Dataset: Simulation of the volume-dependent changes in ẟ15N and ẟ18O for IAEA-NO3 and USGS-34 reference materials (Biological Nitrogen Isotope Fractionation project)

Sampling and analytical procedures: 


Effects of sample volume and salinity on O atom exchange with water

Given the potential influences on NO₃^- N and O isotope ratios, which include bacterial blanks, dissolved atmospheric N₂O, contaminant NO₃^- in reference materials, O atom exchange with water, and incomplete N₂O recovery and associated isotope fractionation, we attempt to reproduce the volume-dependent changes in ẟ¹⁵N and ẟ¹⁸O that we observed for IAEA-NO3 and USGS-34 reference materials.

The observed ä¹⁵N and ä¹⁸O values of N₂O for IAEA-NO3 and USGS-34 samples were referenced to that expected for IAEA-NO3 vs. the N₂O reference tank. The expected IAEA-NO3 has a ä¹⁵N of 0‰ vs. IAEA-NO3, and that expected for USGS-34 is -6.5‰ vs. IAEA-NO3. Being uncertain of the ä¹⁸O of the industrial N₂O in the reference tank, we approximate the expected ä¹⁸O value for IAEA-NO3 vs. N₂O_ref to be that observed for the highest N₂O yield (at lower aliquot volumes – which is admittedly already subject to blanks). Referenced to itself, the expected ä¹⁸O of IAEA-NO3 is 0‰ (vs. IAEA-NO3), and that for USGS-34 is -52.2‰ (vs. IAEA-NO3).

We compare the simulated ä¹⁵N and ä¹⁸O values to the observed average of 3 trials in dataset “Incidence of volume effect.”