Fast and slow carbon cycle

Fast carbon cycle:

This is the movement of carbon through food chains and takes place within a lifetime. Photosynthesis and the take-up of carbon dioxide from the atmosphere can just take a few minutes and within seconds the plant can be giving off carbon dioxide in respiration. It is estimated that the movement of carbon through food chains is up to 100,000 million metric tonnes a year.

Slow carbon cycle:

This cycle can take millions of years and involves the lithosphere store and the flow into the atmospheric store. Carbon is built up over millions of years in the laying down of sedimentary rocks and ocean sediments. This carbon dioxide is slowly released from marine deposits, the weathering of sedimentary rocks and transportation of rivers, or vented via volcanic activity. Its time scale us measured in 100s of thousands or millions of years.

Processes:

• mechanical, chemical and biological weathering of rocks on land
• decomposition of plants and animals
• transportation - rivers carry particles (ions) to the ocean where they are deposited
• sedimentation - over millennia, sediments accumulate, burying older sediments, e.g., limestone
• metamorphosis - the deep burial of sedimentary rocks combined with compression due to plate tectonics, sedimentary rocks turn into metamorphic, e.g., limestone to marble

Case Study:

Earth’s largest carbon store is the Himalayas.

• started as oceanic sediments rich in calcium carbonate
• carbon from the Himalayas is being actively weathered, eroded, and transported back to the ocean

<<80% of carbon-containing rock comes from shell-building organisms and plankton<<