Oxygen tracer applications

Isotopes of oxygen and hydrogen are useful tracers of water sources because they are constituents of the water molecule itself and because they are conservative in aquifers at near-surface temperatures. Isotopic techniques take advantage of the fact that lakes and their surrounding ground-water systems are usually isotopically distinct. Applications of stable isotopes for the study of lakes were first described by Dincer (10) and were discussed in several subsequent review articles (11-14). Most applications of isotopic techniques to lake systems are designed for the determination of water balances, nutrient-uptake studies, and paleotemperature reconstructions. 

Activation with 14 MeV neutrons has been used to determine the oxygen content of various metals such as beryllium 20>, Cl, F, O, Na, Si, and various rare earths in complex molten salt electrolytes 45>, the protein content of food products by means of the nitrogen content 46>, i60/180 and 14N/15N isotopic ratios in stable isotope tracer experiments 47,48), and in a wide variety of other applications. One application we... 

Krouse and Mayer (2000) present an in-depth review and several case smdies of the use of stable sulfur and oxygen isotopes of sulfate as hydrologic tracers in groundwater. In addition, the use of sulfur isotopes for investigations of hydrological processes in catchments has been reviewed by Mitchell et al. (1998). Thus, what is presented here is just a brief overview of the application of sulfur isotopes in hydrologic studies. 

Because the longest-lived oxygen radioisotope, 0, has a half-life of only 124 s, the separated isotopes 0 and are valuable in tracer experiments. The nuclear magnetic moment of 0 gives it application in determining molecular structure by nuclear magnetic resonance measurements. 

Watson EB, Cherniak DJ (1997) Oxygen diffusion in zircon. Earth Planet Sci Lett 148 527-544 Wendlandt RW (1991) Oxygen diffusion in basalt and andesite melts Experimental results and discussion of chemical versus tracer diffusion. Contrib Mineral Petrol 108 463-471 West AR (1984) Solid State Chemistry and Its Applications. John Wiley and Sons, New York Whipple RTP (1954) Concentration contours in grain boundary diffusion. Phil Mag 45 1225-1236 White AF, Peterson MI (1990) Role of reactive-surface area characterization in geochemical kinetic models. In Melchior DC, Bassett RL (eds) Chemical Modeling of Aqueous Systems. II. Am Chem Soc Symp 416 461-475... 

Here I briefly review some recent applications of using oxygen and its isotopes as diagnostic tracers of the global carbon cycle. The focus is on atmospheric O2 and CO2 and the oxygen isotope... 

Oxygen consists of three stable isotopes 0, " O and " O. For most applications only the ratio between the more abundant Lso-topes, 0 and O, is measured. If all fractionation processes in the environmental system were purely mass-dependent, measurements of 0/ 0, would be redundant, as they could be predicted from the 0/ 0 ratio. However, it has recently been ob.served that photochemical exchange between O2, Oi, and CO, in the stratosphere involves mass-independent fractionation among the oxygen isotopes (1990 Thiemens et al., 1993a, b Thiemens, 1999). Thereby O2 becomes anomalously depleted, while CO2 becomes anomalously enriched. Because of this, measurements of 0/ 0 in atmospheric O2 and/or CO2 provide an independent piece of information. Conveniently, one may define an O anomaly tracer (A 0) (Thiemens et n/., 1995b)... 

One of the first applications of ocean radiocarbon data was as a constraint on the vertical diffusivity, upwelling, and oxygen consumption rates in the deep waters below the main thermocline. As illustrated in Figure 2, the oxygen and radiocarbon concentrations in the North Pacific show a minimum at mid-depth and then increase toward the ocean seabed. This reflects particle remineralization in the water column and the inflow and gradual upwelling of more recently ventilated bottom waters from the Southern Ocean. Mathematically, the vertical profiles for radiocarbon, oxygen (O2), and a conservative tracer salinity (5) can be posed as steady-state, 1-D balances ... 

Researchers operating with the TLC technique have some general options, shown in Fig. 1. The pure (unencapsulated) TLC substance applied in very thin films onto a flat surface offers temperature field measurements with a spatial resolution of about 800 nm. But, unencapsulated TLCs require sophisticated application techniques, and the pure TLC substance is very sensitive to UV light and contaminatirMis, particularly oxygen from the air. More common are micro-encapsulated TLCs which are stable and easier to handle. They are available as complete foils, in binder mixtures for spray applications, and as tracers. With the latter it is possible to acquire the temperature distribution in liquid flows. 

Scientific research is another major application of radionuclides. Chemists use tagged atoms as radioactive tracers to study the mechanism, or series of individual steps, in complicated reactions. For example, by using water containing radioactive oxygen, scientists have determined that the oxygen in the glucose, CgHi20g, formed in photosynthesis... 

The total amount of UV radiation, together with the effects of any unreacted intermediates, singlet oxygen, other radicals and acids can cause fatigue of the molecule. Commercial applications could include ophthalmic lenses, agricultural films, UV source detection, UV curing system testing, and security tracers. 

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