Lectures 9 & 10: The Carbon Cycle

Question 1

Why is carbon essential for life?

Answer 1

• Central element of organic compounds
• Involved in energy acquisition & use
• Maintains long term stability in global climate

Question 2

What is the carbon cycle?

Answer 2

The movement of carbon through abiotic and biotic reservoirs

Question 3

What is a source vs a sink?

Answer 3

Source = reservoir that releases more carbon than it received
sink = reservoir that receives more carbon that it releases

Question 4

What is a Gt

Answer 4

1 Gigatonne = 1 billion tonnes
1 Gt carbon = 3.22 Gt CO2

Question 5

What is the inorganic carbon cycle?

Answer 5

cycling of carbon between rocks, oceans, and the atmosphere

Question 6

What are the reservoirs and linkages of the inorganic carbon cycle?

Answer 6

Reservoirs: oceans, atmospheres, rocks

Linkages: precipitation, chemical weathering, solubility pump, deposition, volcanism, mountain-building.

Question 7

How does precipitation affect the inorganic carbon cycle?

Answer 7

CO2 in the atmosphere reacts with water vapour to form carbonic acid, which causes slightly acidic rain to fall and moved this carbon into ocean reservoirs.

Question 8

How does chemical weathering affect the inorganic carbon cycle?

Answer 8

Acidic precipitation forms and reacts with sedimentary rocks: calcium and bicarbonate ions are released, which eventually wash away into the ocean.

Question 9

What is the solubility pump?

Answer 9

the exchange of carbon between the atmosphere and the ocean:
- CO2 dissolves at the surface of the ocean releasing carbonic acid, bicarbonate ions, carbonate ions, and hydrogen ions.

Question 10

What happens to the ions brought into the ocean via the inorganic carbon cycle?

Answer 10

Deposition: the ions combine in solution to form calcium carbonate (also formed by shell-producing marine life forms), which then collects at the ocean floors and forms mineral deposits like carbonate rocks.

Question 11

What is volcanism?

Answer 11

Melting rocks due to intense heat and subduction of tectonic plates emerge into the atmosphere.

Question 12

What is subduction?

Answer 12

When one tectonic plate is pushed under another as the two are forced together. An ocean plate (with CaCO3 deposits) is often forced to subduct (be pushed under).

Question 13

How does volcanism affect the carbon cycle?

Answer 13

The chemical composition of the melting carbonate rocks releases CO2 during the breakdown. It also produces new rock which becomes exposed to the surface and weathers, releasing tons more minerals each time.
Infrequent but regular.

Question 14

What is a mountain-building event?

Answer 14

the formation of elevated regions or rock (often not previously exposed).

Question 15

How does mountain-building affect the carbon cycle?

Answer 15

Whether through tectonic plate shifts or as a result of volcanism, the newly exposed carbon on the mountains is exposed to chemical weathering.

Question 16

How does location of mountains affect their effect on the carbon cycle?

Answer 16

Mountains in the equatorial region experience more rain and therefore more weathering.

Question 17

What are linkages within the organic carbon cycle?

Answer 17

• photosynthesis
• decomposition
• cellular respiration
• combustion
• biological pump

Question 18

how does photosynthesis affect the carbon cycle?

Answer 18

Removes atmospheric carbon dioxide and converts it into sugar (fixed carbon) used by other life forms (for energy or as structural support)

Question 19

How does cellular respiration affect the carbon cycle?

Answer 19

All aerobic life fuel cellular respiration with sugars produced by primary producers, and releases gaseous CO2 as a waste product.

Question 20

How does decomposition affect the carbon cycle?

Answer 20

complex organic molecules containing carbon get broken down into simpler compounds and deposits into the soil as humus.

Question 21

How do fossil fuels form?

Answer 21

Dead organic matter is buried by sediments before it can decompose and this weight (compression) pushes it deeper into the earth (hotter) and transforms the large carbon molecules into small oil and coal molecules.

Question 22

How does combustion affect the carbon cycle?

Answer 22

Forest fires balance carbon lost to combustion with carbon sequestered by photosynthesis.

Question 23

How does ocean life affect the carbon cycle?

Answer 23

Shell-forming marine life builds calcium carbonate, which build up as thick mineral deposits.

Question 24

How does carbon move between shallow and deep waters in the ocean?

Answer 24

natural upwelling and downwelling of dissolved CO2, and movement of organisms moves carbon between surface and deep waters.

Question 25

How do seasonal fluctuations affect the carbon cycle?

Answer 25

spring/summer: plant life grows and photosynthesis increases (intake of CO2)
Fall/winter: plant life growth slows and stops, in which decomposition of leaves and cellular respiration become the primary CO2 processes.

Question 26

What is the human induced carbon cycle?

Answer 26

• Burning fossil fuels
• Changing land use (removing vegetation and modifying existing rates of organic carbon cycling)
• creating concrete from limestone

Question 27

What is ocean acidification? How does it affect marine life?

Answer 27

Increasing acidity in the ocean (due to increased CO2 in the atmosphere) affects all marine plant and animal life. Increased H+ ions bind with negative carbonate/bicarbonate ions. This removes the dissolved carbonate and prevents shells and coral from growing thicker.

Question 28

What is the greening hypothesis?

Answer 28

That increased atmospheric CO2 enhances plant growth, which in turn boosts photosynthesis to regulate the amount of CO2 in the atmosphere (negative feedback loop).

Question 29

Why was the greening hypothesis wrong?

Answer 29

Because greenhouse conditions are not representative of real world conditions: there are other limiting resources (such as minerals, etc…) that limit plant growth even with unlimited CO2.