Information sources Stable isotopes

Amino acid composition data and stable isotope ratios are being evaluated as sources of information to indicate the presence of non-indigenous organics in bone samples intended for radiocarbon analyses. The study is being conducted in the context of the planned 14C measurement of Pleistocene bone samples by high energy mass spectrometric methods. 

The mineral alunite, and its iron equivalent jarosite, is a special case. Alunite (KAl2(S02)2(OH)2) contains four sites where elements containing stable isotopes are found and both the sulfate and hydroxyl anionic groups may provide information on fluid source and condition of formation. 

Radioactive or stable isotopes of noble gases are also used to determine vertical turbulent diffusion in natural water bodies. For instance, the decay of tritium (3H)— either produced by cosmic rays in the atmosphere or introduced into the hydrosphere by anthropogenic sources—causes the natural stable isotope ratio of helium, 3He/ 4He, to increase. Only if water contacts the atmosphere can the helium ratio be set back to its atmospheric equilibrium value. Thus the combined measurement of the 3H-concentration and the 3He/4He ratio yields information on the so-called water age, that is, the time since the analyzed water was last exposed to the atmosphere (Aeschbach-Hertig et al., 1996). The vertical distribution of water age in lakes and oceans allows us to quantify vertical mixing. 

Subsequent marine studies have shown that there are often several important plant sources of carbon, and a multiple stable-isotope approach has been widely adopted to resolve this more complex situation. Stable isotopes of sulfur, successfully combined with carbon measurements, have been particularly valuable for tracing the importance of detrital foods that are difficult to identify or quantify visually (41). The information gained in these isotopic studies has allowed ecologists to powerfully verify or refute hypotheses about the importance to consumers of certain food sources (42). 

Stable isotope investigations on plant biominerals. In contrast, only a limited number of studies have investigated the stable isotope composition of plant biominerals as a source of paleoenviron-mental information. Silica extracted from the Eocene paleosols of Axel Heiberg Island in arctic Canada were found to have notably high stable oxygen isotope value, leading to the suggestion that the mineral represented an accumulation of... 

Stable isotope compositions are useful tracers of the sources and transformations of marine materials however, they carry no direct information about the rates and dates of the associated processes. Such temporal distinctions are possible, however, with the many different naturally occurring radioactive isotopes (Fig. 5.1) and their wide range of elemental forms and decay rates. These highly dependable atomic clocks decay by nuclear processes that allow them to be detected at veiy low concentrations. Long-lived and Th... 

Other information on the sources and dispersion of anthropogenic lead can be derived from the stable isotope ratios of lead (e.g. ° "Pb/ ° Pb) which vary from one mining source to another because of differing Pb/U and Pb/Th for geological sources of lead. In particular, US leaded gasoline for many years had a ° "Pb/ ° Pb ratio of > 1.20, whereas European... 

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