Carbon cycle EQ1 Flashcards
biochemical carbon cycle
the continuous transfer of carbon from one store to another, through the process of photosynthesis, respiration, decomposition and combustion.
carbon is exchanged among
the biosphere, pedosphere, lithosphere, hydrosphere, and atmosphere of the Earth
biosphere - living things
- 560 billion metric tons of carbon
- 0.0012% of all carbon
- forests like the amazon
atmosphere - air
- 750 billion metric tons
- 0.0017% of all carbon
- greenhouse gasses
pedosphere - soil
- 0.0031% of all carbon
- organic matter
fossil fuels
- 4000 billion metric tons
- 0.004% of all carbon
hydrosphere - water
- 38000 billion metric tons
- 0.038% of all carbon
- sea water
Lithosphere - crust+mantle
- 99.9% of all carbon
lithosphere def
rigid outer part of the earth, consisting of the crust and upper mantle
fluxe
action or process of flowing in or out
carbon from the atmosphere can be sequestered into sedimentary rocks or as fossil fuels. Carbon rich sedimentary rock forms in 2 ways …..
- from dead organic matterforming layers at the bottom of oceans
- calcifying marine life
Fluxes and Stores in the Carbon Cycle
- Forests
- Oceans
- Fossil fuels (eg coal)
- Sedimentary rocks (eg limestone)
thermohaline circulation
the movement of ocean currents due to differences in temperature and salinity in different regions of water
formation of shale/coal
- The remains of plants and animals sank to the bottom of rivers, lakes and seas and were covered with silt and mud.
- The remains continued to decay anaerobically and were compressed by further accumulations of dead organisms and sediment. The deeper the deposits, the more heat and pressure is exerted.
- When organic matter builds up faster than it can decay, layers of organic carbon become oil, coal or natural gas instead of shale.
formation of limestone
- Limestone is formed in ocean environments.
- Limestone started life as ocean sediments rich in calcium carbonate derived.
- The process of diagenesis occurs to convert the sediment into sedimentary rock.
example of one of earths largest carbon stores
the Himalayas, which started off as ocean sediments, rich in calcium carbonate. The upfolding formed mountains which are now weathered, eroded and transported back into the ocean.
Calcareous ooze
a calcium carbonate mud formed from the hard parts of the bodies of free-floating organisms.
chemical weathering flow diagram
- transfers carbon from atmosphere to hydrosphere and biosphere
- atmospheric carbon reacts with water vapour to form weak carbonic acid
- acid rain forms on condensation
- rain dissolves calcium carbonate in rocks
- produces carbon ions which get transfered into the sea
outgassing flow diagram
- release of trapped or stored gass from volcanic erruptions
- metamorphism occurs at subduction zones where sedimentary rocks turn into metamorphic rocks under extreme pressure
Positive feedback
occurs to increase the change or output: the result of a reaction is amplified to make it occur more quickly
negative feedback
occurs to reduce the change or output: the result of a reaction is reduced to bring the system back to a stable state eg combination of chemical weathering and outgassing
Carbon can be sequestered into oceans
Phytoplankton sequester atmospheric carbon during photosynthesis in surface ocean waters; carbonate shells/tests move into the deep ocean water through the carbon pump and through the action of the thermohaline circulation.
Carbon moves between the atmosphere, the surface water of the ocean and the deep water through three interconnected systems known as pumps:
- Physical pump
- Biological pump
- Carbonate pump
Carbon sequestration
the process of capturing and storing atmospheric carbon dioxide.
physical pump
- Cold water holds more carbon dioxide than warm.
- Cold water is denser than warm water so it sinks and is held under pressure by the weight of the water above it.
- This means there is a higher concentrations of carbon dioxide in the deep water of the ocean and at higher latitudes where the water is colder.
upwelling
old water is then forced to the surface in other areas of the ocean. Carbon dioxide is brought up to the surface where it might be released into the atmosphere or absorbed by phytoplankton
downwelling
The thermohaline circulation moves warmer water on the surface into cooler areas of the world. As the warm water cools, it absorbs more carbon dioxide and sinks to the deeper waters
biological pump
- Carbon dioxide can be consumed by phytoplankton, through the process of photosynthesis.
