Low 15N/14N ratios for nitrate in snow in the High Arctic (79°N)

We report on the 15N/14N and 18O/16O ratio analysis of nitrate in accumulated winter snowpack and fresh spring snow collected near Ny Ålesund, Svalbard (79°N), in the early summers of 2001–2003. The presence of contaminant organic matter in the silver nitrate prepared for analysis must be carefully monitored to assess its effects on δ15N, and particularly δ18O results. δ15N values ranged -18‰ to -7‰ (versus air N2) and δ18O values +60 to +85‰ (versus VSMOW). The δ18O values are in the reported range for atmospheric nitrate in other parts of the globe, and will tend to reflect the relationship between NOy oxygen and H2O+O2 in the troposphere immediately prior to nitrate deposition. δ15N values, however, are lower than those for atmospheric nitrate over most parts of the globe, but show similarities to 15N/14N ratios reported for atmospheric nitrate in the Antarctic. We discuss mechanisms for producing 15N-depleted nitrate in the troposphere, or the possibility that it reflects NOy nitrogen derived from the stratosphere.