Water Cycle
71
tially enclosed seas in areas of high evaporation. Most of the dissolved
material is in the form of simple ions or cation-anion complexes. The
principal cations, in order of abundance, are Na+, Mg+ + Ca+ +, and K+;
the principal anions are Cl-, SO;-, HC0 3 .
As is discussed in the following, the different water reservoirs found
in and on earth differ isotopically. First, however, we list some definitions concerning water of different origin (after WHITE, 1957a, b).
Meteoric water: The term "meteoric" applies to water that was recently involved in atmospheric circulation.
Connate water: Connate water is "fossil" water, which has been trapped in the
sediments at the time of burial.
Formation water: Formation water is present in rocks immediately before
drilling (it may be a useful nongenetic term for waters of unknown age and origin
but should not replace the genetic concept of connate water).
Metamorphic water: Metamorphic water is water that is or has been associated
with rocks during their metamorphism.
Hydrothermal water: This term refers to any water that is warm or hot relative
to its surrounding environment and has no genetic implications.
Magmatic water: Magmatic water is in or is derived from magma. Most (or
perhaps all) magmatic waters may actually be recycled through remelting or partial
melting of sedimentary and volcanic rocks.
Juvenile water: Juvenile water is new water that is in or is derived from primary
magma or other matter and has not previously been a part of the hydrosphere.
One can look upon the hydrologic cycle as a sequential, dynamic
system in which water moves as a result of such processes as condensation, precipitation, evaporation, infiltration, and runoff. In order to understand the variations in isotopic composition in natural waters it is
necessary to establish the nature of the variations in precipitations, the
melting of polar ice, continental runoff, etc., which have been extensively
discussed by FRIEDMAN et al. (1964).
The natural water cycle has been compared with a multiple-stage
distillation column with reflux of the condensate to the reservoir (EpSTEIN and MAYEDA, 1953). The oceans correspond to the reservoir, and
the ice fields at the Poles correspond to the highest stages of the column.
(The isotopic composition of snow near the South Pole is deficient in 18 0
by 60%0 compared with ocean water (ALDAZ and DEUTSCH, 1967).
As has been mentioned earlier, the most efficient process in creating
variations in the isotope ratios of water is by vapor pressure differences.
In all processes concerning the water cycle the hydrogen isotopes are
fractionated in proportion to the oxygen isotopes, because a similar
difference in vapor pressures exists between H20 and HDO on one side
and H2 16 0 and H2 18 0 on the other side. Therefore, the hydrogen and
oxygen isotope distributions are correlated in meteoric waters. CRAIG
(1961 a) has given the following relationship:
bD = 8b 18 0 + 10.
71
tially enclosed seas in areas of high evaporation. Most of the dissolved
material is in the form of simple ions or cation-anion complexes. The
principal cations, in order of abundance, are Na+, Mg+ + Ca+ +, and K+;
the principal anions are Cl-, SO;-, HC0 3 .
As is discussed in the following, the different water reservoirs found
in and on earth differ isotopically. First, however, we list some definitions concerning water of different origin (after WHITE, 1957a, b).
Meteoric water: The term "meteoric" applies to water that was recently involved in atmospheric circulation.
Connate water: Connate water is "fossil" water, which has been trapped in the
sediments at the time of burial.
Formation water: Formation water is present in rocks immediately before
drilling (it may be a useful nongenetic term for waters of unknown age and origin
but should not replace the genetic concept of connate water).
Metamorphic water: Metamorphic water is water that is or has been associated
with rocks during their metamorphism.
Hydrothermal water: This term refers to any water that is warm or hot relative
to its surrounding environment and has no genetic implications.
Magmatic water: Magmatic water is in or is derived from magma. Most (or
perhaps all) magmatic waters may actually be recycled through remelting or partial
melting of sedimentary and volcanic rocks.
Juvenile water: Juvenile water is new water that is in or is derived from primary
magma or other matter and has not previously been a part of the hydrosphere.
One can look upon the hydrologic cycle as a sequential, dynamic
system in which water moves as a result of such processes as condensation, precipitation, evaporation, infiltration, and runoff. In order to understand the variations in isotopic composition in natural waters it is
necessary to establish the nature of the variations in precipitations, the
melting of polar ice, continental runoff, etc., which have been extensively
discussed by FRIEDMAN et al. (1964).
The natural water cycle has been compared with a multiple-stage
distillation column with reflux of the condensate to the reservoir (EpSTEIN and MAYEDA, 1953). The oceans correspond to the reservoir, and
the ice fields at the Poles correspond to the highest stages of the column.
(The isotopic composition of snow near the South Pole is deficient in 18 0
by 60%0 compared with ocean water (ALDAZ and DEUTSCH, 1967).
As has been mentioned earlier, the most efficient process in creating
variations in the isotope ratios of water is by vapor pressure differences.
In all processes concerning the water cycle the hydrogen isotopes are
fractionated in proportion to the oxygen isotopes, because a similar
difference in vapor pressures exists between H20 and HDO on one side
and H2 16 0 and H2 18 0 on the other side. Therefore, the hydrogen and
oxygen isotope distributions are correlated in meteoric waters. CRAIG
(1961 a) has given the following relationship:
bD = 8b 18 0 + 10.