What is the difference between a carbon sink and reservoir？

[Kior]

I am trying to figure out the difference between a carbon sink and a carbon reservoir. The definition for a carbon sink from wikipedia is that “carbon sinkis a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. ” And the definition for carbon reservoir is “ Carbon-storing natural feature (such as a forest or the land mass) that exchanges carbon with other reservoirs." My textbook says that mature forests are carbon reservoirs but they are not carbon sinks. So what is the difference between a carbon sink and a carbon reservoir on earth?

 

[SteamKing]

A "carbon sink" is a semi-colloquial term, IMO.

As to the ability of a carbon sink or a carbon reservoir to store carbon, there is no functional difference.

 

[Astronuc]

I believe the term 'sink' refers to a dynamic form in which some form of mass/energy transfer is ongoing.

The term reservoir would be more or less static, e.g., an oil deposit/reservoir or coal formation, that does not change over a long period of time.

 

[Ophiolite]

Astronuc, I believe you have the correct distinction, but have applied it incorrectly. My understanding - and this is reinforced by the the definitions Kior offered in the OP - is that a sink will remove carbon from the action for an extended period of time. So the coal or oil that you mentioned would be carbon sinks, as would limestones. The derivation, I suspect, is that the carbon metaphorically sinks out of sight for an extended time.

In contrast carbon stored in a reservoir such as a forest is continually recycled as vegetation dies, then rots.

Steam King's point about them being identical may be a reflection of careless usage.

 

[Baluncore]

When modeling a natural system you can only study a limited part of reality.

Where material enters your model, it appears from a “source” at some specified rate.
Where material exits your model, it disappears into a “sink” at some specified rate.

A “reservoir” has inputs and outputs. Material is held temporarily in a “reservoir” and tracked as a state variable that specifies the amount of material in the reservoir.

So the meaning of sink and reservoir will depend on the scope of your model.