Geoscience Reference
In-Depth Information
(A)
Fossil fuels
5000
Atmosphere
600
Biosph+Soils
2000
Surface ocean
1000
10−100 yr
Deep ocean
37 000
100−1000 yr
Sediments
5000
1000−100 000 yr
(B)
> 100 000 yr
C
org
oxidation
Volcanism
Atmosphere
Biosphere
Ocean
~40 000 Pg C
Carb/Silicate
weathering
Carbonate
burial
C
org
burial
Long-term (rock) reservoir
~10
8
Pg C
Figure 2.1
(A) The surface (exogenic) carbon cycle. Approximate reservoir sizes are in units of Pg C (1 Pg = 10
15
g). The dashed boxes demarcate
reservoirs involved in carbon exchange on the respective timescales. (B) The long-term carbon cycle.
the evolution of the carbonate system in seawater
(for carbon cycling, see Fig. 2.1). The characteriza-
tion of the dominant carbon and total alkalinity
l uxes to and from the oceans on different timescales
is hence fundamental to understanding controls on
ocean CO
2
chemistry (e.g. Sundquist 1986 ).
surface include the atmosphere (pre-anthropogenic
inventory ~600 Pg C; 1 Pg = 10
15
g), the biosphere
(~500 Pg C), soils (~1500 Pg C), and the surface
ocean (~1000 Pg C). Combined, these reservoirs
hold less than ~4000 Pg C (see Fig. 2.1A). Fossil fuel
reserves, on the other hand, have been estimated at
~5000 Pg C (excluding hydrates). It is thus immedi-
ately clear that the release of several thousands of
Pg C over a few hundred years will overwhelm the
capacity of these surface reservoirs to absorb
carbon.
2.3.1
Decadal to centennial timescale
On timescales shorter than about 100 years, the nat-
ural reservoirs that exchange carbon at the earth's
