Carbon Cycle 1: System concepts

Question 1

What is the carbon cycle?

Answer 1

Biogeochemical cycle in which carbon moves from one part of the global store to another

Question 2

What kind of system is the carbon cycle at a global scale?

Answer 2

A closed system
The amount of carbon remains constant
There is a mass balance

Question 3

What kind of system is the carbon cycle on a local scale?

Answer 3

An open system
Mass balance is not constant
Balance changes as carbon enters or leaves the sub-system

Question 4

Carbon is one of the essential building blocks of what?

Answer 4

Organic life

Question 5

Carbon is essential due to its unique ability to form what?

Answer 5

Vital different bonds with other elements

Question 6

What kind of resource is carbon?

Answer 6

Finite

Question 7

Explain stores

Answer 7

Amounts of carbon held in the global system
e.g. atmosphere, oceans and biosphere, lithosphere

Question 8

Explain flows

Answer 8

Movements or transfers of carbon between stores
Volcanic activity adds 0.1 gigatons of carbon to the atmosphere annually

Question 9

What are flows i into stores called?

Answer 9

Inputs

Question 10

What are flows leaving stores called?

Answer 10

Outputs

Question 11

What is an example of the sequestration of carbon?

Answer 11

Photosynthesis

Question 12

What are the 4 processes of carbon pathways from land to the atmosphere?

Answer 12

Photosynthesis
Respiration
Decomposition
Fossil fuel combustion

Question 13

Explain the process of photosynthesis in carbon pathways

Answer 13

Carbohydrate molecules are produced from CO2 and water using energy from light. Plants ‘fix’ gaseous CO2 into solid form in their living tissues
Net Primary Productivity (NPP) of an ecosystem is the rate at which new organic matter is produced by photosynthesis per unit area per unit time

Question 14

Explain the process of respiration in carbon pathways

Answer 14

CO2 is released into the atmosphere by organisms by respiration. Plants create energy for respiration by breaking down stored glucose (sugars). CO2 is given off as a by-product

Question 15

Explain decomposition in carbon pathways

Answer 15

cO2 is returned to the atmosphere when living organisms die: their cells break down as a result of physical (wind and water), chemical (leaching and oxidation) and biological (feeding and digestion) mechanisms (carried out by bacteria and fungi

Question 16

Explain fossil fuel combustion in carbon pathways

Answer 16

Hydrocarbon (fossil fuel) combustion takes place rapidly in the presence of oxygen and releases CO2
Around 85% of global energy consumption is derived from coal, oil and gas fuels; traditional societies burn biomass on demand

Question 17

What are the two carbon pathways from the ocean to the atmosphere?

Answer 17

Physical pump
Biological pump

Question 18

Explain the physical (inorganic) pump

Answer 18

Movement of CO2 from atmosphere to ocean by diffusion
CO2 dissolved in the surface of the ocean can be transferred to the deep ocean in areas where cold dense surface waters sink
Downwelling carries carbon molecules to great depths where they may remain for centuries
CO2 diffusion determines the acidity of the oceans

Question 19

Explain the biological (organic) pump

Answer 19

Driven by ocean phytoplankton absorbing CO2 via photosynthesis
These organisms form the bottom of the marine food web and live in the oceans surface layer
Phytoplankton are consumed by other organisms and carbon is transferred along food chains
Organic carbon may eventually be transferred to the deep ocean when dead organisms sink towards the ocean floor

Question 20

What kind of form is carbon held in when in waters and the tissues of ocean dwelling organisms?

Answer 20

Dissolved form

Question 21

What are the primary inputs and outputs of carbon from the oceans?

Answer 21

Gas exchange with the atmosphere, but there is also significant input of both organic carbon and carbonate ions from continental runoff

Question 22

What is carbon flux within the oceans controlled by?

Answer 22

Physical, chemical and biological processes

Question 23

What kind of impact does small changes to the oceanic carbon store have?

Answer 23

Significant global impacts

Question 24

What proportion of carbon is eventually buried in ocean sediments?

Answer 24

Small proportion
But these sediments are important long term carbon stores

Question 25

Explain the four carbon pathways between the land and ocean (SLOW)

Answer 25

Between terrestrial bedrock and oceans occurs over millions of years
Rainwater containing weak carbonic acid reacts with limestone to produce soluble calcium bicarbonate
Calcium bicarbonate moves through the water cycle in solution into rivers and the ocean
Calcium bicarbonate is used by marine organisms to create shells; these are deposited later as carbonate-rich sediment on the ocean floor where they are lithified.

Question 26

Some carbon is eventually returned to the atmosphere by what? Explain this.

Answer 26

Volcanism
When CO2 is released from melted rocks when subduction occurs at plate boundaries