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The Molybdenum Isotopic Composition of the Modern Ocean,2013-II

The average isotope composition in delta Mo-A/95 (relative to a Johnson Mo standard solution) was as follows: delta Mo-92/95 = -2.54 +/- 0.16 parts per thousand (2SD), delta Mo-94/95 = -0.73 +/- 0.19 parts per thousand, delta Mo-96/95 = 0.85 +/- 0.07 parts per thousand, delta Mo-97/95 = 1.68 +/- 0.08 parts per thousand, delta Mo-98/95 = 2.48 +/- 0.10 parts per thousand, and delta Mo-100/95 = 4.07 +/- 0.18 parts per thousand.
 
The delta values showed an excellent linear correlation with atomic mass of Mo-A (R-2 = 0.999). Three-isotope plots for the Mo isotopes were fitted with straight lines whose slopes agreed with theoretical values for mass-dependent isotope fractionation. These results demonstrate that Mo isotopes are both uniformly distributed and follow a mass-dependent fractionation law in the modern oxic ocean.

In addition, Mo isotopic analysis revealed that delta Mo-98/95 of the standard used in this study was 0.117 +/- 0.009 parts per thousand lighter than the Mo standard that was used by Archer and Vance . A common Mo standard is urgently required for the precise comparison of Mo isotopic compositions measured in different laboratories. On the other hand, our results strongly support the possibility of seawater as an international reference material for Mo isotopic composition.

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