Oxygen isotopes definition

A quite definite dependence of the oxygen isotopic composition of the ore minerals on the characteristic mineral parageneses is observed for the Krivoy Rog and KMA (see Fig. 95). The values obtained for 5 0 fall into four groups. 

Dediazoniation does not show a significant solvent isotope effect ( h2o/ d2o = 0.98 0.01 Crossley et al., 1940 Swain et al., 1975 a). This result is definitely not consistent with a mechanism in which charge is built up on oxygen in the rate-limiting transition state, as expected for an ANDN-like process. 

The work of Thiemens, Mauersberger, and their collaborators has now definitively established a pervasive mass independent isotope fractionation for oxygen containing molecules found in the atmosphere, upper atmosphere, and in space. These results, initially surprising because they are inconsistent with ordinary equilibrium... 

A reliable authenticity assessment is concluded from the simultaneous consideration of multielement IRMS and enantioselective analysis. The differences of the stable isotope ratios of linalool and linalyl acetate are depicted as a three-dimensional plot of A values (d values of linalool minus d values of linalyl acetate for oxygen, hydrogen and carbon) (Fig. 17.15). This plot shows that the commercial samples S1-S5 are different from all the other samples investigated. Linalool and linalyl acetate of S1-S5 definitely are not genuine lavender oil compounds. 

The definitions of elements and isotopes were presented in sections 5.1 and 5.2. Elements are defined by the number of protons in the nucleus of their atoms. Hydrogen has one proton and oxygen has eight protons. Isotopes are defined as variations of a given element, differing from each other by the number of neutrons. As presented in section 5.2, the hydrogen isotopes are... 

In other districts, for instance in the KMA, reduction of oxide sediment to magnetite and siderite by organic matter probably was of great ore-forming importance (Plaksenko, 1966). Isotopic data on this district are still insufficient for definite conclusions in two out of three analyses (see Fig. 96) the S 0 of coexisting oxides are similar, and in one the magnetite oxygen is... 

If we subtract 1 and multiply by 1000 on both sides, the left side of the equation is equal to the definition of of O2 with respect to the standard SMOW, and the right side is +20%o. This value is lower than the measured value of 23.5%o because roughly half of the oxygen production by photos5mthesis occurs on land and about half in the ocean. O2 from terrestrial photosynthesis is 4%o-8%o heavier than SMOW because evaporation exceeds precipitation in the water of leaves, where most of the photosynthesis of the terrestrial biosphere occurs. The mean 8 0 from oceanic and terrestrial photosynthesis is thus +22%o to +24%o. If one assumes that the partitioning of photosynthesis between the land and ocean remained the same and fractionation factors did not change in the past, then the sole reason for changes in the 8 0-02 of the atmosphere trapped in bubbles of the ice is due to the variation in the isotope ratio of seawater. 

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