Carbon Cycle Pack B

Question 1

How does the fast carbon cycle work?

Answer 1

• Carbon is cycled rapidly between the atmosphere, ocean, soils and living organisms
• Surface of the ocean absorbs carbon dioxide via diffusion but also loses some
• Phytoplankton use dissolved CO2 in the surface ocean for photosynthesis (and to build their cells) and release it back in respiration
• Trees absorb CO2 for photosynthesis and release it during respiration
• Carbon gets passed down food chains from plants to animals and humans
• Animals/humans release CO2 to the atmosphere via respiration
• Fungi and bacteria break down dead organisms/matter via decomposition, which releases CO2 to the atmosphere as they respire
• Some carbon compounds recycle into the soil

Question 2

How does the slow carbon cycle work?

Answer 2

• Carbon diffuses from the atmosphere to the surface ocean
• Marine organisms fix dissolved carbon with calcium to create shells and skeletons (CaCO3)
• When they die, their remains sink to the bottom of the ocean, accumulate over thousands/millions of years and heat/pressure convert them into carbon-rich sedimentary rocks
• Carbon in rocks is released as CO2 during volcanic eruptions
• Some sedimentary rocks are moved and subducted at plate boundaries and partially melted
• Some are ejected and attacked by chemical weathering (carbonic acid) or uplifted and exposed
• CO2 released is dissolved in rain water (acid rain) or ends up in streams/rivers

Question 3

How long does the slow carbon cycle take?

Answer 3

100-200 million years

Question 4

How many tonnes of carbon is circulated in both cycles?

Answer 4

Fast cycle = 1000 - 100000 million tonnes a year
Slow cycle = 10 - 100 million tonnes a year

Question 5

How many tonnes do humans release per year?

Answer 5

43 billion tonnes