A thoroughly validated spreadsheet for calculating isotopic abundances (²H, ¹⁷O, ¹⁸O) for mixtures of waters with different isotopic compositions

Abstract

RATIONALE: Oxygen and hydrogen stable isotopes are widely used tracers for studies on naturally occurring and laboratory mixtures of isotopically different waters. Although the mixing calculations are straightforward to perform, there are ample possibilities to make mistakes, especially when dealing with a large number of mixed fluids. To facilitate isotope mixing calculations and to avoid computational mistakes, a flexible tool to carry out these calculations is in demand. METHODS: We developed, in three independent efforts, spreadsheets to carry out the mixing calculations for a combination of waters with different isotopic compositions using the isotope mass balance equation. We validated our calculations by comparison of the results of the three spreadsheets for a large number of test calculations. For all the cases, we obtained identical results down to the 12 th to 14 th significant digit. RESULTS: We present a user-friendly, thoroughly validated spreadsheet for calculating 2 H, 17 O and 18 O stable isotopic abundances and respective isotope delta values for mixtures of waters with arbitrary isotopic compositions. The spreadsheet allows the mixing of up to 10 different waters, of which up to five can be specified using their isotopic abundances and up to five others using their isotope delta values. The spreadsheet is implemented in Microsoft Excel and is freely available from our research groups' websites. CONCLUSIONS: The present tool will be applicable in the production and characterization of singly and doubly labeled water (DLW) mother solutions, the analysis of isotope dilution measurements, the deduction of unknown isotope values of constituents for mixtures of natural waters, and many other applications. Copyright © 2015 John Wiley & Sons, Ltd.Stable isotope mixing calculations are used for studies on naturally occurring interactions between different water bodies: ground water with surface waters (river, lake, stream, wetland, or sea water), [1][2][3][4][5][6] ground water/surface water and precipitation interactions, [7][8][9][10] river and lake/ocean interactions, [11][12][13][14][15] and in addition, in laboratory applications such as the use of the isotope dilution technique, and the production of enriched and diluted mixtures for pharmaceutical and biological studies. [16][17][18][19][20] Isotopic compositions mix conservatively. The isotopic abundances of a mixture are simply related to the isotopic abundances of the isotopes in each component and the mole fraction of the individual components. While the calculations seem straightforward to perform using simple expressions, they are nevertheless complicated, with ample possibilities of making mistakes. This is especially the case when dealing with the mixing of waters of which some are specified with their isotopic abundances and others with delta values. Also, the calculations become more complex when the number of mixed fluids increases. To facilitate isotope mixing calculations and to avoid computational mistakes, we developed a flexible ...

Preliminary assessment of stable nitrogen and oxygen isotopic composition of USGS51 and USGS52 nitrous oxide reference gases and perspectives on calibration needs

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