On the potential fingerprint of the Antarctic ozone hole in ice-core nitrate isotopes: a case study based on a South Pole ice core

Column ozone variability has important implications for surface photochemistry and the climate. Ice-core nitrate isotopes are suspected to be influenced by column ozone variability and delta N-15(NO3-) has been sought to serve as a proxy of column ozone variability. In this study, we examined the ability of ice-core nitrate isotopes to reflect column ozone variability by measuring delta N-15(NO3-) and Delta O-17(NO3-) in a shallow ice core drilled at the South Pole. The ice core covers the period 1944-2005, and during this period delta N-15(NO3-) showed large annual variability ((59.2 +/- 29.3)parts per thousand), but with no apparent response to the Antarctic ozone hole. Utilizing a snow photochemical model, we estimated 6.9 parts per thousand additional enrichments in delta N-15(NO3-) could be caused by the development of the ozone hole. Nevertheless, this enrichment is small and masked by the effects of the snow accumulation rate at the South Pole over the same period of the ozone hole. The Delta O-17(NO3-) record has displayed a decreasing trend by similar to 3.4 parts per thousand since 1976. This magnitude of change cannot be caused by enhanced post-depositional processing related to the ozone hole. Instead, the Delta O-17(NO3-) decrease was more likely due to the proposed decreases in the O-3 / HOx ratio in the extratropical Southern Hemisphere. Our results suggest ice-core delta N-15(NO3-) is more sensitive to snow accumulation rate than to column ozone, but at sites with a relatively constant snow accumulation rate, information of column ozone variability embedded in delta N-15(NO3-) should be retrievable.