Oxygen isotopes standard

Table 2.5 gives the 5 0-valnes of commonly used oxygen isotope standards on both scales (parenthesis denote calcnlated values). 

FIGURE 2.10 (a) An oxygen isotope plot for chondritic meteorites showing the two main meteorite trends, relative to the terrestrial mass-dependent fractionation (MDF) trend (which passes through the oxygen isotope standard SMOW). The CCAM line (dashed) represents a mixing line defined by separated minerals from refractory CAI inclusions. Amoeboid olivines plot at the lower 160-rich end of this line. The aqueous alteration trend is shown in more detail in (b) below. 

NBS-19 Carbon and oxygen isotopic standard comprised of TS-Umestone. 

Oxygen isotopes Standard mean ocean water ... 

Eig. 4. The bulk oxygen isotopic composition of different meteorite classes where (—) is the terrestial fractionation line. The 5 notation refers to the normalized difference between or ratios to those in standard mean ocean water (SMOW) in relative units of parts per thousand. The... 

Valley, J.W., Kitchen, N., Kohn, M.J., Niendorf, C.R. and Spicuzza, M.J. 1995 UWG-2, a garnet standard for oxygen isotope ratios strategies for high precision and accuracy with laser heating. Geochimica et Cosmochimica Acta 59 5223-5231. 

Craig H (1957) Isotopic standards for carbon and oxygen and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim Cosmochim Acta 12 133-149. 

Determining the temperature at which ancient sediments were formed entails two successive experimental stages (1) extracting the carbon dioxide from the sediments and (2) determining the relative amounts of the oxygen isotopes in the extracted carbon dioxide. Treating a sediment with a standard acid, such as hydrochloric or sulfuric acid, dissolves the calcium and magnesium carbonates in the sediments and... 

SMOW Acronym for Standard Mean Ocean Water, used as a chemical and isotopic reference standard, for example, when studying oxygen isotope ratios. soap A cleaning agent made by the reaction of an oil or fat with an alkali such as soda. 

Substantial abundance anomalies occur among the heavy oxygen isotopes 170 and 180, which are underabundant by up to about 4 per cent relative to 160 in oxide grains of certain of the CAIs, compared with the bulk composition in which the isotope ratios are closer to a terrestrial standard. The intriguing feature of these anomalous ratios is that, in common with some other meteorites, but in contrast to terrestrial and lunar samples, the relative deviations of the two heavy isotopes are equal most normal fractionation processes would cause 180 to have twice the anomaly of 170, as indeed is observed in terrestrial samples and more differentiated meteorites, where the anomalies are also usually much smaller. While there has been speculation that there might be a substantial admixture of pure 160 from a supernova, there are fractionation mechanisms that may be able to account for the effect, e.g. photo-dissociation of molecules affected by selfshielding (R. Clayton 2002). In this case, it is possible that the terrestrial standard is enriched in the heavy O-isotopes while the inclusions have more nearly the true solar ratio. 

Craig H (1957) Isotopic standards for carbon and oxygen and correction factors for mass spectro-metric analysis of carbon dioxide. Geochim Cosmochim Acta 12 133-149 DeNiro MJ, Epstein S (1978) Influence of diet on the distribution of carbon isotopes in animals. Geochim Cosmochim Acta 42 495-506... 

Oxygen isotopes were analyzed using the technique of Clayton and Mayeda (69). Data are presented using the standard 6 notation relative to Standard Mean Ocean Water (SMOW). 

That is, the 0/ 0 ratio in a sample is compared with a standard, and the difference is expressed as per mil (per thousand). The standard for oxygen isotopes is standard mean ocean water (SMOW). The exchange reaction of 0 and O between two minerals is a heterogeneous reaction and may be written as, e.g.. 

Table 4.2 and similar tables should not be used as the source of isotopic compositions of terrestrial standards for high-precision isotopic measurements. While Table 4.2 gives a good overview of the abundances of the isotopes, the values in the table do not always represent state-of-the-art isotopic measurements. Nor do they attempt to take into account the isotopic fractionations that occur in terrestrial materials. Typically, an isotope system that has been measured for many years has a convention about how isotopic ratios are reported. For example, oxygen isotopic compositions are typically reported relative to the Vienna determination of Standard Mean Ocean Water... 

Oxygen isotopic compositions for bulk chondrites, after Clayton (2004). By convention, 170/160 and 180/160 ratios are plotted as deviations from the composition of standard mean ocean water (SMOW) in units of parts per thousand (permil). The 8 values are calculated as follows S170 = [((170/160)sampie/(170/160)SMOw)-1] x 1000, and similarly for S180. 

Oxygen isotopic compositions (relative to standard mean ocean water, SMOW) of several mineral grains in three Stardust particles, each grain denoted by a separate symbol. Open circles are from a CAI comet particle. After McKeegan et al. (2006). 

Various isotope standards are used for reporting isotopic compositions the composition of each of the standards has been defined as 0 per mil. Oxygen and hydrogen isotopic compositions are commonly reported relative to standard mean ocean water (SMOW or V-SMOW) (17). 

Fig. I. Tile bulk oxygen isotopic composition of different meteorite classes si lie it1 i —i is the lciicsiii.il fractionation line. The, 1 notation refers lo ihc normalized difference between O I,r O ur 1 O O ratios lo iliuse in standard...

Oxygen isotopes have been the most thoroughly studied isotopes in carbonate mineral systems. There are three stable isotopes of oxygen 160 = 99.763%, 170 = 0.0375% and 180 = 0.1995% (Garlick, 1969). The fractionation of 180 relative to 160 is commonly measured and reported as the value of 8180 relative to a standard. Two standards have been widely used in reporting 8180 values. The most common one in general usage now is "SMOW," which stands for standard mean ocean water. 

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