Title Photolysis imprint in the nitrate stable isotope signal in snow and atmosphere of East Antarctica and implications for reactive nitrogen cycling
Author Frey, M.M.; Savarino, J.; Morin, S.; Erbland, J.; Martins, J.M.F.
Author Affil Frey, M.M., Université Joseph Fourier-Grenoble I, Laboratoire de Glaciologie et Géophysique de l'Environnement, St. Martin d'Heres, France. Other: British Antarctic Survey, United Kingdom
Source Atmospheric Chemistry and Physics, 9(22), p.8681-8696, . Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1680- 7316
Publication Date 2009
Notes In English. Published in Atmospheric Chemistry and Physics Discussions: 3 February 2009, http://www.atmos-chem-phys- discuss.net/9/12559/2009/acpd-9-12559-2009.ht ml; accessed in May, 2011. 70 refs. Ant. Acc. No: 91454. GeoRef Acc. No: 310119
Index Terms evaporation; experimentation; geochemistry; isotopes; oxygen isotopes; oxygen; snow; stratosphere; Antarctica--Dome C; Antarctica--East Antarctica; Greenland-- Summit; Antarctica; Arctic region; atmosphere; atmospheric transport; cycles; cyclic processes; depletion; Dome C; Dumont d'Urville; East Antarctica; enrichment; experimental studies; Greenland; ice cores; isotope fractionation; laboratory studies; mechanism; N-15; nitrate ion; nitrates; nitrogen; O-17; O-18; oxidation; photochemistry; photolysis; seasonal variations; snowpack; stable isotopes; Summit Greenland; transport; troposphere; Wilkes Land
Abstract The nitrogen (delta 15N) and triple oxygen (delta 17O and delta 18O) isotopic composition of nitrate (NO3-) was measured year-round in the atmosphere and snow pits at Dome C, Antarctica (DC, 75.1°S, 123.3°E), and in surface snow on a transect between DC and the coast. Comparison to the isotopic signal in atmospheric NO3- shows that snow NO3- is significantly enriched in delta 15N by ›200 per mil and depleted in delta 18O by ‹40 per mil. Post-depositional fractionation in Delta 17O(NO3-) is small, potentially allowing reconstruction of past shifts in tropospheric oxidation pathways from ice cores. Assuming a Rayleigh-type process we find fractionation constants #2E of -60±15 per mil, 8±2 per mil and 1±1 per mil, for delta 15N, delta 18O and Delta 17O, respectively. A photolysis model yields an upper limit for the photolytic fractionation constant 15#2E of delta 15N, consistent with lab and field measurements, and demonstrates a high sensitivity of 15#2E to the incident actinic flux spectrum. The photolytic 15#2E is process-specific and therefore applies to any snow covered location. Previously published 15#2E values are not representative for conditions at the Earth surface, but apply only to the UV lamp used in the reported experiment (Blunier et al., 2005; Jacobi et al., 2006). Depletion of oxygen stable isotopes is attributed to photolysis followed by isotopic exchange with water and hydroxyl radicals. Conversely, 15N enrichment of the NO3- fraction in the snow implies 15N depletion of emissions. Indeed, delta 15N in atmospheric NO3- shows a strong decrease from background levels (4±7 per mil) to -35 per mil in spring followed by recovery during summer, consistent with significant snowpack emissions of reactive nitrogen. Field and lab evidence therefore suggest that photolysis is an important process driving fractionation and associated NO3- loss from snow. The Delta 17O signature confirms previous coastal measurements that the peak of atmospheric NO3- in spring is of stratospheric origin. After sunrise photolysis drives then redistribution of NO3- from the snowpack photic zone to the atmosphere and a snow surface skin layer, thereby concentrating NO3- at the surface. Little NO3- appears to be exported off the EAIS plateau, still snow emissions from as far as 600 km inland can contribute to the coastal NO3- budget.
URL http://www.atmos-chem-phys.net/9/8681/2009/acp-9-8681-2009.pdf
Publication Type journal article
Record ID 65006734