Hydrogen isotope variations

Isotope variations are most pronounced in atoms with low atomic weights hydrogen, carbon, oxygen and sulfur. 

The relative mass difference between the two stable isotopes and (deuterium, D) is larger than for any other isotope pair. Because of that hydrogen shows the greatest isotopic fractionation. The content of heavy water HDO in ocean water corresponds to 0.015 atomic% and a 8D-value near 0. light water, H O, has the higher vapor pressure and is to some extent enriched in the vapor. The difference becomes greatest when the temperature is low. Measurements of precipitation show that water near the equator has a hydrogen isotopic composition near that of ocean water whereas snow near the poles may have 6°-values below -300%o. 

Oxygen Isotope Variations and Temperature Variations 400 000 Years Agp 

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Fig. 3.4 Hydrogen isotope variations in mantle-derived materials (modified after Bell and Ihinger, 2000)...

Epstein S, Sharp RP, Gow AJ (1965) Six-year record of oxygen and hydrogen isotope variations in South Pole flm. J Geophys Res70(8) 1809-1814... 

Atmospheric methane has a mean 5 C-value of around —47%c (Stevens 1988). Quay et al. (1999) presented global time series records between 1988 and 1995 on the carbon and hydrogen isotope composition of atmospheric methane. They measured spatial and temporal variation in and D with a slight emichment observed for the southern hemisphere (—47.2%c) relative to the northern hemisphere (—47.4%o). The mean 5D was —86 3%c with a 10%o depletion in the northern relative to the southern hemisphere. 

Fricke HC, Wickham SM, O Neil JR (1992) Oxygen and hydrogen isotope evidence for meteoric water infiltration during mylonitization and uphft in the Ruby Mountains - East Humboldt Range core complex, Nevada. Contr Miner Petrol 111 203-221 Fricke HC, Clyde WC, O Neil JR (1998a) Intra-tooth variations in 5 0 (PO4) of mammalian tooth enamel as a record of seasonal variations in continental climate variables. Geochim Cosmochim Acta 62 1839-1850... 

Peters KE, Rohrbach BG, Kaplan IR (1981) Carbon and hydrogen stable isotope variations in kerogen during laboratory-simulated thermal maturation. Am Assoc Petrol Geol Bull 65 501-508... 

The investigation of body fluids with respect to nutrient (essential) elements and toxic elements -which are challenging topics for analytical chemistry - include the determination of concentrations at the trace and ultratrace level. However, isotope variation and isotope effects (especially of lighter elements such as hydrogen, carbon, nitrogen, oxygen but also of iron and calcium) have also been studied.22 23 The most frequently applied mass spectrometric technique for the analysis of body fluids today, which fulfils all requirements and also results in accurate and precise data, is ICP-MS. 

Alhambra and co-workers adopted a QM/MM strategy to better understand quantum mechanical effects, and particularly the influence of tunneling, on the observed primary kinetic isotope effect of 3.3 in this system (that is, the reaction proceeds 3.3 times more slowly when the hydrogen isotope at C-2 is deuterium instead of protium). In order to carry out their analysis they combined fully classical MD trajectories with QM/MM modeling and analysis using variational transition-state theory. Kinetic isotope effects (KIEs), tunneling, and variational transition state theory are discussed in detail in Chapter 15 - we will not explore these topics in any particular depth in this case study, but will focus primarily on the QM/MM protocol. 

The long time scales (104 to 10s m.y.) involved in deformation and synkinematic isotope exchange in white mica provide a robust, long-term average of meteoric water-rock interaction, characteristic for the time scales of major readjustments in surface elevation. Thus the hydrogen isotope record in recrystallized muscovite provides a direct link between the tectonic and fluid flow history in the shear zone and temporal variations in meteoric water composition due to changing surface elevation. 

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