p2 Flashcards
The Ocean as a Carbon Sink
The ocean’s are one of the Earth’s largest store, being 50 times greater than the atmosphere.
93% of CO2 is stored in undersea algae, plants and coral, with the remainder dissolved in the water.
Carbon cycle pumps are
processes operating within the oceans which circulate and store carbon.
There are three pumps you must be aware of: the biological pump, the carbonate pump and the physical pump.
Biological pump
This is the sequestration of C02 to oceans by phytoplankton. Phytoplankton float on the surface of the ocean to access sunlight and photosynthesise. They are autotrophs and are the base of the marine food web. Even though they are minute they make up over half the planets biomass.
Carbon is then passed up the food chain by consumers which in turn release C02 back to the atmosphere.
In this way most carbon is cycled in surface waters and only 0.1% reaches the sea floor through decompositions and sedimentation.
Phytoplankton sequester over 2 billion metric tonnes of C02 annually to the deep ocean.
Carbonate pump
- This relies on inorganic carbon sedimentation.
- Lots of marine organisms utilise calcium carbonate to make their outer shells/ skeletons.
- When these organisms die and sink to the sea floor many shells will dissolve on the way and the carbon will become part of the ocean and flow around the planet in currents.
- Shells that do not dissolve build up slowly on the sea floor forming limestone sediments such as those in the white cliffs of Dover.
Physical pump
This is the oceanic circulation of water including upwelling, down welling and the thermohaline current. C02 in the oceans is mixed much slower than in the atmosphere so there are large spatial differences in concentration.
Colder water can absorb more C02 so C02 concentration is 10% higher in the deep ocean than the surface and polar regions store more than tropical regions.
Warm waters release C02 into the atmosphere and cold waters absorb C02.
Large ocean currents like the North Atlantic Drift move water from the tropics to the poles, the water cools and absorbs more C02.
Physical pump current
The main current begins in polar oceans where the water gets very cold; sea ice forms; surrounding seawater gets saltier; increases in density and then sinks.
The current is recharged as it passes Antarctica by extra cold salty, dense water.
Division of the main current: northward into the Indian Ocean and into the western Pacific.
The two branches warm and rise as they travel northward, then loop back southward and westward.
The now-warmed surface waters continue circulating around the globe. On their eventual return to the North Atlantic, they cool and the cycle begins again.
The role of Phytoplankton
Phytoplankton float on the ocean’s surface to access sunlight and photosynthesise.
Despite their size they make up half of the planet’s biomass.
The absorb carbon, when eaten that carbon is passed along the food chain.
Part of that carbon is released through respiration.
Some carbon reaches the sea floor through decomposition and sedimentation.
Threatened by warming oceans.
Description of where phytoplankton found
Thrive along coastlines and continental shelves.
Found along the equator in the Pacific and Atlantic Oceans.
Thrive in high latitude areas.
why these areas?/
why these areas?/
Oceans rich in nutrients from deep water upwelling.
In high latitudes blooms peak in spring and summer when sunlight increases.
In subtropical oceans blooms decrease because surface waters warm up and become buoyant, with cold, dense water below the water not mixing easily, meaning nutrients are quickly used up.
Terrestrial (land-based) Sequestration
Terrestrial sequestration is the fastest part of the carbon cycle.
Globally, the most productive biomes are tropical forests, savannah and grasslands
the terrestrial sequestration process.
Primary producers (plants) take in carbon through photosynthesis and then release CO2 back into the atmosphere through respiration.
Consumer animals then eat these plants and absorb the carbon which becomes part of its fats and proteins.
Initially after the animal has died, microorganisms and detritus feeders such as beetles feed on waste material which becomes part of these micro-organisms.
After death, tissues decay into the soils. This process is affected by climate and decomposition will happen fastest in tropical climates (warm and damp) or, in Arctic biomes, the process can be ‘locked down’ for substantial time periods.
terrestrial carbon cycling fact
95% of a tree’s biomass (leaves, branches, trunk and roots) is made up from thee CO2 that it sequesters and converts into cellulose.
Carbon fixation
turns gaseous carbon into living organic compounds that grow.
Explain how carbon enters and exits the biosphere (4)
One way carbon enters the biosphere is through photosynthesis (1). Plants absorb and use atmospheric carbon which means that it enters the biosphere (1).
One way carbon can exit the biosphere is through animals (1). If an animal consumes the plant, then the carbon that the animal absorbs becomes part of their fat and protein which means that once that animal has died and decomposed the carbon will be released (1).
Other points: carbon enters microorganisms through decomposition, then respired.
Soils
- Soils store 20-30% of global carbon
- sequestering about twice the quantity of carbon as the atmosphere and three times that of terrestrial vegetation.
- Whether the soil sequesters or emits C02 depends on local conditions.
