We have developed new methods for natural abundance isotope ratio measurement of several biologically available and typically dissolved forms of N that are common in the environment: the 15N/14N, 18O/16O, and 18O/17O/16O of nitrate, the 15N/14N of total dissolved N (i.e. dissolved organic N in waters lacking nitrate and ammonium), and the 15N/14N of ammonium. For paleoceanographic work, we developed new techniques for the 15N/14N of the microfossil-bound N of diatoms (made of opal), planktonic foraminifera (calcite), and scleractinian corals (aragonite). All of these approaches have as their cornerstone the “denitrifier” method for nitrate isotopic analysis, in which nitrate (NO3-) is converted to nitrous oxide (N2O) gas by a strain of denitrifying bacteria that lacks an active N2O reductase, followed by analysis of the product N2O with a stable isotope ratio mass spectrometer.
Coupling of the denitrifier method, which yields the 15N/14N and 18O/16O of nitrate (NO3-)(1,2), with other steps to yield the 15N/14N of dissolved organic N (DON, 3), microfossil-bound organic N (4), and dissolved ammonium (NH4+, 5). “MS” indicate mass spectrometric analysis.
References
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the…