Unit 4: Carbon Cycle Flashcards
(34 cards)
What is the Carbon Cycle?
The Carbon Cycle is a biochemical cycle by which carbon moves from one part of the planet to another.
How much carbon is stored in the atmosphere?
Around 750 billion metric tons (gigatons, or Gt) of carbon is stored in the atmosphere.
• About 0.001% of the Earth’s total carbon is stored in the atmosphere.
• The two main carbon-containing gases in the atmosphere are:
• Carbon dioxide (CO₂)
• Methane (CH₄)
(l) These gases are collectively known as greenhouse gases.
(m) The increase in atmospheric carbon (36% over 100 years) is due to human activities, especially:
• Burning fossil fuels (coal, oil, gas)
• Deforestation
• Industrial processes
What is the Pedosphere?
The pedosphere is the outermost layer of the Earth made up of soil. It contains about 0.003% of Earth’s carbon.
• Peat is partially decomposed organic matter found in waterlogged, anaerobic conditions.
• About 50–60% of peat is made from carbon.
(p) If buried and subjected to heat and pressure over millions of years, dead organic matter can transform into fossil fuels (coal, oil, natural gas).
How much carbon is stored in the Hydrosphere?
The hydrosphere stores about 0.0076% of global carbon, which is around 38,000 billion metric tons (Gt).
• The hydrosphere contains significantly more carbon than the atmosphere, pedosphere, and biosphere combined.
• About 90% of carbon in oceans is in the form of bicarbonate ions (HCO₃⁻).
What is the Fast Carbon Cycle?
The fast carbon cycle involves the quick movement of carbon (over days to decades) through:
• the atmosphere,
• biosphere (plants and animals),
• surface ocean.
Key processes include:
• Photosynthesis (plants absorb CO₂),
• Respiration (release of CO₂),
• Decomposition, and
• Combustion of organic matter.
The fast carbon cycle is largely the movement of carbon through life forms on earth: the biosphere.
The time it takes carbon to move through the fast carbon cycle is measured in the life span of a plant or animal.
Between 1000-100,000 million metric tonnes of carbon move through the fast carbon cycle every year through all life forms.
What is the Slow Carbon Cycle?
The slow carbon cycle involves the long-term movement of carbon (over millions of years) through:
• the lithosphere (rocks and sediments)
• deep oceans.
Key processes include:
• Weathering and erosion of rocks,
• Sedimentation of carbonates,
• Formation of fossil fuels, and
• Volcanic activity releasing CO₂ back to the atmosphere.
What is carbonation and how does it contribute to the slow carbon cycle?
Carbonation is a chemical weathering process where carbonic acid (formed from CO₂ and rainwater) reacts with calcium carbonate in rocks (like limestone), slowly dissolving them and releasing carbon into rivers and oceans.
This moves carbon from the atmosphere to the lithosphere.
Which rock type is most affected by carbonation, and what is the result?
Limestone (calcium carbonate) is most affected.
The result is the release of calcium and bicarbonate ions, which are transported to the ocean, contributing to the formation of marine carbonates and locking away carbon for millions of years.
How is carbon sequestered on the ocean floor in the slow carbon cycle?
Carbon is sequestered when marine organisms (like plankton) die and their calcium carbonate shells sink to the ocean floor, forming sedimentary rock.
This locks away carbon for millions of years.
What type of rock forms from carbon sequestration on the ocean floor, and what does it store?
Sedimentary rocks like limestone and chalk form from compacted shells and skeletons. These rocks store carbon long-term, making them a major reservoir in the lithosphere.
How do tectonic processes return carbon to the atmosphere?
Tectonic activity causes subduction of oceanic plates, taking carbon-rich sediments deep into the Earth. This carbon is then released into the atmosphere through volcanic eruptions as carbon dioxide (CO₂).
Why are volcanic eruptions important in the slow carbon cycle?
Volcanic eruptions release carbon dioxide stored in the Earth’s interior back into the atmosphere, maintaining the long-term balance of the carbon cycle over geological timescales.
