14 Jun 2023
 | 14 Jun 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

An inverse model to correct for the effects of post-depositional processing on ice-core nitrate and its isotopes: model framework and applications at Summit, Greenland and Dome C, Antarctica

Zhuang Jiang, Becky Alexander, Joel Savarino, and Lei Geng

Abstract. Comprehensive evaluation of the effects of post-depositional processing is a prerequisite for appropriately interpreting ice-core records of nitrate concentration and isotopes. In this study, we developed an inverse model that uses archived snow/ice-core nitrate signals to reconstruct primary nitrate flux and its isotopes (δ15N and Δ17O). The model was then applied to two polar sites, Summit, Greenland and Dome C, Antarctica using measured snowpack nitrate concentration and isotope profiles in the top few meters. At Summit, the model successfully reproduced the observed atmospheric 15δN(NO3) and Δ17O(NO3) and their seasonality. The model was also able to reasonably reproduce the observed snowpack nitrate profiles at Dome C as well as the skin layer and atmospheric δ15N(NO3) and Δ17O(NO3) at the annual scale. The calculated Fpri at Summit was 6.9 × 10-6 kgN m2 a-1 and the calculated Δ17O(NO3) of Fpri is consistent with atmospheric observations in the northern hemisphere. However, the calculated 15δN(NO3) of Fpri displays an opposite seasonal pattern to atmospheric observations in the northern mid-latitudes, but is consistent with observations in two Arctic coastal sites. The calculated Fpri at Dome C varies from 1.5 to 2.2 × 10-6 kgN m-2 a-1, with δ15N(NO3) of Fpri varying from 6.2 to 29.3 ‰ and Δ17O(NO3) of Fpri varying from 48.8 to 52.6 ‰. The calculated Fpri at Dome C is close to previous estimated stratospheric denitrification flux in Antarctica, and the high δ15N(NO3) and Δ17O(NO3) of Fpri at Dome C also point towards the dominate role of stratospheric origin of primary nitrate to Dome C.

Zhuang Jiang et al.

Status: open (extended)

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  • RC1: 'Comment on egusphere-2023-1054', Anonymous Referee #1, 27 Aug 2023 reply

Zhuang Jiang et al.

Zhuang Jiang et al.


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Short summary
Ice-core nitrate could track the past atmospheric NOx and oxidant level, but its interpretation is hampered by the post-depositional processing. In this work, an inverse model was developed and tested against two polar sites, and was shown to well reproduce the observed nitrate signals in snow and atmosphere, suggesting that the model can properly correct for the effect of post-depositional processing. This model offers a very useful tool for future studies on ice-core nitrate records.