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 cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by …
Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate…
Dissolved oxygen (O2) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming1,2. However, models provide an unclear picture of future ODZ…
Fossil-bound organic material holds great potential for the reconstruction of past changes in nitrogen (N) cycling. Here, with a series of laboratory experiments, we assess the potential effect of oxidative degradation, fossil dissolution, and thermal alteration on the fossil-bound N isotopic composition of different fossil types, including…
The nitrogen isotopes (δ15N) in the organic fraction of accretionary hard part structures, such as fish otoliths, may provide life histories of dietary change. We performed controlled experiments to validate the dynamics of the isotopic signal incorporation into biominerals following dietary shifts and also compared whole-otolith and serial…
For times prior to those represented by the air trapped in Antarctic ice core records, the concentration of CO2 in the atmosphere must be reconstructed using geochemical proxies. The δ13C of particulate organic carbon (POC) produced in ocean surface waters has previously been observed to covary with the concentration of CO2 in the water…
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…