The Carbon Cycle

Question 1

Why is knoledge about the carbon cukle important?

Answer 1

• It is essetial to understand climate change.

Question 2

Rough approximation of carbon reservoirs:

Answer 2

• Land 2000 - 4000 (?) [Pg]
• Ocean 40 000
  ( - Rock (magma) 1 200 000
• Fossil fuels 5000 - 10 000
• Atm. ca 840 today (?) annual increase 6 Pg

Question 3

Approximate Carbon fluxes (to and from atm):

Answer 3

• Land 120 +-
• Ocean 80 +-
• Rocks 0.4 +-
• Fossil fuels 10 + !

Question 4

CO2 concentration in atmosphere

Answer 4

• 410 ppm
• current increase of 2 ppm/year
• Has stayed quite steady bellow 400 ppm for millions of years before.

Question 5

Flux from volcanic activity and weathering:

Answer 5

• 0.1 +- Pg C/year

Question 6

What is the net effect from volcanic feedback and what is the response time?

Answer 6

• negative feedback to temperature

- tau_cycle = 100 000 of years

Question 7

Ocean warming net effect:

Answer 7

• positive feedback to temperature.
  The ocean take up atmosphereic heat, but the warmer it gets the less CO2 goes there from the atmosphere.
  (The higher the revelle-factor gets)

Question 8

Qualitative effect from ocean carbon pumps:

Answer 8

• Carbon is slowely transported to the deep ocean
  (one pump pumps it down and the other pumps it up, via photosytheses and shellbuilding respectively. Some dead biota sinks.)

Question 9

What is the sauration state for the pumps?

Answer 9

(dissolves, omega<1

Question 10

Why is Ocean carbon reservoir so complex?

Answer 10

• Many parts of the ocean carbon mechanisms are well understod, like most chemical reactions and temperature influence on CO2 solubility.
• The ocean circulation are vary complex and less understod.
• The ocean is stabilizing the carbon system by absorbing CO2, but we dont fulle understand what will happen in the future.

Question 11

Most stable forms of C on Earth:

Answer 11

Oxidized

• CO2
• CO3(2-)

Question 12

How is CO2 broken down?

Answer 12

• Most of the CO2 is not broken down at all, only transported around the different reservoirs
• Photosynthesis stores solar energy by reducing CO2 to organic carbon (Uses exergy from sun to create chemical disequilibria. Essential for life on Earth.)

Question 13

What other carbon reservoir has most impact on the atmospheric carbon reservoir?

Answer 13

• The Ocean is the largest carbon reservoir and greatly influences atmospheric CO2 levels on 10- 10 000 of years, through many different mechanisms.

Question 14

Why is it easy to create CO2 and hard to create CH4?

Answer 14

• CH2O is organic C and has oxidation state 0
• C in CO2 has oxidation state (+4)
• C in CH4 has oxidation state (-4) and contains stored energy that may be relised by oxidation. Energy demanding to create.
• Higher oxidation numbers are thermodynamically more stable. (Closer to chemical equilibrium)

Question 15

Explain:

• GPP Gross Primary Production
• NPP Net Primary production
• NEP Net Ecosystem Production

Answer 15

• Total energy assimilated in photosynthesis
• Total energy in plant mass production
• Total energy in accumulating (mainly dead) organic matter
  (Energy for CO2 land fluxes)

Question 16

How is cellulose broken down?

Answer 16

• Only microbes posses the enzyme cellulase needed for breaking down celulose into its suger components.
  (- These microbes also exists in cows.)

Question 17

3 different forms of living carbon:

Answer 17

• Carbohydrates (cellulose)
• Proteins
• Lipids

Question 18

Largest vegitation carbon reservoir?

Answer 18

• Peatland (torvmark)

Question 19

When you have all the rain you need for forestation, what is the main factor that determines forest or no forest?

Answer 19

Fires

Question 20

What determines plant carbon densities?

Answer 20

• Temperature
• Sunlight
• Water
• Nutrients
• Atmospheric CO2 levels
  ( and even if trees grow more quickly, they might not become larger)

Question 21

What is the risks og climate change and desforestation?

Answer 21

• Forest areas might become permanent grasslands. Binds much less carbon than forests.

Question 22

Why is there stil reduced carbon in peatland soils and permafrost soils?

Answer 22

• Peatland: Low oxegyn concentration

- Permafrost: Low temperature

Question 23

How can reduced soil carbon exist?

Answer 23

• Soil carbon is degradable by microbes and enzymes.

- It is the lack of accesability of soil C for the microbes and enzymes that stabilizes soil C over long time.

Question 24

Why does peatlands store carbon?

Answer 24

• Plant litter production outpaces decay
• slow O2 diffusion in water, slow decay
• The stored carbon is protected as long as the peat remains waterlogged (wetland).

Question 25

What is the most reduced and energy rich form of carbon?

Answer 25

CH4 - Methane

Question 26

How is Methane contributing to climate change?

Answer 26

- GHG - 100 times stronger than CO2 /kg - Residence time in atm. ca 10 years - 2'nd most contributing to Global Warming, after CO2

Question 27

How is CH4 produced?

Answer 27

- oxygen-free conditions, by anarobic bacteria and fungi - Inside Earth by high pressure and temp. - Incomplete oxidation in combustion (- does only occur when low concentration of other electon acceptors, SO4(2-), NO3(1-). Seawater has high SO4(2-) )

Question 28

Why is CH4 produced by ruminants (cows)?

Answer 28

- They have an organ called rumen that hosts the fermentative and methanogenetic microbes, who can break down cellulose, and therefore cows can manage by just eating grass.

Question 29

How much of land carbon do we find in dead organic matter in soils, including peatland and permafrost?

Answer 29

80%

Question 30

Where are more than 80% of the living land carbon?

Answer 30

In forests

Question 31

How many domestic ruminants do we have in the world today?

Answer 31

3.9 billions ( humans = 7.6 billions )

Question 32

The ocean CO2 uptake cycle, chemical formulas:

Answer 32

- CO2(gas) CO2(aqueous) 1 year - CO2+H2O+CO3(2-) 2(HCO3(1-)) 10-1000 years - CaCO3+CO2+H2O Ca(2+)+2(HCO3(1-)) 1000-10 000 years

Question 33

Examples of a few feedbacks for for land C cycle to atmospheric CO2:

Answer 33

- Photosyntesis (-) - Temp (mostly +) - Rainfall - More grassland - Respiration etc

Question 34

Time before significant permafrost loss:

Answer 34

- 100-1000 years | - slow feedback

Question 35

Main underlying drivers of C emissions:

Answer 35

- food - housing - travel (fastest increase)

Question 36

Main sorces for CO2 emissions?

Answer 36

- Fossil energy use is the main cause of CO2 emissions. | - Land has been a large net sourse (acumulated though time) from deforestation to food production.

Question 37

How much higer are CO2 and CH4 concentratiosn now looking back a million years.

Answer 37

- CO2 about 30% higher | - CH4 about 300% (3 times) higher

Question 38

How much of the CO2 emissions has and will the ocean absorb?

Answer 38

- The ocean has absorbed about 30% of teh emissions since 1750, and will most likely absorb about 50% in the long run. - Most of the mechanisms of ocean uptake are known with medium or high confidence.

Question 39

How will the land c cykle respond to future CO2 emissions?

Answer 39

- The plats will probably be a net sink. - The soil will probably be a net source. - The over all responce (feedback) is very uncertain.