38
Chemical Oceanography, 4th Edition
This brief survey provides a discussion of descriptive aspects of estuarine systems. More
is said about the chemistry of estuaries in the next chapter.
1.5
Use of Chemical Tracers in Oceanography
Oceanographers have used various chemical tracers to determine the mixing times of the
water masses in surface and deep ocean waters. They have used tracers such as
1. Conservative tracers (T and S)
2. Isotopic tracers
a. Stable isotopes ( 13 C, 15 N, 18 O)
b. Radioisotopes ( 222 Rn, 228 Rn)
c. Cosmic ray- produced nuclides ( 14 C)
d. Anthropogenic nuclides ( 14 C, tritium, 3 H)
3. Transient tracers (time- varying sources or sinks)
a. Chlorofluorocarbons (CFCs)
b. Carbon-14 ( 14 C)
c. Tritium ( 3 H)
4. Deliberate tracers
a. Sulfur hexafluoride (SF 6 )
b. Fluorescent dyes
Most of the studies have been made using transient tracers such as CFCs and radioactive
elements such as carbon-14 and tritium. They are useful as water mass tracers and for putting timescales on oceanographic processes. The detonation of nuclear weapons during the
late 1950s and early 1960s produced radioisotopes of carbon and hydrogen (Figure 1.43).
These elements were deposited on the surface of the oceans and were gradually mixed
into the deep waters. By following these compounds with time, oceanographers have been
able to obtain a better understanding of the circulation of the oceans. The inputs of these
compounds into the atmosphere are reasonably well known (Figure 1.44).
1.5.1 Carbon-14
Radiocarbon ( 14 C) is being produced in the atmosphere. The protons in cosmic rays shatter
the nucleus of atmospheric atoms and fragment some of them, releasing neutrons. Some of
these neutrons enter the nucleus of 14 N, knocking out a proton, resulting in the formation
of 14 C. The number of nucleons (protons plus neutrons) is the same, but one neutron has
been substituted for a proton. Carbon-14 is radioactive and ejects an electron (beta particle)
and becomes a nitrogen-14 atom. The low- level counting of the beta particle emitted is how
one determines the concentration of 14 C in natural waters. The change in the concentration
of the number of molecules of 14 C (N) can be determined from
N = N 0 e –λt
(1.2)
Chemical Oceanography, 4th Edition
This brief survey provides a discussion of descriptive aspects of estuarine systems. More
is said about the chemistry of estuaries in the next chapter.
1.5
Use of Chemical Tracers in Oceanography
Oceanographers have used various chemical tracers to determine the mixing times of the
water masses in surface and deep ocean waters. They have used tracers such as
1. Conservative tracers (T and S)
2. Isotopic tracers
a. Stable isotopes ( 13 C, 15 N, 18 O)
b. Radioisotopes ( 222 Rn, 228 Rn)
c. Cosmic ray- produced nuclides ( 14 C)
d. Anthropogenic nuclides ( 14 C, tritium, 3 H)
3. Transient tracers (time- varying sources or sinks)
a. Chlorofluorocarbons (CFCs)
b. Carbon-14 ( 14 C)
c. Tritium ( 3 H)
4. Deliberate tracers
a. Sulfur hexafluoride (SF 6 )
b. Fluorescent dyes
Most of the studies have been made using transient tracers such as CFCs and radioactive
elements such as carbon-14 and tritium. They are useful as water mass tracers and for putting timescales on oceanographic processes. The detonation of nuclear weapons during the
late 1950s and early 1960s produced radioisotopes of carbon and hydrogen (Figure 1.43).
These elements were deposited on the surface of the oceans and were gradually mixed
into the deep waters. By following these compounds with time, oceanographers have been
able to obtain a better understanding of the circulation of the oceans. The inputs of these
compounds into the atmosphere are reasonably well known (Figure 1.44).
1.5.1 Carbon-14
Radiocarbon ( 14 C) is being produced in the atmosphere. The protons in cosmic rays shatter
the nucleus of atmospheric atoms and fragment some of them, releasing neutrons. Some of
these neutrons enter the nucleus of 14 N, knocking out a proton, resulting in the formation
of 14 C. The number of nucleons (protons plus neutrons) is the same, but one neutron has
been substituted for a proton. Carbon-14 is radioactive and ejects an electron (beta particle)
and becomes a nitrogen-14 atom. The low- level counting of the beta particle emitted is how
one determines the concentration of 14 C in natural waters. The change in the concentration
of the number of molecules of 14 C (N) can be determined from
N = N 0 e –λt
(1.2)