Climatic temperatures, isotope fractionation

But isotope fractionation at climatic temperatures is a function of the frequencies of the chemical bonds [16]. We quote from Herzberg [19] as follows "One would expect the -C-H bond to have essentially the same electronic structure and therefore the same force constant in different molecules, and similarly for other bonds. This is indeed observed". For the -C-H bonds the vibrational frequencies in lignin and in cellulose are almost equal, but in fact differ by 6 percent [19] because cellulose is a multiple alcohol (H-C-0-H)n and lignin is a polymer containing... 

Oxygen isotopes of phosphate in seawater. Use of the oxygen isotopic composition of phosphate in biogenic hydroxyapatite (bones, teeth) as a paleotemperature and climate indicator was pioneered by Longinelli (1966), and has since been fairly widely and successfully applied (Kolodny et al., 1983 Shemesh et al., 1983 Luz et al., 1984). The relationship between phosphate oxygen isotopic fractionation and temperature originally proposed (Longinelli and Nuti, 1973) has been confirmed by later work (Blake et al., 1997 Colman, 2002). 

The ratio of oxygen isotope 18 to oxygen isotope 16 is often used to measure past climate because it is directly related to atmospheric temperature. Oxygen isotopes are used as a proxy for temperature in studies of marine sediments, ice cores, faunal remains, and other materials. The abundance of the two isotopes depends on temperature-related fractionation processes such as evaporation, condensation, and transpiration. 

Isotopic composition of smectites in bentonites from Ishirini indicate an alteration of the pyroclastic rocks predominantely by heated meteoric water at temperatures ranging from 30 to 90 °C. Alteration by fluids similar to the present day hydrothermal solutions from the deep geothermal reservoir can be excluded. Geothermometric calculations based on 5 0 and 6D ratios of the smectites can only provide a temperature range for the bentonite formation. In addition, several uncertainties have to be considered, e.g. the reability of the fractionation factors, deviations in the climatic conditions or isotopic exchange with fluids percolating through the newly formed bentonites. 

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