6.1 - The carbon cycle and planetary health Flashcards
What is the carbon cycle?
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
What are the main carbon stores?
Terrestrial (lithosphere and biosphere)
Atmospheric
Oceans (hydrosphere)
When is the carbon cycle balanced?
It is in equilibrium when the sources equal the sinks.
What does anthropogenic mean?
environmental change caused by humans
What are the units used to measure stores of carbon?
Petagrams (Pg) or Gigatonnes (Gt) which are both equivalent to 1 billion tonnes
What are the 2 main components of the carbon cycle?
Slow moving geological carbon cycle (carbon stores in rocks and sediment)
Fast moving biological carbon cycle (carbon stores in vegetation, soils and the atmosphere)
What are the long term and short term carbon stores?
Long term = crustal/terrestrial/geological and oceanic (deep)
Short term = terrestrial soil and ecosystems, oceanic (shallow), atmospheric
Where is most of Earth’s carbon?
In geological stores, resulting from the formation of sedimentary carbonate rocks in the ocean and biologically derived carbon in shale, coal and other rocks
How is carbon stored in limestone and shale?
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)
How is carbon stored in fossil fuels?
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
What happens in chemical weathering of the geological carbon?
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
What happens in volcanic outgassing, where does it occur?
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
How is the geological carbon cycle regulated?
Via negative feedback - takes a few hundred thousand years to rebalance
What is carbon sequestration
transfer of carbon from atmosphere -> other stores
-e.g. plant sequesters carbon when it photosynthesises and stores the carbon in its mass
What is a carbon cycle pump, what are the 3 key pumps?
Processes operating in oceans to circulate and store carbon.
Biological, carbonate and physical
What is thermohaline circulation?
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
What is the biological pump?
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
What is the carbonate pump?
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
What is the physical pump?
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
What are the 5 distinct phases of thermohaline circulation?
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
What happens in terrestrial sequestration
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.
What is marine snow?
A shower of organic material (defecation and dead organic matter) falling from upper waters to the deep ocean
Explain how soil is a store of carbon
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.
What is the capacity of soil to store organic carbon determined by?
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
Why is it important to have a balanced carbon cycle?
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
What is the greenhouse effect? *
Earth’s natural temperature control system that relies on greenhouse gases
-31% -> carbon reflected by clouds
-remaining 69% -> absorbed
(greenhouse gases) - co2, methane
How has CO2 volume changed in recent years?
CO2 has increased in volume by 40% in the past 300 years
What does the natural greenhouse effect influence?
Greenhouse gas increases raise temperature, which in turn affects precipitation patterns
What is the importance of photosynthetic organisms?
They help to keep CO2 levels relatively constant, therefore regulating the composition of the atmosphere
What is soil health dependent on?
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)
Why is carbon in top soil and normal soil important, what effect does soil erosion have on this?
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
How has fossil fuel combustion changed in recent decades?
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
How has fossil fuel combustion altered the balance of carbon pathways and stores?
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
What are the implications of fossil fuel combustion for the climate?
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
What are the implications of fossil fuel combustion for ecosystems?
-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
What are the implications of fossil fuel combustion for the hydrological cycle?
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
What are the 3 forms of carbon in the carbon cycle
-inorganic - found in rocks as bicarbonates, carbonates
-organic - found in plant material, living organisms
-gaseous - found as co2, ch2
what are fluxes
movement/ transfer of carbon between stores
What is a carbon sink
any store which takes in more carbon than it emits
-e.g. tropical rainforest
What is a carbon source
any store that emits more carbon than it stores
-e.g. damaged tropical rainforest
Name the 4 types of stores that carbon is present in
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
Name the 6 main carbon stores
-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
Name the 6 fluxes within the carbon cycle
-photosynthesis
-respiration
-combustion
-decomposition
-diffusion
-sedimentation
-weathering and erosion
-metamorphosis
-volcanic outgassing
Explain how photosynthesis is a flux within the carbon cycle
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
Explain how respiration is a flux within the hydrological cycle
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
Explain how combustion is a flux
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.
Explain how decomposition is a flux
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.
Explain how diffusion is a flux
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.
Explain how sedimentation is a flux
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.
Explain how weathering and erosion is a flux
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
Explain how metamorphosis is a flux
– Extreme heat and pressure forms metamorphic rock, during which some
carbon is released and some becomes trapped.
Explain how volcanic outgassing is a flux
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
variations in the carbon cycle
Give a brief description of the thermohaline circulation process
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.
Why is the thermohaline circulation important in terms of regulating climate, minimising climate change
-as colder the water, the more CO2 is absorbed
-so if ocean temps ^ -> oceans absorb less co2 -> accelerating climate change -> more ocean warming
Name the 2 ways carbon fluxes due to terrestrial
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.
What is required to maintain stable average temperatures
constant levels of co2
What does the enhanced greenhouse effect mean and why is it bad
human activities (fossil fuels, coal, oil) generate ^ greenhouse gases
-these gases trap more heat ^ earth’s surface temperature
Name 6 human activites which has led to more carbon being released into atmosphere and less carbon being absorbed
-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
Name the 5 implications of the enhanced greenhouse effect
-temperature ->
-climate ->
-precipitation ->
-ecosystems ->
-hydrological cycle ->
pg. 88-93
How do the 3 carbon cycle pumps interlink
-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
