HR: 1340h
AN: A53B-1140    [Abstracts]
TI: Nitrogen and triple oxygen isotopic composition of nitrate in surface snow in Antarctica.
AU: Frey, M M
EM: markus.frey@lgge.obs.ujf-grenoble.fr
AF: LGGE, CNRS-UJF Grenoble, Saint Martin d'Heres, 38400, France
AU: Frey, M M
EM: markus.frey@lgge.obs.ujf-grenoble.fr
AF: School of Engineering, University of California, Merced, Atwater, CA 95301, United States
AU: * Morin, S
EM: samuel.morin@lgge.obs.ujf-grenoble.fr
AF: LGGE, CNRS-UJF Grenoble, Saint Martin d'Heres, 38400, France
AU: Martins, J
EM: jean.martins@hmg.inpg.fr
AF: LTHE, CNRS-UJF Grenoble, Saint Martin d'Heres, 38400, France
AU: Savarino, J
EM: joel.savarino@lgge.obs.ujf-grenoble.fr
AF: LGGE, CNRS-UJF Grenoble, Saint Martin d'Heres, 38400, France
AB: Interactions between the chemical state of the atmosphere and climate are poorly documented mainly due to the lack of a suitable set of proxies for the past atmospheric oxidation capacity, which controls the chemical lifetime of greenhouse gases such as methane or ozone. For example, to date no quantitative relationship exists between nitrate (NO₃^-) preserved in polar snow, firn and ice and atmospheric nitrogen oxides (NO_x = NO + NO₂), which are key in modulating the burden of atmospheric oxidants. This is in part due to post- depositional processing taking place in the upper snow pack altering nitrate concentrations significantly. However, the stable isotopic composition of NO₃^- potentially provides a powerful tool to not only gain insight into post-depositional processes but also to assess past ozone chemistry and major NO₃^- sinks and sources. Here we report results from the first simultaneous determination of the nitrate ¹⁵N/¹⁴N, ¹⁸O/¹⁶O and ¹⁷O/¹⁶O isotopic ratios in Antarctic surface snow samples collected on a summer traverse between Dome Concordia (75°S) and Dumont d'Urville (DDU) (66°S). Reproducible isotopic ratios were achieved using the bacterial denitrifier method and an automated on-line GC- IRMS system. The observed mean NO₃^- oxygen isotopic anomaly (Δ¹⁷O = δ¹⁷O - 0.52 δ¹⁸O) of 28.8±2.2 ‰ is consistent with the expected anomaly transfer from atmospheric ozone through HO_x-NO_x gas phase chemistry. The spatial variability of the δ¹⁵N isotopic signature allows a clear distinction between near coastal (-8.6 to -5.6 ‰) and continental high elevation sites (31-47 ‰). Inland δ¹⁵N enrichment and depleted levels near the coast support the idea of significant continental snow reemissions of nitrate and transport towards lower latitudes.
DE: 0365 Troposphere: composition and chemistry
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0736 Snow (1827, 1863)
DE: 9310 Antarctica (4207)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting