Chapter 1
The Carbonate System in Marine Environments
EJ. Millero
1.1
Introduction
The major portion of carbon in the oceans occurs in the carbonate system. This system involves the following equilibria
(1.1)
Ca 2 + + CO~- ~ CaC03(s)
(1.4)
The carbonate system is very important since it regulates the pH of sea water, and
controls the circulation of CO2 between the biosphere, the lithosphere, the atmosphere
and the oceans. Recent interest in the carbonate system in the oceans has resulted from
the "greenhouse effect" of CO 2 , The concentration of CO2 in the atmosphere has increased in the twentieth century (Fig. 1.1) (Keeling and Whorf 1994; Neftel et al. 1994
Since CO2 can absorb infrared (IR) energy, this increase may cause the temperature
of the earth to increase and could eventually melt the polar ice caps. The increase in
CO2 is related to the burning of fossil fuels (coal, petroleum and natural gas) and the
production of cement. The atmospheric CO2 enters the oceans across the air-sea interface and participates in the equilibrium processes outlined by Eq. 1.1 to 1.4. It also
can be used by ocean plants in primary productivity
The adsorption of CO 2 by the oceans is quite complicated, since the rates of movement of the gas across the interface and from surface to deep waters varies with latitude, time, and season. Diurnal and seasonal variations in the carbonate system are
caused by the removal of CO2 by photosynthesis and solar heating. If the oceans were
well-mixed and in equilibrium with the atmosphere, most of the increased CO 2 would
be absorbed. This, however, is not the case, and the ocean response to increases in CO 2
is slow due to physical and chemical factors. The exchange involves the hydration of
CO2, which is a slow process relative to ionization. Approximate time scales for the
mixing process can be determined using radioactive tracers to gain some idea of the
mixing times. To use these estimates it is necessary to have some idea of the total car-
The Carbonate System in Marine Environments
EJ. Millero
1.1
Introduction
The major portion of carbon in the oceans occurs in the carbonate system. This system involves the following equilibria
(1.1)
Ca 2 + + CO~- ~ CaC03(s)
(1.4)
The carbonate system is very important since it regulates the pH of sea water, and
controls the circulation of CO2 between the biosphere, the lithosphere, the atmosphere
and the oceans. Recent interest in the carbonate system in the oceans has resulted from
the "greenhouse effect" of CO 2 , The concentration of CO2 in the atmosphere has increased in the twentieth century (Fig. 1.1) (Keeling and Whorf 1994; Neftel et al. 1994
Since CO2 can absorb infrared (IR) energy, this increase may cause the temperature
of the earth to increase and could eventually melt the polar ice caps. The increase in
CO2 is related to the burning of fossil fuels (coal, petroleum and natural gas) and the
production of cement. The atmospheric CO2 enters the oceans across the air-sea interface and participates in the equilibrium processes outlined by Eq. 1.1 to 1.4. It also
can be used by ocean plants in primary productivity
The adsorption of CO 2 by the oceans is quite complicated, since the rates of movement of the gas across the interface and from surface to deep waters varies with latitude, time, and season. Diurnal and seasonal variations in the carbonate system are
caused by the removal of CO2 by photosynthesis and solar heating. If the oceans were
well-mixed and in equilibrium with the atmosphere, most of the increased CO 2 would
be absorbed. This, however, is not the case, and the ocean response to increases in CO 2
is slow due to physical and chemical factors. The exchange involves the hydration of
CO2, which is a slow process relative to ionization. Approximate time scales for the
mixing process can be determined using radioactive tracers to gain some idea of the
mixing times. To use these estimates it is necessary to have some idea of the total car-