1.c. The carbon cycles have distinctive processes and pathways that operate within them

Question 1

Processes of the carbon cycle- precipitation

Answer 1

• atmospheric CO2 dissolves in rainwater to form weak carbonic acid
• rising conentrations of CO2 in atmosphere, due to anthropogenic emissions, have increased the acidity of rainfall which has increased the acidity of ocean surfaces, harming marine life

Question 2

Processes of the carbon cycle- photosynthesis

Answer 2

• the flux of carbon form the atmosphere to land plants and ocean phytoplankton through photosynethsis averages around 120 GT a year
• light energy is converted to chemical energy through this process

Question 3

Processes of the carbon cycle- weathering

Answer 3

• the breakdown of rocks on/near the earth’s surface by physical, chemical and biological processes
• acidic rainwater will slowly dissolve limestone and chalk through carbonation- this releases additional carbon into rivers oceans and atmosphere which is most effective beneath soil as there is a higher CO2 concentration

Question 4

Processes of the carbon cycle- chemical, physical, biological weathering

Answer 4

• chemical weathering transfers an estimated 0.3 billion tonnes of carbon to atmosphere and oceans each year
• physical weathering breaks rock down through processes like freeze thaw weathering, exposing a greater surface area to chemical weathering
• biological weathering processes like chelation are effective in warm, humid climates

Question 5

Processes of the carbon cycle- respiration

Answer 5

• this is where carbohydrates are converted to CO2 and water
• it is the reverse of photosynethesis as oxygen is absorbed and CO2 is released
• respiration and photosynethsis are the most important processes in the fast carbon cycle because of the sheer volume exchange

Question 6

Processes of the carbon cycle- decomposition

Answer 6

• bacteria and fungi breakdown organic matter, extracting energy and releasing CO2 to the atmosphere
• rates of decomposition are dependent on climate
• warm humid climates increase rates of decomposition whilst dry/cold climates slow rate

Question 7

Processes of the carbon cycle- combustion

Answer 7

• this is when organic material burns in the presence of oxygen, releasing CO2 and other gases
• wildfires caused by lightening strikes speed up carbon cycle in places where decomposition is slow. Also clear the forest canopy, increasing biodiversity
• results from human activity e.g. clearing land for cultivation
• despite attempts to curb CO2 emisssions, consumption continues to grow- it transfers 10GT of CO2 a year from geological stores to atmosphere, oceans, biosphere

Question 8

Processes of the carbon cycle- carbon sequesration (long term storage of carbon dioxide)- physical pump

Answer 8

• the physical pump involves mixing of sueface and deep water ocean waters by vertical currents, creating a more even ditribution of carb
• CO2 enters oceans from atmosphere by diffusion. Surface ocean currents transport water and its dissolved CO2 polewards where it cools, becomes more dense and sinks
• downwelling carries dissolved carbon to ocean depths where individual carbon molecules may remain for centruies
• eventually deep ocean currents transport carbon to areas of upwelling. There cold carbon rich water rises to surface and CO2 diffuses in atmosphere

Question 9

Processes of the carbon cycle- carbon sequesration (long term storage of carbon dioxide)- biological pump

Answer 9

• action of marine organisms
• phytoplankton combine sunlight, water and dissolved CO2 to produce organic material
• whether consumed by animals in marine food chain or through nature death, carbon locked in the phytoplankton either accumulate in sediments on the ocean floor or is decomposed and released into ocean as CO2
• other marine organisms such as molluscs extract carbonate and calcium ions from sea water to manufacture plates, shells and skeletons of calcium carbonate. Eventually this is lithified to form chalk and limestone

Question 10

Processes of the carbon cycle- carbon sequesration (long term storage of carbon dioxide)- vegetation

Answer 10

• land plants e.g. trees in ranforests contain huge stores of carbon
• most of this is extracted from atmospheric CO2 through photosynthesis and is locked away for decades