Three

THE CARBON CYCLE – FEEDBACK LOOP :) 21/01/2010

Hi 04 =]] Let’s summarize what we’ve learnt for today! YAY!

Feedback loop: a mechanism/process/signal that is looped back to control a system within itself.

*Negative feedback: help to maintain stability in a system.

Ex: in a jungle, snakes eat rabbits.

The number of rabbits increase

-> the number of snakes increase, but then when snakes increase in number, snakes eat more rabbits

-> the number of rabbits decreases

->snakes do not have enough rabbits to eat

->snakes die and the number of snakes decrease

->the number of rabbits increase again :)

(So you can see that it goes around and around and maintain the stability of the system)

Positive feedback: is when part of output is fed back to increase the input. It’s unstable.

Ex: Abe do = flexibility of the surface.

Ex: On snowy regions (like mountains or North pole, etc.).

If the earth is warmer due to global warming, those regions will become warmer, land will absorb more heat and become even hotter.

Four major Carbon reservoirs

- Organic molecules in living/dead organisms found in biosphere

- As CO2 in atmosphere

-As fossil fuel & sedimentary rocks & organic matter in soil in lithosphere

-As dissolved CO2 in oceans

Carbon cycle is regulated by feedback loops

Amount taken up through photosynthesis ≈ the amount emitted through respiration and decomposition.

Flow of Carbon in fossil fuel≈ 0

Some processes of Carbon Cycle

-Photosynthesis

-Respiration

-Diffusion

-Subduction

-Deposition

etc.

A negative feedback Loop in the Carbon Cycle

Carbon flows from atmosphere -->ocean and vice versa.

These 2 flows are approx. equal because of the diffusion of Carbon from atmosphere to the storage

--> equilibrium between the amount of carbon in the atmosphere and ocean.

However, Combustion + deforestation disrupt this equilibrium

--> Add carbon to atmosphere

--> [C] in atmosphere > [C] in ocean

--> Carbon then diffuses from atmosphere to ocean

REVELLE FACTOR: Negative feedback loop limits the size of the flow

--> CO2 dissolves in ocean, it reduces the ocean’s pH

--> ocean more acidic

--> Slows down the rate at which CO2 dissolves in the ocean

Positive feedback Loop in Carbon Cycle

Permafrost in Siberia

Contains peach, carbon-rich organic material and methane

And finally, homework!!!

From the passage look for a possible suggestion to explain the mystery of the missing Carbon

Is there a negative feedback loop

Explain why (seemingly) negative feedback loop may actually work as a positive feedback loop in Carbon Cycle?

(Note: Ms Lo said that the answer is maximum half a page, as in you can just have 1 word for your answer =)) not to write a super long long essay or anything=)) ) Ok! Have fun studying

I think today's lesson is easy to understand and it's interesting to see how Feedback loop regulates the amount of carbon around us =)) but i dont know why they call "negative feedback" when it makes the system stable, and "positive feedback" when it's unstable?

oh, i have a question ( maybe we've learnt this before but i forgot =(( ): what's carbon footprint? (when we played the word guessing game)

Giang =]]