Dissimilatory sulfate reduction is a microbial catabolic pathway that preferentially processes less massive sulfur isotopes relative to their heavier counterparts. This sulfur isotope fractionation is recorded in ancient sedimentary rocks and generally is considered to reflect a phenotypic response to environmental variations rather than to evolutionary adaptation. Modern sulfate-reducing micro...

We have determined the extent of Se isotope fractionation induced by reduction of selenate by sulfate interlayered green rust (GRSO4), a Fe(II)-Fe(III) hydroxide-sulfate. This compound is known to reduce selenate to Se(0), and it is the only naturally relevant abiotic selenate reduction pathway documented to date. Se reduction reactions, when they occur in nature, greatly reduce Se mobility and...

.......................................................................................................................v RÉSUMÉ............................................................................................................................v INTRODUCTION...............................................................................................................1 Stable isotope chem...

Carbon isotope fractionation by structurally and catalytically distinct ribulose-1,5-bisphosphate carboxylases from one eucaryotic and four procaryotic organisms has been measured under nitrogen. The average fractionation for 40 experiments was -34.1 per thousand with respect to the delta(13)C of the dissolved CO(2) used, although average fractionations for each enzyme varied slightly: spinach ...

Isotope fractionation of electroplated Fe was measured as a function of applied electrochemical potential. As plating voltage was varied from 0.9 V to 2.0 V, the isotopic signature of the electroplated iron became depleted in heavy Fe, with Fe values (relative to IRMM-14) ranging from 0.18( 0.02) to 2.290( 0.006) ‰, and corresponding Fe values of 0.247( 0.014) and 3.354( 0.019) ‰. This study de...

All terrestrial higher plants preferentially assimilate CO 2 relative to CO 2 during photosynthesis as a result of physical and biological isotope fractionation processes, with much larger overall C fractionation by plants using the C 3 photosynthetic pathway (approximate range of 14–27‰) compared to plants using the C 4 pathway (approximate range of 3–6‰). Fractionation against CO 2 in both C ...

Silicon isotope fractionation factors for mantle silicate minerals, including olivine, wadsleyite, ringwoodite, pyroxenes, garnet (pyrope), majorite, and Mg-perovskite, are calculated using density functional theory. Our results show that equilibrium fractionations of Si isotopes are negligible among pyroxenes, olivine, and pyrope, but are significant between olivine and its polymorphs (wadsley...

1. Background 2. Elements, Nuclides, and Stable Isotopes 3. The Mass Spectrometer and Isotope Ratio Measurement 4. Isotope Fractionation 5. Temperature and Fractionation 6. Stable Isotopes in the Hydrologic Cycle 7. O in Minerals and Rocks 8. C and Carbon Cycling 9. N Cycling in Watersheds 10.S and the Sulfur Cycle 11. Chlorine and Bromine Isotopes 12. Light Lithophile Elements: δLi and δB Glos...

I n t r o d u c t i o n : The study of Ag isotopic compositions is of particular interest because of the extinct radionuclide Pd, which decays to Ag with a half-life of 6.5 Myrs. This chronometer has been successfully applied to unravel formation and differentiation processes of iron meteorites [1-3]. Compared to the early measurements by TIMS, the use of multi-collector inductively coupled pla...