HR: 14:40h
AN: A13F-04    [Abstracts]
TI: Isotopic Analysis of Nitrate in South Pole Snow and Air
AU: * McCabe, J R
EM: jmccabe@ucsd.edu
AF: UC San Diego, Dept of Chem and Biochem 9500 Gilman Dr 0356, La Jolla, CA 92093-0356 United States
AU: Savarino, J
EM: savarino@lgge.obs.ujf-grenoble.fr
AF: LGGE, 54 rue Moliere, BP 96 , St Martin d Heres, 38 402 France
AU: Thiemens, M H
EM: mht@chem.ucsd.edu
AF: UC San Diego, Dept of Chem and Biochem 9500 Gilman Dr 0356, La Jolla, CA 92093-0356 United States
AB: Nitrate is a major component of polar snow as a result of atmospheric deposition. In the atmosphere, OH and O₃ control nitrate formation. Therefore, observations of nitrate in polar snow could provide clues to long-term changes in the global oxidation capacity by revealing changes in the short-lived species controlling its formation. While the interpretation of nitrate in snow has proven elusive due to effects from post-depositional processes, the presence of mass independent oxygen isotopic composition in nitrate may provide a means to elucidate the role of oxidants and post-depositional processes. Isotopic analysis of nitrate from a 6 meter snow pit at South Pole suggest the role of post-depositional processing and is compared to instrumental records of surface ozone, total column ozone and surface UV irradiance. Surface nitrate concentrations reached up to 422 ppb while the isotopic values also saw a dramatic rise in the top 10 cm to 33 ‰ that was 8 ‰ higher than the average isotopic composition at depth (25. 7 ‰). This result implicates the role of photochemistry, which has been shown to reduce Δ ¹⁷O -NO₃ upon photolysis (McCabe et al. 2005). Below the surface, Δ ¹⁷O -NO₃ exhibits a three-year cycle that has no clear explanation at this time. When considered along with fluctuations in UV and total column ozone, there is no direct correlation. A yearlong record of nitrate aerosol and surface snow will also be measured to investigate if the isotopic composition of atmospheric nitrate is reflected in the snowpack.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0736 Snow (1827, 1863)
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005