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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D12303, doi:10.1029/2006JD007822, 2007

A record of ozone variability in South Pole Antarctic snow: Role of nitrate oxygen isotopes

Justin R. McCabe

Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, USA


Mark H. Thiemens

Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, USA


Joel Savarino

Laboratoire de Glaciologie et Geophysique de l'Environnement, CNRS, Université Joseph Fourier-Grenoble, St. Martin d'Hères, France


Abstract

The information contained in polar nitrate has been an unresolved issue for over a decade. Here we demonstrate that atmospheric nitrate's oxygen isotopic composition (Δ17O-NO3) reflects stratospheric chemistry in winter and tropospheric chemistry in summer. Surface snow isotope mass balance indicates that nitrate oxygen isotopic composition is the result of a mixture of 25% stratospheric and 75% tropospheric origin. Analysis of trends in Δ17O-NO3 in a 6 m snow pit that provides a 26-year record reveals a strong 2.70-year cycle that anticorrelates (R = −0.77) with October–November–December column ozone. The potential mechanisms linking the records are either denitrification or increased boundary layer photochemical ozone production. We suggest that the latter is dominating the observed trend and find that surface ozone and Δ17O-NO3 correlate well before 1991 (R = 0.93). After 1991, however, the records show no significant relationship, indicating an altered oxidative environment consistent with current understanding of a highly oxidizing atmosphere at the South Pole. The disappearance of seasonal Δ17O-NO3 trends in the surface layer at depth remain unresolved and demand further investigation of how postdepositional processes affect nitrate's oxygen isotope composition. Overall, the findings of this study present a new paleoclimate technique to investigate Antarctic nitrate records that appear to reflect trends in stratospheric ozone depletion by recording tropospheric surface ozone variability.

Received 24 July 2006; accepted 27 February 2007; published 16 June 2007.

Keywords: nitrate; isotopes; ozone.

Index Terms: 1041 Geochemistry: Stable isotope geochemistry (0454, 4870); 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 3344 Atmospheric Processes: Paleoclimatology (0473, 4900); 1610 Global Change: Atmosphere (0315, 0325); 0776 Cryosphere: Glaciology (1621, 1827, 1863).

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Citation: McCabe, J. R., M. H. Thiemens, and J. Savarino (2007), A record of ozone variability in South Pole Antarctic snow: Role of nitrate oxygen isotopes, J. Geophys. Res., 112, D12303, doi:10.1029/2006JD007822.