227
6
Dissolved Gases Other than CO 2
6.1
Introduction
Many workers have examined the concentration of dissolved gases in marine waters like
seawater. Most of the earlier work has been reviewed by Richards (1965) and by Kester
(1975). The most widely studied gas (excluding CO 2 ) is oxygen. Attempts have been made
to separate the physical and biological processes that control the distribution of O 2 . Studies
have also been conducted on the unreactive or conservative gases (N 2 and Ar) and the noble
gases (He, Ne, Kr, and Xe). The regular distribution of the conservative gases has been used
to study the exchange processes across the air–sea interfaces. The irregular distribution of
He and Rn have been used to study exchange processes across the sediment–water interface.
CO 2 is considered in the next chapter on the carbon dioxide or carbonate system. It is
separated from other gases because it is involved in the pH buffer system of marine waters.
Since the source of most gases is the atmosphere, we first consider the composition of the
atmosphere and the subsequent transfer across the air–sea interface.
6.2 Composition of the Atmosphere
The atmosphere is made up of the major gases (N 2 , O 2 , and Ar) and the minor unreactive gases (Ne, He, Kr, and Xe). Water vapor is the most varied component of the atmosphere. Unstable minor gases (CO, NO 2 , and CH 4 ) are produced by biological processes
and human activities. These gases will vary from place to place because of the different
sources and sinks.
Dalton’s law of partial pressures can be used to represent the composition of the atmosphere. This law simply states that the total pressure P T of a mixture of gases in a fixed
volume V is equal to the sum of the partial pressures of the components of the mixture.
For the atmosphere, this gives
P
P P
P
P
P
T
i
N
O
Ar
H O
=
=
+
+
+
∑ 2 2
2
(6.1)
where the values of P i are the partial pressures of the major gaseous components i. If the
gases are assumed to obey the ideal gas law, the partial pressure of each gas is given by
P i = n i RT/ V
(6.2)
6
Dissolved Gases Other than CO 2
6.1
Introduction
Many workers have examined the concentration of dissolved gases in marine waters like
seawater. Most of the earlier work has been reviewed by Richards (1965) and by Kester
(1975). The most widely studied gas (excluding CO 2 ) is oxygen. Attempts have been made
to separate the physical and biological processes that control the distribution of O 2 . Studies
have also been conducted on the unreactive or conservative gases (N 2 and Ar) and the noble
gases (He, Ne, Kr, and Xe). The regular distribution of the conservative gases has been used
to study the exchange processes across the air–sea interfaces. The irregular distribution of
He and Rn have been used to study exchange processes across the sediment–water interface.
CO 2 is considered in the next chapter on the carbon dioxide or carbonate system. It is
separated from other gases because it is involved in the pH buffer system of marine waters.
Since the source of most gases is the atmosphere, we first consider the composition of the
atmosphere and the subsequent transfer across the air–sea interface.
6.2 Composition of the Atmosphere
The atmosphere is made up of the major gases (N 2 , O 2 , and Ar) and the minor unreactive gases (Ne, He, Kr, and Xe). Water vapor is the most varied component of the atmosphere. Unstable minor gases (CO, NO 2 , and CH 4 ) are produced by biological processes
and human activities. These gases will vary from place to place because of the different
sources and sinks.
Dalton’s law of partial pressures can be used to represent the composition of the atmosphere. This law simply states that the total pressure P T of a mixture of gases in a fixed
volume V is equal to the sum of the partial pressures of the components of the mixture.
For the atmosphere, this gives
P
P P
P
P
P
T
i
N
O
Ar
H O
=
=
+
+
+
∑ 2 2
2
(6.1)
where the values of P i are the partial pressures of the major gaseous components i. If the
gases are assumed to obey the ideal gas law, the partial pressure of each gas is given by
P i = n i RT/ V
(6.2)