2.2 The carbon cycle

Exam style question: Explain the importance of fluxes to the carbon cycle (6 marks)

What are stores of carbon also referred to as?

Pools, stocks and reservoirs

What are the three types of carbon store?

Terrestrial, oceanic and atmospheric

What is flux?

The movement or transfer of carbon between stores. It creates cycles and feedbacks

What is the ‘slow carbon cycle’?

The geological carbon cycle, which is slow and involves a number of chemical reactions that create new stores which trap carbon for significant periods of time.

What is terrestrial carbon?

Carbon held within the mantle, which is released into the atmosphere as carbon dioxide when volcanoes erupt in a process called ‘out-gassing’

What happens when CO₂ in the atmosphere combines with rainfall?

It produces a weak carbonic acid that dissolves carbon-rich rocks, releasing bicarbonates

How do rivers contribute to the carbon cycle?

They transport weathered carbon and calcium sediments to the oceans, where they are deposited

What builds up strata of coal, chalk and limestone?

Carbon in organic matter from plants and from shells and skeletons sinks to the ocean bed when they die, which builds up over time

How does the subduction of carbon-rich rocks contribute to the carbon cycle?

The carbon eventually emerges again as CO₂ when the volcano erupts

How does the metamorphosis of rocks contribute to the carbon cycle?

The presence of intense heating along subduction plate boundaries metamorphoses the sedimentary rocks, releasing CO₂

What are the roles of living organisms in maintaining the efficient running of the bio-geochemical carbon cycle?

• photosynthesis

• respiration

• decomposition

• combustion

How much carbon is estimated to have been added to the atmosphere as a result of burning fossil fuels?

180 gigatonnes (Gt), which is enough to alter the concentration of greenhouse gases in the atmosphere and trigger climate change

What are the three forms of carbon?

• inorganic

• organic

• gaseous

What is the quickest carbon cycle process?

Plants taking carbon from the atmosphere through photosynthesis, and then releasing it by respiration. It is controlled by temperature and moisture

What is the slowest carbon cycle?

Dead organic material in soils may retain carbon for years or centuries. Some may not decay at all and transform into sedimentary rocks.

How can CO₂ fluxes vary globally?

Latitude, with levels always higher in the Northern Hemisphere, as it contains greater landmasses and has greater temperature variations