How does carbon move between Earth's reservoirs and how do humans disrupt it?
Explain the carbon cycle reservoirs and fluxes and how human activity disrupts the balance
A focused answer to the WACE Year 12 Earth and Environmental Science dot point on the carbon cycle. Covers reservoirs, the fast and slow carbon cycles, fluxes such as photosynthesis, respiration and weathering, and how fossil fuel burning and land clearing disrupt the balance, with Australian context.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
SCSA wants you to describe where carbon is stored, the processes that move it, and how human activity unbalances the system. This cycle directly links Unit 3's resource focus to Unit 4's climate content, because excess atmospheric carbon dioxide drives the enhanced greenhouse effect.
Carbon reservoirs
A reservoir is a store of carbon. The major ones differ enormously in size and turnover time.
- Atmosphere: carbon dioxide and methane; small but climatically crucial.
- Oceans: the largest fast-exchanging reservoir, holding dissolved carbon dioxide and bicarbonate.
- Biosphere: living plants and animals.
- Soils: decaying organic matter and stored carbon.
- Geosphere: by far the largest store, locked in carbonate rocks and fossil fuels, but exchanging extremely slowly.
Carbon fluxes
A flux is a transfer of carbon between reservoirs.
- Photosynthesis removes carbon dioxide from the atmosphere and fixes it into plant tissue.
- Respiration and decomposition return carbon dioxide to the atmosphere.
- Ocean exchange moves carbon dioxide between air and sea, with cold water absorbing more.
- Weathering of rock slowly consumes carbon dioxide, while volcanism releases it.
- Burial of organic matter and carbonate locks carbon into the geosphere over geological time.
In a stable system these fluxes roughly balance, so reservoir sizes stay steady.
How humans disrupt the cycle
Human activity changes fluxes and shifts carbon between reservoirs.
- Burning fossil fuels transfers ancient geosphere carbon into the atmosphere within decades, far faster than it formed.
- Land clearing and deforestation release carbon stored in vegetation and soils, and remove a sink that would otherwise absorb carbon dioxide.
- The oceans and land vegetation absorb part of the extra carbon, acting as sinks, but cannot keep pace, so atmospheric carbon dioxide rises.
Ocean uptake of extra carbon dioxide also causes ocean acidification, a separate but linked impact on marine ecosystems such as coral reefs.