Unit 3.1 - W&C - The Global Carbon Cycle Flashcards
What is the carbon cycle?
The carbon cycle is a core physical geography topic. The cycle has several main components:
Stores (amounts of carbon held by different parts of the global system e.g. the atmosphere, oceans and biosphere)
Flows (movements or transfers of carbon between stores e.g. volcanic activity adds 0.1 gigatonnes of carbon to the atmosphere annually)
Inputs (flows into stores e.g. carbon dioxide added to the atmosphere by human activities)
Outputs (flows leaving stores e.g. dissolved carbon carried from the land by rivers).
Define the abbreviation GtC.
GtC demotes one gigaton of carbon dioxide equivalent.
One gigaton (GtC) equals one billion tonnes (or one trillion kg).
Outline the major and minor carbon stores.
Sedimentary (carbonate) rocks and deep ocean sediments are by far the largest carbon store, holding 100,000,000 GtC.
In contrast, the two smallest stores are Earth’s atmosphere and biosphere (ecosystems). They held 600GtC and 560 GtC respectively at the start of the industrial revolution.
Outline the key physical processes in the carbon cycle.
Photosynthesis
Respiration
Decomposition
NPP
What is photosynthesis?
In photosynthesis, carbohydrate molecules are produced from CO2 and water using energy from light. Plants ‘fix’ gaseous CO2 into solid form in
their living tissues.
What is NPP?
The net primary productivity of an ecosystem is the rate at which new organic matter is produced by photosynthesis per unit area per unit time.
What is respiration?
CO2 is released into the atmosphere by organisms through the process of respiration. Plants create energy for this process by breaking down stored glucose (sugars). CO is given off as a by-product.
What is decomposition?
CO2 is returned to the atmosphere when living organisms die: their cells break down as a result of chemical (leaching and oxidation) and biological (feeding) processes linked with bacteria and fungi. This is decomposition.
Give examples on how carbon processes can vary from place to place.
The three global environments with the highest rates of net primary productivity (NPP) are, in order, shallow warm-water estuaries, marshes and tropical rainforests. Rates of decomposition vary greatly too. In humid locations with warm all-year-round temperatures, such as tropical rainforests, dead plants and animals can decompose beyond recognition within days. In contrast, decomposition occurs so slowly in the Arctic tundra that recognizable plant and animal remains may lie on the surface of the ground for many months, or even years.
Describe how carbon pathways and processes between oceans and the atmosphere affect the carbon cycle.
The physical (inorganic) pump involves movement of CO2 from the atmosphere to the ocean by the process of diffusion. CO2 dissolved in ocean surface waters can be transferred to the deep ocean in places where cold, dense surface waters sink. This downwelling carries carbon molecules to great depths where they may remain for centuries.
The biological (organic) pump is driven by ocean organisms called phytoplankton, which absorb CO2 via photosynthesis. These organisms live in the ocean’s surface layer and are consumed by other organisms in marine. Organic carbon may eventually be transferred to the deep ocean when dead organisms sink towards the ocean floor where their remains create sediments.
How does chemical weathering and river transport of material transport carbon over time?
Rainwater contains weak carbonic acid which reacts with limestone to produce soluble calcium bicarbonate. Next, calcium bicarbonate moves through the water cycle in solution into rivers and then the ocean. Calcium bicarbonate is used by marine organisms to create shells; these are deposited later as carbonate-rich sediment on the ocean floor. Some carbon is returned to the atmosphere by volcanism, when CO is released from melted sediments and rocks when subduction occurs at plate boundaries. This process may take millions of years to complete
