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

• Published in: The Cryosphere
• Main Authors: Z. Jiang, B. Alexander, J. Savarino, J. Erbland, L. Geng
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Greenland; ice core; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-15-4207-2021; https://doaj.org/article/df85b7b45e05429db4ebf8fea9e360a3

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 ( δ 15 N and Δ 17 O ) 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 δ 15 N seasonality, while seasonal variations in δ 15 N of primary nitrate are needed to reconcile the timing of the lowest seasonal δ 15 N . In contrast, post-depositional processing can only induce less than 2.1 ‰ seasonal Δ 17 O 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 δ 15 N 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 occur this post-depositional processing could become a major driver of the δ 15 N variability in ice-core nitrate.