplankton is recycled near the surface. About 30% sinks into deeper waters before being converted back into carbon dioxide by marine bacteria.
1 peta-gram is worth how much carbon in grams?
1 billion
Which biome stores the most carbon?
Boreal (pine) forests
Name the 3 stores of carbon
- Terrestrial (lithosphere)
- Hydrosphere
- Atmosphere
Ocean sequestration: how much carbon do oceans store?
(Worlds largest carbon store)
- 50x greater than the atmosphere
- 93% stored in undersea algae, plants, coral
- 38,000-40,000bn metric tonnes in CO2 in the ocean itself
- 66-100mn-bn in marine life
What is the thermohaline circulation?
The component of general oceanic circulation which is controlled by horizontal differences in the temperature and salinity gradient
(Physical pump) Describe the stages of the thermohaline circulation, mentioning how it stores and releases carbon
- Water in polar regions is colder and more saline, therefore denser than in the tropics.
- As a result of this, it sinks (downwelling) to the seabed, where dissolved carbon dioxide moves in slow-moving, deep currents for hundreds of years (carbon store)
- The cold sinking water draws in the warmer water from the oceans surface above (draws water across surface from the tropics)
- This movement of water from the tropics then draws cold water up (upwelling) from the seabed to be warmed again — as it rises towards the surface, dissolved CO2 is released back into the atmosphere
(Biological pump) Which organisms sequester CO2?
Phytoplankton
(Biological pump) Where are phytoplankton typically found and why?
They float near the ocean surface to access sunlight for photosynthesis
Before sinking deeper into the ocean through the carbonate pump and action of the thermohaline circulation
(Biological pump) How much carbon do phytoplankton sequester each year?
2 billion metric tonnes
What are the 3 pump categories?
- Biological pumps
- Carbonate pumps
- Physical pumps
(Physical pump) What does warm water do to CO2?
Release it
(Physical pump) what does cold water do to CO2?
Absorbs it
(Carbonate pump) what do marine organisms use calcium carbonate for?
To form outer shells / skeletons I.e plankton, coral, oysters
What is terrestrial sequestration?
Where primary consumers eat the primary producers i.e bugs, beetles and herbivores (sequestered carbon passes on, becoming a part of their fats and proteins after digestion)
In turn, biological decomposers I.e worms, bacteria, insects feed on dead plants / animals and then release carbon back into the atmosphere through respiration
Where can biological carbon be stored?
In soils in the form of dead organic matter (quicker process in tropical soils, slower process in tundra)
Alternatively
Returning it to the atmosphere due to decomposition over several years
Why don’t soil stores develop in rainforests?
Rainforest soil is thin and infertile due to the humidity
As litter and dead wood decay, they are recycled so quickly that a soil store doesn’t develop
How much CO2 does the rainforest absorb and how much earth do they cover?
They account for 30% and only cover 17% of the earths surface
Why do plants sequester more carbon in the summer?
They have more leaves and so more carbon can be sequestered
Do CO2 levels rise or fall in summer months?
Rise
Define what a green plant is
Primary producers which use solar energy to create biomass
How much more carbon is sequestered than released?
1000x more
What is a carbonate carbon pump?
A process where sediment gets formed from dead organisms that fall to the ocean floor, especially their shells which are all rich in calcium carbonate
— this carbon becomes part of deep ocean currents or compact and form limestone
What are the 2 types of greenhouse effect
- Natural greenhouse effect
- Enhanced greenhouse effect
Define the natural greenhouse effect
The natural process whereby the earths surface warms up at a sustained rate
Define the enhanced greenhouse effect
The natural greenhouse gas process which has gotten exacerbated by anthropogenic (human) activities
Name some human factors which have contributed towards the enhanced greenhouse effect
- burning of fossil fuels
- jet aircraft engines
- fertilisers and pesticides
- cattle farming
- solvents and cooling equipment
- deforestation
Describe the 4 stages of the natural greenhouse effect
- Short-wave radiation passes through the atmosphere
- Some short-wave radiation is absorbed and converted into long-wave radiation
- Some long-wave radiation is absorbed and re-emitted, heating up the earths mean temperature
- Some long-wave radiation is reflected and passes back into space
Name the 6 greenhouse gases
- Nitrous oxide
- Halocarbon
3+4. Ozone + water vapour - Methane
- Carbon dioxide
What is the most common greenhouse gas? (What%?)
