6.2 biological processes sequestering carbon Flashcards
oceanic carbon cycle (store and flux)
the oceans are the earths second largest carbon store. (the store of carbon is 50x greater than the atmosphere)
- most of the oceanic crust is stored in marine algae, plants and coral: the rest occurs in dissolved form
- the volume and speed of the fluxes moving carbon into and out of the oceans is the 2nd largest after photosynthesis and respiration.
biological sequestering: the three types of carbon pump
compared to its geological counterpart, biological sequestering operates on much shorter timescales, from hours to centuries.
once dissolved into surface sea water via diffusion, CO2 can enter the carbon cycle through three ways.
TYPES OF CARBON PUMPS:
1. Biological Pump
2. Physical Pump
3. Carbonate Pump
biological pump
- the marine plant phytoplankton sequesters atmospheric carbon during photosynthesis in surface ocean waters. this effectively converts CO2 into food for zooplankton and their predators.
(50% of global photosynthesis is by phytoplankton- important flux!!!)
physical and chemical pumps
physical: (link to thermohaline circulation)
- these move carbon compounds to different part of the ocean in downwelling (cold sinking water) and upwelling currents.
- downwelling currents brings dissolved CO2 down into the deep ocean, once arrived it moves in slow deep ocean currents, staying for 100s of yrs.
- eventually these currents return to the surface by upwelling. the cold water warms as it reaches the surface- some of the dissolved CO2 is released back into the atmosphere
chemical:
- these form sediments from dead organisms that fall to the ocean floor- calcification (esp. hard outer shells and skeletons rich in calcium carbonate)
thermohaline circulation
= the global system of surface and deep ocean currents driven by temperature and salinity differences between different parts of the ocean.
THINK OF IT LIKE A CONVEYOR BELT:
- warm water is carried from within the tropics to the poles where it cools and is heavy enough to sink
when sea water cools it sequesters more via diffusion
- when it returns to the surface it warms up again and loses some of the CO2 back to the atmosphere (acts as a physical pump by moving oceanic carbon around the planet (food chains depend on it))
- also helps biological and carbonate pumps move carbon rich water down into deep oceans to be sequestered
terrestrial sequestering
PLANTS (primary producers in an ecosystem) sequester carbon out of the atmosphere during photosynthesis, !!carbon enters the food chains and nutrients cycles of terrestrial ecosystems this way!!
ANIMALS consume plant matter and carbon becomes part of their fat and protein. respiration returns some of this carbon back to the atmosphere. waste from animals is eaten by micro-organisms and detritus feeders (eg beetles)
when plants and animals die their remains fall top the ground and carbon is released into the soil.
timescale variation of fluxes within terrestrial ecosystems
carbon fluxes within ecosystems vary on 2 timescales:
DIURNALLY: during the day, fluxes are positive from the atmosphere into the ecosystem. (reverse applies at night: as photosynthesis does not occur but respiration does)
SEASONALLY: during WINTER CO2 concentrations INCREASE because of low levels of plant growth: little deciduous leaf reducing photosynthesis (outputs are larger than inputs). the arrival of spring reduces CO2 levels, plants grow and begin to sequester carbon (by SEPTEMBER carbon levels are LOWEST after an entire summer of sequestering carbon)
terrestrial carbon stores
all living organisms contain carbon (human body 18% carbon by weight) they store a very small amount of terrestrial carbon
plants also store terrestrial carbon but SOILS are the largest carbon stores, storing 20-30% of total global carbon!!!
vegetation= 18.8% of terrestrial carbon
soils= 81.2% of terrestrial carbon
they sequester about TWICE the quantity of carbon as the atmosphere. how????
they sequester carbon through litter-fall of leaves, branches, whole trees, decaying animals etc.
factors affecting carbon storage in soils
the actual amount of carbon stored in soils depends on:
- climate
temperature and precipitation levels determine plant growth and decomposition: rapid decomposition occurs in warm, wet regions so carbon storage is LESS there, boreal forest soils store twice as much as tropical rainforest soils: decomposers do not respire: ground is frozen) - vegetation cover
this affects supply of dead organic matter - soil type
clay protects carbon from decomposition, clay rich soils have a higher carbon content - land use
cultivation and other forms of soil disturbance increase the rate of carbon loss
since 1850 removal of natural vegetation for agriculture has meant 40-90 Gt of stored carbon has been lost globally
(new no till/ conservation agriculture is a method of improving soil health and carbon storage: no ploughing or breaking of soils= better root systems and higher humus and carbon content)
significance of different biomes: tropical rainforests
- tropical rainforests
- high inputs and high outputs!
produces and stores billions of tonnes of carbon each year, all tropical rainforests contain up to 25% of the worlds carbon
THREATS: deforestation- if entire amazon rainforest was lost it would be equivalent to up to 140 yrs of all human induced CO2 emissions
significance of different biomes: wetlands
- wetlands and peat lands
- holds 20-30% of total soil carbon despite occupying 5-8% of its land surface.
it can sequester carbon up to 55x faster than rainforests
THREATS: more than 1/3 of these carbon storing systems have been destroyed since 1970 (a rate 3x faster than forests)
significance of different biomes: tundra soils
- tundra soils
- moderate/ low inputs and little/ no outputs!
typically has been called a carbon sink due to ground being frozen almost all year around: frozen ground traps the organic matter and carbon the summer season produces: plant remains can remain trapped for several thousand yrs (preventing release back into the atmosphere
permafrosts cover 8% of land surface but hold half of the earths underground organic carbon
(!!Arctic tundra stores an estimated 180 billion tonnes of carbon!!)
THREATS: GLOBAL WARMING
rising temps risk ice melting which would release the thousands of years worth of carbon stored- outputs could eventually outweigh inputs
significance of different biomes: mangroves
- mangroves
more than 90% of total carbon in mangrove forests are stored in their soils.
globally mangroves are estimated to store over 6.4 billion tonnes of carbon (make up less than 2% of marine environment but store 10-15% of their carbon) store x10 more carbon per hectare than terrestrial forests!!!
THREATS: urban development could lead to further deforestation of mangroves releasing their stored carbon into the atmosphere