At the bottom of the ocean carbonate rich sediments accumulate (carbon sequestration) due to?
• Bicarbonate from chemical weathering being transferred by rivers in to the ocean
• Biological carbon from the accumulation of dead marine organisms (this is explained
in detail in the fast carbon cycle)
• Over millions of years these sediments will compact to from rocks (a process known
as lithification) that make up the upper layer of the oceanic crust. It is estimated
that sediments at the bottom of the oceans contain millions of Gigatons of carbon
making it the largest stores of carbon.
What happens to the carbon stored on the ocean floor?
• In subduction zones at convergent plate boundaries some of the carbon sediments are converted into magma which may result in volcanic eruptions, emitting CO2 back into the atmosphere.
Each year about 200 million tons of CO2 are released into the atmosphere by volcanoes.
What is diffusion in the context of the carbon cycle?
Diffusion is the movement of carbon dioxide (CO₂) between the atmosphere and the ocean surface. CO₂ dissolves into the ocean and can also return to the atmosphere, depending on concentration gradients.
How does diffusion help regulate atmospheric CO₂?
Diffusion allows oceans to absorb excess CO₂ from the atmosphere, acting as a carbon sink, or release CO₂ back, helping to balance global carbon levels on short timescales (days to years).
How does photosynthesis play a role in the fast carbon cycle?
Photosynthesis removes CO₂ from the atmosphere. Plants absorb CO₂ and sunlight to produce glucose, storing carbon in biomass, and releasing oxygen.
What roles do respiration and decomposition play in the carbon cycle?
• Respiration by plants and animals releases CO₂ back into the atmosphere.
• Decomposition of dead organisms by microbes also releases carbon as CO₂ (or methane in anaerobic conditions), recycling it into the fast carbon cycle.
What is combustion in the carbon cycle?
Combustion is the burning of organic matter (like fossil fuels or biomass), which releases carbon dioxide into the atmosphere rapidly. It’s a major anthropogenic (human-caused) source of CO₂.
How has human activity altered the natural combustion process?
Humans have increased combustion through fossil fuel use (coal, oil, gas), adding large amounts of stored carbon to the atmosphere and intensifying the greenhouse effect and climate change.
What is the Physical (inorganic) Pump in diffusion?
The physical (inorganic) pump: movement of dissolved CO2 around the ocean CO2 can be moved around the ocean by thermohaline ocean currents, which form due to variations in ocean temperature and salinity (salt content):
• Carbon can be transferred from the surface to the deep ocean in areas where cold dense surface waters sink known as ‘downwelling’ - usually in Polar regions
• Carbon can be transferred from the deep ocean to the surface in areas where deep waters rise known as ‘upwelling’
- usually in Equatorial regions
What is the Biological (organic) Pump in diffusion?
The biological (organic) pump: a major source of carbon sequestration, driven by ocean phytoplankton absorbing CO2 via photosynthesis
• Diffusion of CO2 in to ocean surface
• Phytoplankton photosynthesise and use a diffused CO2 storing it in new biomass
• As part of the ocean food chain phytoplankton are eaten by zooplankton which in turn are eaten by other marine organisms, passing the carbon in carbohydrates.
• When organisms respire they release CO2 some of which will pass back to the atmosphere
• Marine organisms die and sink to seafloor adding to carbon-rich sediments on the sea floor
• Over millions of years organic carbon-rich sediment can form fossil fuels (oil and gas) note this is long carbon cycle
What is Photosynthesis?
Photosynthesis is a biochemical process operating in plants that converts CO2 and water into
carbohydrates (glucose) and oxygen:
What is Respiration?
• is a chemical reaction that happens in all living cells,
including plant cells and animal cells.
• It is a process in which energy is released from glucose so that all
the other processes needed for life can happen.
• CO2 is released back into the atmosphere as a by-product of
respiration.
• Just like photosynthesis rates of respiration will vary across the
planet