CO2 - 89%
Why are greenhouse gases important?
They absorb and reflect back into the atmosphere some of the radiated heat — earth 16°C warmer because of them
Since when has the concentration of greenhouse gases increased by 25%?
1759 — industrial revolution
Since 1980s, 75% of CO2 emissions have come from the burning of fossil fuels
Where on the Earth are sun rays their strongest?
The equator
Where is solar radiation more dispersed / covers a larger area?
The poles
What colour terrain absorbs, and which reflects heat
Absorbs — black
Reflects — white
Which continents receive the highest rainfall?
South America, North America, Europe
Which continents recieve the least rainfall?
Middle East, Northern Africa
What is a climate feedback loop?
Knock on effect which feeds back into our climate (either +ve or -ve)
What is a negative feedback loop? (Climate change) + provide examples
Impact which offsets the prevailing change in climate.
Under global warming, this would create a cooling effect, balancing out the changes
I.e afforestation, less fossil fuels
What is a positive feedback loop? (Climate change)
Impact which increases the change in the climate.
Adds to global warming by creating further heating
I.e warming temps in arctic
How does weathering of rocks release carbon into the atmosphere?
Rocks on the land are broken down by carbonation weathering (when CO2 in the air mixes with rainwater to create carbonic acid — this aids erosion of rocks I.e limestone
This carbon is moved through the water cycle and enters oceans before being used by marine organisms to make their shells
How does the concentration of atmospheric carbon influence the natural greenhouse effect?
CO2 controls the amount of water vapour in the atmosphere and therefore the size of the greenhouse effect — as concentrations of CO2 rise, air temperatures go up and more water evaporates into the atmosphere which amplifies the greenhouse effect
What unit is used to measure the carbon fluxes between carbon stores?
Petagrams or gigatonnes of carbon annually
Which of the 4 is the largest carbon store?
Geological: over 100 million Pg of carbon in the lithosphere
How are sedimentary rocks formed? 4 steps
- Sediment is deposited in layers in a low-energy environment i.e seabed
- Further layers are deposited and sediment undergoes diagenesis
- Lower layers become compressed and chemical reactions cement particles together
- Lithification occurs
Define lithification
The conversion of loose, unconsolidated sediment into solid rock
Define diagenesis
Physical and chemical changes that occur during the conversion of sediment to sedimentary rock
Provide some characteristics about limestone rock / its relation with carbon / how is it formed?
- composed of calcium carbonate: 40% is carbon by weight
- 80% of lithospheric carbon is found in limestone
- limestone is formed when calcium carbonate is deposited on the ocean floor
Which physical landform forms one of the earths largest carbon stores, and why?
Himalayas:
These mountains originated as ocean sediments rich in calcium carbonate derived from crustaceans
These sediments have since been up folded, and eventually it’s carbon has been eroded and transported back to oceans
How can geological carbon be released into the atmosphere through acid rain?
CO2 in the atmosphere reacts with moisture to form weak carbonic acid. This reacts with surface minerals when raining, and slowly dissolves them
What does soil health often depend on?
The amount of organic carbon stored in the soil. The storage amount is determined by the balance between soils inputs and outputs
How can only a small amount of surface soil erosion have such a devastating impact on soil health / fertility?
Carbon is the main component of soil organic matter
> helps give soil its moisture-retention capacity, it’s structure and fertility
Healthy soil has a large surface reservoir of available nutrients which condition the productivity of ecosystems
What percentage of CO2 emissions are estimated to be remaining in the atmosphere since the Industrial Revolution?
50%!
What has the impact of additional CO2 being added to the atmosphere meant for the atmosphere? (Climate change)
- rise in global mean temperatures
- more precipitation / evaporation
- sudden shifts in weather patterns
- more extreme weather events
- some areas becoming wetter, some becoming drier
What do the implications of climate change mean for ecosystems?
- rising sea levels; increased glacial meltwater etc which threatens coastal cities
- decline in yield from ecosystems; decline in biodiversity, changes in dist. Of species, marine organisms threatened etc (coral bleaching)
What are the implications of global warming for the hydrological cycle?
Increased temperatures and evaporation rates which cause more moisture to circulate around the cycle
How do biological pumps circulate and store carbon?
- Phytoplankton and crustaceans absorb co2 into their shells
> essentially converts co2 into food for predators - most of this co2 gets recycled near the surface, but 30% sinks deeper into waters before being converted back into co2 by marine bacteria