Preprints
https://doi.org/10.5194/tc-2021-92
https://doi.org/10.5194/tc-2021-92

  12 Apr 2021

12 Apr 2021

Review status: this preprint is currently under review for the journal TC.

Impacts of the photo-driven post-depositional processing on snow nitrate and its isotopes at Summit, Greenland: a model-based study

Zhuang Jiang1, Becky Alexander2, Joel Savarino3, Joseph Erbland3, and Lei Geng1,4,5,6 Zhuang Jiang et al.
  • 1Anhui Province Key Laboratory of Polar Environment and Global Change, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China
  • 2Department of Atmospheric Sciences, University of Washington, Seattle WA, USA
  • 3Univ. Grenoble Alpes, CNRS, IRD, G-INP, Institut des Géosciences de l’Environnement, Grenoble, France
  • 4Laboratory for Ocean Dynamics and Climate, Pilot Qingdao National Laboratory for Marine Science and Technology, Qingdao, Shandong, China
  • 5CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui, China
  • 6Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, China

Abstract. Atmospheric information embedded in ice-core nitrate is disturbed by post-depositional processing. Here we used a layered snow photochemical column model to explicitly investigate the effects of post-depositional processing on snow nitrate and its isotopes (δ15N and Δ17O) at Summit, Greenland where post-depositional processing was thought to be minimal due to the high snow accumulation rate. We found significant redistribution of nitrate in the upper snowpack through photolysis and up to 21 % of nitrate was lost and/or redistributed after deposition. The model indicates post-depositional processing can reproduce much of the observed δ15N seasonality, while seasonal variations in δ15N of primary nitrate is needed to reconcile the timing of the lowest seasonal δ15N. In contrast, post-depositional processing can only induce less than 2.1 ‰ seasonal Δ17O change, much smaller than the observation (9 ‰) that is ultimately determined by seasonal differences in nitrate formation pathway. Despite significant redistribution of snow nitrate in the photic zone and the associated effects on δ15N seasonality, the net annual effect of post-depositional processing is relatively small, suggesting preservation of atmospheric signals at the annual scale under the present Summit conditions. But at longer timescales when large changes in snow accumulation rate occurs this post-depositional processing could become a major driver of the δ15N variability in ice core nitrate.

Zhuang Jiang et al.

Status: open (until 07 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-92', Anonymous Referee #1, 16 Apr 2021 reply
  • RC2: 'Review report', Anonymous Referee #2, 11 May 2021 reply

Zhuang Jiang et al.

Zhuang Jiang et al.

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Short summary
We used a snow photochemmistry model (TRANSITS) to simulate the seasonal nitrate snow profile at Summit, Greenland. Comparisons between model outputs and observations suggest that at Summit post-depositional processing is active and probably dominates the snowpack δ15N seasonality. We also used the model to assess the degree of snow nitrate loss and the consequences in its isotopes at present and in the past, which helps for quantatively interpretation of ice core nitrate record.