Chemistry Reference
In-Depth Information
FIGURE 18.2
A generalised biosphere model showing the basic inputs and outputs of energy and materials. Geochemical (abiotic) trans-
formations are represented at the top (atmospheric) and bottom (tectonic and geothermal) compartments, while microbially driven biochemical
processes are represented in the middle, biospheric compartment (in blue) and the sediments. Biological element cycling is not completely
closed due to losses through sedimentation of organic carbon and nitrogen, carbonate, metal sulfides, sulfate, and phosphate, and losses to the
atmosphere via denitrification. Regeneration of available forms of these elements is contingent on geological processes: erosion and geothermal
activity. Electron acceptors (oxidants) in the respiratory processes have been arranged from left to right according to increasing capacity to
accept electrons. The redox couples (at pH 7) for the reactions are approximate; the exact values depend upon how the individual reactions are
coupled.
(From
Falkowski et al., 2008
. Copyright 2008 with permission of the American Association for the Advancement of Science.)
be perturbed by anthropogenic activities in order to develop viable strategies for dealing with climate change. The
rate of any increase in atmospheric CO
2
concentration in the future will depend not only on anthropogenic
activities, but on the interaction of biogeochemical and climate processes on the global carbon cycle and inter-
action among the principal carbon pools. There are five global pools (
Figure 18.3
), of which the largest, the
oceanic pool, is estimated at 38000 Gt (giga tons) and is increasing at the rate of 2.3 Gt (giga tons of Carbon)/y
(
Figure 18.3
). The geological carbon pool, comprising fossil fuels, is estimated at 4130 Gt, of which 85% is coal,
5.5% is oil, and 3.3% is gas. Proven reserves of fossil fuel include 678 Gt of coal (production 3.2 Gt/y), 146 Gt of
oil (production 3.6 Gt/y), and 98 Gt of natural gas (production 1.5 Gt/y). Coal and oil each account for
