Oxygen isotopic enrichment

Rockmann, T C. A. M. Brenninkmeijer, P. Neeb, and P. J. Crutzen, Ozonolysis of Nonmethane Hydrocarbons as a Source of the Observed Mass Independent Oxygen Isotope Enrichment in Tropospheric CO, J. Geophys. Res., 103, 1463-1470 (1998). 

FIGURE 2.3 Heavy oxygen isotope enriched mass independent fractionation, experiment [59] and theory [13]. 

Duplessy J.-C., Labeyrie L., and Waelbroeck C. (2002) Constraints of the ocean oxygen isotopic enrichment between the Last Glacial Maximum and the Holocene paleoceanographic implications. Quat. Sci. Rev. 21, 315-330. 

In this equation the red O signifies oxygen enriched in Its mass 18 isotope analysis of isotopic enrichment was performed by mass spectrometry... 

It follows that, depending on the temperature, whenever limestone precipitates, it includes the oxygen isotope in which the water is rich in sea waters, for example, the limestone is enriched in oxygen-18 ... 

If the reaction is carried out in water enriched in the heavier oxygen isotope 180, (a) will lead to an alcohol which is 180 enriched and an acid which is not, while (b) will lead to an l80 enriched acid but a normal alcohol. Most simple esters are in fact found to yield an lsO enriched acid indicating that hydrolysis, under these conditions, proceeds via (b) acyl/oxygen fission (p. 238). It should of course be emphasised that these results are only valid provided that neither acid nor alcohol, once formed, can itself exchange its oxygen with water enriched in 180, as has indeed been shown to be the case. 

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. 

Figure 2.3 Changes in the heavy isotope content of oxygen and hydrogen in the urine with time after administration of The and 0 are diluted by the formation of H2O from oxidation of fuels and particularly that ingested in food and drink. The 0 in water is diluted from the production of CO2 via the oxidation of the fuels. The difference in the slopes indicates the rate of CO2 production. The label heavy isotope content is actually the isotopic enrichment. Physical activity, for example, increases fuel oxidation (i.e. respiration) and therefore greater dilution of...

This method derives from the observation that the degree of enrichment in a set of cogenetic silicate minerals (expressed as oxygen isotope index I- 0) can be related to bond strengths in minerals (Taylor, 1968). The oxygen isotope index for phase A is defined by... 

Any isotope fractionation occurring in such a way that the products are isolated from the reactants immediately after formation will show a characteristic trend in isotopic composition. As condensation or distiUation proceeds, the residual vapour or liquid will become progressively depleted or enriched with respect to the heavy isotope. A natural example is the fractionation between oxygen isotopes in the water vapour of a cloud and the raindrops released from the cloud. The resulting decrease of the iso/i o ratio in the residual vapour and the instantaneous isotopic composition of the raindrops released from the cloud are shown in Fig. 1.4 as a function of the fraction of vapour remaining in the cloud. 

Thus, separate levels of the oceanic crust are simultaneously enriched and depleted in relative to normal mantle values because of reaction with sea water at different temperatures. Muehlenbachs and Clayton (1976) and Gregory and Taylor (1981) concluded that the 0 enrichments are balanced by the depletions which acts like a buffer for the oxygen isotope composition of ocean water. 

Another oxygen isotope fractionation effect is documented in CO2 samples collected between 26 and 35 km altitude, which show a mass - independent enrichment in both 0 and 0 of up to about 15%c above tropospheric values (Thiemens et al. 1995). The enrichment of stratospheric CO2 relative to tropospheric CO2 should make it possible to study mixing processes across the tropopause. 

Muehlenbachs K, Byerly G (1982) 0 enrichment of silicic magmas caused by crystal fractionation at the Galapagos Spreading Center. Contr Miner Petrol 79 76-79 Muehlenbachs K, Qayton RN (1972) Oxygen isotope studies of fresh and weathered submarine basalts. Can J Earth Sci 9 471 79... 

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