Biogeochemical Cycles
Mrs. Ashley
Carbon Cycle
\There is estimated to be over 5 x 1022g of carbon on earth. One tonne is 106g, so this is 5 x 1016 tonnes, or to put it
another way:
50,000,000,000,000,000 tonnes of carbon on earth
About 99% of this is locked away in sedimentary rocks such as limestone and chalk (both of these are made of
calcium carbonate CaCO3), the remainder can pass through the various carbon sinks and reservoirs as part of the
carbon cycle and so is in some manner "available". This remaining carbon is distributed between a number of
reservoirs, some living - for instance you represent a carbon reservoir approximately equivalent in size to a small
bag of barbeque charcoal. Some is atmospheric, some is dissolved in water and some is buried beneath the earth.
Carbon reservoir
Mass in tonnes of carbon x 109
(billions of tonnes of carbon)
% of total
Atmosphere
740.0
1.43
Land plants
550.0
1.06
Land animals
0.5
0.001
Marine plants (algae)
1.5
0.003
Marine animals
1.5
0.003
Dead organic matter (in soil and peat)
1600.0
3.08
Coal
4500.0
8.67
500.0
0.96
38 000.0
73.2
6000.0
11.6
Oil and gas
Dissolved in the oceans
Marine sediments
Totals
51 893.5
100.007
This distribution is often rather surprising at first sight, notably because there is so much carbon dioxide
contained dissolved in the oceans and relatively little is contained in the atmosphere. The atmosphere however is
exceptionally important in that it is the transfer medium between the other sinks and while relatively little stays in
the atmosphere a great deal passes through it.
The oceans are by far the largest sink of carbon as dissolved carbon dioxide. This is medium-term storage and is in a
balance with atmospheric carbon dioxide, if atmospheric carbon dioxide is removed, it will replaced by some that
was dissolved in the oceans, if large amounts of carbon dioxide are released into the atmosphere, much of it will be
absorbed by the oceans. The vast majority of carbon dioxide released since the start of the industrial revolution is
now held dissolved in the worlds oceans if this was not the case, the atmospheric levels would have risen far more
than they even have.