The preservation of atmospheric nitrate in snow at Summit, Greenland



[1] There is great interest in using nitrate (NO3) isotopic composition in ice cores to track the history of precursor nitrogen oxides (NOx = NO + NO2) in the atmosphere. NO3, however, can be lost from the snow by surface processes, such as photolysis back to NOx upon exposure to sunlight, making it difficult to interpret records of NO3 as a tracer of atmospheric NOx loading. In a campaign consisting of two field seasons (May–June) at Summit, Greenland, high temporal frequency surface snow samples were collected and analyzed for the oxygen isotopic composition of NO3. The strong, linear relationship observed between the oxygen isotopes of NO3, in both 2010 and 2011, is difficult to explain in the presence of significant postdepositional processing of NO3, unless several unrelated variables change in concert. Therefore, the isotopic signature of NO3 in the snow at Summit is most feasibly explained as preserved atmospheric NO3 deposition.