Carbon EQ1 - 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?
Processes and actions associated with human activity
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
What are the key processes in the geological carbon cycle?
- mechanical, chemical and biological weathering
- decomposition
- transportation
- sedimentation
- metamorphosis
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 are the 2 main geological processes moving carbon?
- chemical weathering of rock
- volcanic outgassing at ocean ridges and subduction zones
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 sequestrating?
The natural storage of carbon by physical or biological processes such as photosynthesis
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?
The global system of surface and deep water ocean currents driven by temperature and salinity differences between areas of the ocean
What is the biological pump?
The organic sequestration of CO2 to oceans by phytoplankton. Phytoplankton have high NPP and are the base of the marine food web, carbon is then passed up the food chain, releasing CO2 back into the water and atmosphere (respiration). Some decompose and reach ocean floor
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?
Based on oceanic circulation of water (thermohaline circulation). 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. CO2 accumulated at surface taken down with cooler water.
What are the 5 distinct phases of thermohaline circulation?
- main current begins in polar oceans where water is cold, sea ice forms, water gets saltier, increases in density and sinks
- 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 is the time scale of ocean sequestration?
CO2 gas exchange flux between oceans and atmosphere operates on timescale of several hundred years
What is the time scale of terrestrial sequestration?
Shortest time scale - only seconds, minutes or years
What happens in terrestrial carbon cycle?
Primary producers take CO2 out of atmosphere via photosynthesis (terrestrial sequestration) and release some back via respiration. When consumers eat plants, carbon becomes part of biomass. Microorganisms and detritus feeders feed on waste material from animals and carbon becomes part of them - released via respiration.
What is the role of phytoplankton in the ocean food web and carbon cycle?
Form the base of the aquatic food web (primary producers)
Carbon cycle - consumer CO2 on a scale equivalent to forests, part of biological carbon pump
What is marine snow?
A shower of organic material (defecation and dead organic matter) falling from upper waters to the deep ocean
How do terrestrial carbon fluxes vary?
- diurnally (during day = positive flux, at night = negative flux)
- seasonally (winter = more CO2, spring = less CO2 as plants begin to grow again)
What happens to biological carbon?
Either stored in dead organic matter in soil, or returned to atmosphere via biological decomposition
What are the 2 sources of carbon in soils?
- arid and semi arid soils contain inorganic carbon
- organic carbon from plant photosynthesis and subsequent decomposition
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
How is the carbon balance in soils regulated?
Plant productivity, microbial activity, geology, erosion, climate and the amount of upward and downward (leaching) water movement in the soil
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
Driven by incoming shortwave solar radiation, about 70% of which is absorbed - and of this, 70% is then re-radiated to space as longwave radiation. However, a large proportion of the longwave radiation is re-radiated to the surface again by greenhouse gases
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 and the temperature
Where are the areas of highest NPP on land and in the oceans?
On land - in areas that are warm and wet (carbon storage is also high in areas that have permafrost such as tundra)
In the oceans - in shallower waters, allowing higher photosynthesis and in places receiving high nutrient inputs
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)
What are the three main carbon/nutrient stores in soils?
Biomass
Litter
Soil
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?
Biomes most at risk = Arctic and coral ecosystems. Direct influence on changing services of ecosystems and biodiversity. Coastal ecosystems will be under risk for centuries.
Some positives = cool moist regions like UK could provide habitats for additional species
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
