The preservation of atmospheric nitrate in snow at Summit, Greenland

Abstract There is great interest in using nitrate (NO 3 − ) isotopic composition in ice cores to track the history of precursor nitrogen oxides (NO x = NO + NO 2 ) in the atmosphere. NO 3 − , however, can be lost from the snow by surface processes, such as photolysis back to NO x upon exposure to sunlight, making it difficult to interpret records of NO 3 − as a tracer of atmospheric NO x 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 NO 3 − . The strong, linear relationship observed between the oxygen isotopes of NO 3 − , in both 2010 and 2011, is difficult to explain in the presence of significant postdepositional processing of NO 3 − , unless several unrelated variables change in concert. Therefore, the isotopic signature of NO 3 − in the snow at Summit is most feasibly explained as preserved atmospheric NO 3 − deposition.