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