The Effects of Atomic Radiation on Oceanography and Fisheries (1957) / Chapter Skim
Currently Skimming:
ISOTOPIC TRACER TECHNIQUES FOR MEASUREMENT OF PHYSICAL AND CHEMICAL PROCESSES IN THE SEA AND THE ATMOSPHERE
ISOTOPIC TRACER TECHNIQUES FOR MEASUREMENT OF PHYSICAL AND CHEMICAL PROCESSES IN THE SEA AND THE ATMOSPHERE
Pages 103-120
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 103... ...
It is this phenomenon of mass movement dominance, and the relative unimportance of diffusive transfer except in special cases, that makes the tracer technique so powerful; a tagged isotope for each element is not required, and one can choose for each particular study the elements most useful for tracing the movement of a mass of heterogeneous material. As mentioned at several points in this report, both artificial and natural isotopic tracers may be used for the study of transfer phenomena in the sea and the atmosphere.
|
From page 104... ...
From these considerations it seems evident that the critical data in studies of atmospheric and oceanic mixing and interaction will come from the use of the naturally occurring isotopic tracers, which reflect in their material balance adjustments the differential rates of transfer from source, through reservoir, to sink, and loss by decay. It is from these transfer rates, adjusted to the steady state geochemical and geophysical cycles of the various elements, that we can hope to gain an understanding of the long period variations in natural transfer phenomena.
|
From page 105... ...
. The steady state isotopic separation of the stable isotopes C12 and C15 produces a C12 concentration in surface ocean water bicarbonate and shell carbonate which is about 2.5 per cent higher than the C12 concentration in terrestrial plants.
|
From page 106... ...
Von Buttlar and Libby calculated that, with such a production rate, and with the observed surface sea concentration of about 0.24 T.U., then the mixed layer of the sea is about 100 meters deep if one assumes that all the tritium of the sea is in the mixed layer. Though this depth is consistent with observational data on the sea, such a calculation assumes that the mixed layer is sealed off from the deep sea so that no tritium mixes below the thermocline, and the question then arises as to just how much mixing across the thermocline does, in fact, occur.
|
From page 107... ...
shows that for reasonable internal mixing rates of the sea, most of the world inventory of tritium must actually be in the deep sea below the thermocline. Thus for a deep water replacement time, or residence time of a water molecule in the deep sea before mixing into the surface layer, of 0 to 1000 years, and with a surface concentration of 0.24 T.U., the tritium flux into the sea must be between 7.6 and 0.3 atoms cm2/sec.
|
From page 108... ...
Assuming a tritium production rate of 1.4, half of which is in the stratosphere, the tritium concentration of stratospheric water vapor is then calculated to be at least 300,000 tritium units. This is an astounding concentration factor relative to tropospheric water vapor.
|
From page 109... ...
Since H2O1S is the most volatile isotopic species, the water vapor over the oceans is depleted in the heavy isotopes relative to the surface ocean water. As this vapor moves over the continents, the first rain to fall out is enriched in the heavy isotopes relative to the vapor, again because of the higher volatility of the lightest species.
|
From page 110... ...
The surface layers of the oceans are in general enriched in the heavy isotopes relative to mean ocean water because of the net storage of H2O10 in the stagnant and circulating fresh water and vapor; the extent of this enrichment reflects the hold up at the boundary of the mixed surface layer, namely the thermocline. On the other hand, the deeper layers of the ocean are depleted in deuterium and oxygen 18, relative to mean ocean water, because of the influx of glacial melt water in polar latitudes, the glacial waters having 8 values at the lightest ends of the ranges cited in the preceding paragraphs.
|
From page 111... ...
The intent here is to point out that the isotopic transfer rates involved in this problem of the isotopic composition of atmospheric oxygen, and the variations in the isotopic composition and amounts of oxygen dissolved in ocean waters, may well be important parameters for the study of transfer phenomena in the oceans and the atmosphere and the interaction between them. Carbon 13 About one per cent of natural carbon consists of the stable isotope C12; the ratio C1S/C12, and thus effectively the Cls concentration, in natural material shows a range of variation of about 6 per cent.
|
From page 112... ...
Comparing these figures with the ones given in the above table, we see that roughly 5.6/17.4 or 'J' of all the solid fission products so far produced, by all fission, have been distributed over the atmosphere, the land, and the sea, by atomic weapons testing. The most important of these elements for studying mixing rates in the sea should be cesium 137, which being soluble, should be an excellent tracer for the mixing rate of surface ocean water down through the thermocline.
|
From page 113... ...
In Section II above it was concluded that the world inventory of tritium was about 20 kg, with about 5 kg in the mixed layer of the sea, and about 15 kg in the deep sea. The Chicago data show that the tritium content of the surface ocean waters has increased by at least a factor of four, indicating that the order of magnitude of 20 kilograms of man-made tritium has so far rained out into the ocean.
|
From page 114... ...
The importance of a great many vertical profiles of this sort from both oceans, and their fundamental import for knowledge of the mixing rates in the ocean, is obvious. Because of the requirements of steady state balancing, the amounts of water transferred, per unit time, downward and upward through the thermocline in the sea must be equal, but because the mixed layer contains only about 2 per cent of the sea, this balance requires that a water molecule remain, on the average, some 50 times longer below the thermocline than above.
|
From page 115... ...
The exchange rate of carbon dioxide between atmosphere and sea may be deduced from considerations of the steady state relationships between the exchange rate and the radioactive decay rate; this type of evaluation is independent of considerations based on the magnitude of the Suess effect and the kinetics of the transient state. The general equations governing the transfer of a radioactive isotope between its various exchange reservoirs have been given by Craig (1957(a)
|
From page 116... ...
Thus the figure cited above of a 0.74 per cent increase in atmospheric activity for each year of atmospheric residence time, indicates that the residence time of a CO2 molecule in the atmosphere, before entering the sea, is about 7 years, corresponding to the 5 per cent activity difference between carbon in the atmosphere and in the mixed layer of the sea. An independent calculation of the atmospheric residence time can be made by considering only the steady-state material balance in the atmosphere as a function of the production rate of radiocarbon, taken as (2 ± .5)
|
From page 117... ...
The various considerations outlined above are all consistent with any deep-sea residence time of carbon up to a few thousand years, and do not yield any closer estimate for this figure. Recent unpublished data by Broecker and coworkers at the Lamont Geological Observatory indicate that the bicarbonate of deep ocean waters probably averages about 8 per cent lower in C14 content than the surface mixed layer, corresponding to a radiocarbon "age" of the order of 670 years.
|
From page 118... ...
It is fortunate that the introduction of such experiments came at a time when geochemists were well underway towards the understanding of natural transfer phenomena by means of studies based on naturally occurring isotopes in their steady state biogeochemical cycles. It should be clear that the need for this knowledge is such that every effort should be
|
From page 119... ...
. Distribution, production rate, and possible solar origin of natural tritium.
|
From page 120... ...
1951. Isotopic composition of oxygen in air dissolved in Pacific ocean water as a function of depth.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.