4. Carbon Cycle

Question 1

What does air monitoring stations do?

Answer 1

measure concentrations of carbon dioxide, methane and other gases

Question 2

What do carbon dioxide concentrations show annually?

Answer 2

fluctuation:

• drop: May - October
• rise: October - May

Question 3

Explain why carbon dioxide levels show an annual fluctuation?

Answer 3

drop: excess of photosynthesis over cell respiration globally
rise: excess of cell respiration of photosynthesis globally

changes follow northern hemisphere seasons because:

• area of lang is greater in northern hemisphere
• and carbon dioxide concentrations are greater on land than in sea

Question 4

Apart from annual fluctuations in carbon dioxide concentrations, what other trends are there?

Answer 4

rising trend in atmospheric carbon dioxide concentrations due to human activities

Question 5

Is it possible to measure global carbon fluxes precisely?

Answer 5

no, but scientists have produced estimates based on many measurements in natural ecosystems and in mesocosms

Question 6

What are global fluxes of carbon measured in?

Answer 6

gigatonnes

Question 7

Name the 6 process that make a significant difference to global atmospheric carbon dioxide levels each year.

Answer 7

1 photosynthesis
2 cell respiration
3 ocean uptake
4 ocean loss
5 deforestation and land use changes
6 combustion of fossil fuels

ocean uptake = CO2 from atmosphere dissolving in water

Question 8

What is the flux produced by photosynthesis in gigatonnes per year?

Answer 8

-120 (minus 120, photosynthesis takes 120 gigatonnes of carbon dioxide out of the atmosphere per year)

Question 9

What is the flux produced by cell respiration in gigatonnes per year?

Answer 9

+119.6

Question 10

What is the flux produced by ocean uptake in gigatonnes per year?

Answer 10

-92.2

Question 11

What is the flux produced by ocean loss in gigatonnes per year?

Answer 11

+90.6

Question 12

What is the flux produced by deforestation and land use changes in gigatonnes per year?

Answer 12

+1.6

Question 13

What is the flux produced by combustion of fossil fuels in gigatonnes per year?

Answer 13

+6.4

Question 14

What does limestone mainly consist of?

Answer 14

calcium carbonate (CaCO3)

Question 15

What can limestone rock often contain?

Answer 15

fossils such as mollusc shells and skeletons of hard coral

Question 16

What is significant about fossilised organisms such as mollusc shells and skeletons of hard coral?

Answer 16

• they abosorb calcium and carbonate ions and secrete them as calcium carbonate:
• marine molluscs die > the shells fall to the sea bed > becomes part of limestone rock > skeletons of hard corals accumulate over time > gradually builds a coral reef (which consists of limestone)

Question 17

“Huge amounts of …. are locked up in limestone.” Fill in blanks.

Answer 17

carbon

Question 18

How can carbon in limestone be released?

Answer 18

if the limestone reacts with acid

Question 19

How can rainwater cause limestone to break down?

Answer 19

• rainwater contains carbonic acid (H2CO3)
• acid breaks down limestone

carbonic acid + calcium carbonate –> calcium ions + hyrdogen carbonate ions

Question 20

Name the 2 types of fossil fuel formation.

Answer 20

1 peat and coal

2 oil and gas

Question 21

How are fossil fuels formed with peat and coal?

Answer 21

• saprotrophs cannot break down organic matter in acidic and anaerobic conditions
• these conditions are found in bogs and swamps
• partially decomposed plant matter accumulates to form thick deposits called peat
• in past geological eras, peat was crushed to form coal

Question 22

How are fossil fuels formed with oil and gas?

Answer 22

• silt deposited on bed of some shallow seas
• mixes with remains of dead organisms
• organic matter only partially decomposed because of anaerobic conditions
• this process occurred in past geological areas
• silt converted to shale, with compounds from organic matter becoming oil or gas trapped in pores in rock