- Phytoplankton are at the bottom of the food chain for marine animals so the carbon is transferred up the chain.
- Respiration releases some carbon dioxide back into the atmosphere, though most of this carbon remains in surface waters and then is reabsorbed by phytoplankton.
- When marine animals die they fall to the ocean floor, where the carbon stored in their bodies is transferred to the deep ocean.
carbonate pump
- Chemical weathering can wash carbon-based molecules into the sea through river systems.
- Here, they react with carbon dioxide dissolved in the water to form calcium carbonate, which is used by some marine organisms to make shells.
- When these marine organisms die, they sink to the bottom of the ocean where they create a sediment rich in calcium carbonate (sedimentation).
- These form limestone.
terrestrial primary producers
Terrestrial primary producers sequester carbon during photosynthesis; some of this carbon is returned to the atmosphere during respiration by consumer organisms.
Biological carbon
carbon can be stored as dead organic matter in soils, or returned to the atmosphere via biological decomposition over several years.
soil
- Active soil microbes respire CO2 quickly
- If plants transfer more carbon into soil than is released via soil respiration, more carbon will get stored in the soil
- Microbes need energy: it comes from burning sugars, which in turn releases CO2.
- This CO2 can be used by plants covering the soil surface for photosynthesis and/or drift up to the air to join other CO2 molecules in the atmosphere.
solar radiation
- Light energy from the sun (short wave)
- Absorbed by earth and re-emitted as longwave energy (heat)
- Some escapes the atmosphere, but some is absorbed by greenhouse gases, warming the earth and its atmosphere
the enhanced greenhouse effect
If we add more greenhouse gases to the atmosphere, more of that longwave radiation will be trapped (and less will escape)
The planet will warm up more than it should do
Shortwave radiation
- 49.1% of incoming solar radiation is absorbed by the Earth
- 19.6% absorbed by the atmosphere
- 31.3% is reflected into space from the Earth’s surface and clouds
Longwave radiation
- 390 Wm2 (energy) radiated from the Earth as longwave radiation
- 40Wm2 goes straight out to space
The energy budget is balanced
Incoming energy equals outgoing energy, but the greenhouse gases ensure that the lower atmosphere, land and sea is warmed, albeit with a range of temperatures from tropical to polar.
Without greenhouse gases the Earth’s average surface temperature would be -6oC rather than +15oC
human implications of fossil fuels
Human activity has transferred considerable amounts of carbon from fossil stores, where fluxes are very slow, into the fast category, significantly disturbing the climate cycle. Whereas after an ice age it usually took the planet 5000 years to warm up again (by 4-7oC), the present warming rate is estimated to be eight times faster.
climate
- Changes in the thermohaline circulation - melting glaciers → reduced salinity → reduced downwelling
- Dry areas are likely to get drier and wetter areas are likely to see increased rainfall
- Rainfall patterns will become unpredictable
- Extreme weather events such as storms will increase.
hydrological system
- Glacial areas - Ice sheets and glaciers are melting which increases the risk of flooding for glacier-fed rivers.
- Meltwater adding to the oceans → sea level rise
- Increased precipitation → more floods
ecosystems
- Plants that are sensitive to temperature have declined → biodiversity in some biomes decreasing
- Areas of permafrost are no longer experiencing long seasons of frozen ground → impacts vegetation that is adapted to these conditions.
- Species migration to find correct conditions for survival
- Increased risk of extinction
- Sea level rise → loss of ecosystems in low lying regions
- Ocean acidification → coral bleaching
Positive Feedback in the Carbon Cycle
Permafrost thawing due to global warming:
- Higher temperatures thaw permafrost in tundra regions.
- Organic material in permafrost decomposes → releases CO₂ and CH₄.
- These are potent greenhouse gases → more heat trapped in atmosphere.
- Leads to further warming and more permafrost melt.
Result: A self-reinforcing loop accelerating climate change.
Negative Feedback in the Carbon Cycle
CO₂ fertilisation effect:
- Higher CO₂ concentrations stimulate plant growth (photosynthesis).
- Plants absorb more CO₂ from the atmosphere.
- This reduces atmospheric CO₂ levels over time.
Result: Helps counteract the initial rise in CO₂ – restoring balance.
