Deposition, recycling, and archival of nitrate stable isotopes between the air–snow interface: comparison between Dronning Maud Land and Dome C, Antarctica

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Winton, V. Holly L., Ming, Alison, Caillon, Nicolas, Hauge, Lisa, Jones, Anna, Savarino, Joel, Yang, Xin, Frey, Markus
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Antarctic; Dronning Maud Land; East Antarctica; Kohnen; Kohnen Station; Antarc*; Antarctica; DML; ice core
• Online Access: https://hal.science/hal-03402284; https://hal.science/hal-03402284/document; https://hal.science/hal-03402284/file/Winton-2020.pdf; https://doi.org/10.5194/acp-20-5861-2020

International audience Abstract. The nitrogen stable isotopic composition in nitrate (δ15N-NO3-) measured in ice cores from low-snow-accumulation regions in East Antarctica has the potential to provide constraints on past ultraviolet (UV) radiation and thereby total column ozone (TCO) due to the sensitivity of nitrate (NO3-) photolysis to UV radiation. However, understanding the transfer of reactive nitrogen at the air–snow interface in polar regions is paramount for the interpretation of ice core records of δ15N-NO3- and NO3- mass concentrations. As NO3- undergoes a number of post-depositional processes before it is archived in ice cores, site-specific observations of δ15N-NO3- and air–snow transfer modelling are necessary to understand and quantify the complex photochemical processes at play. As part of the Isotopic Constraints on Past Ozone Layer Thickness in Polar Ice (ISOL-ICE) project, we report new measurements of NO3- mass concentration and δ15N-NO3- in the atmosphere, skin layer (operationally defined as the top 5 mm of the snowpack), and snow pit depth profiles at Kohnen Station, Dronning Maud Land (DML), Antarctica. We compare the results to previous studies and new data, presented here, from Dome C on the East Antarctic Plateau. Additionally, we apply the conceptual 1D model of TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) to assess the impact of NO3- recycling on δ15N-NO3- and NO3- mass concentrations archived in snow and firn. We find clear evidence of NO3- photolysis at DML and confirmation of previous theoretical, field, and laboratory studies that UV photolysis is driving NO3- recycling and redistribution at DML. Firstly, strong denitrification of the snowpack is observed through the δ15N-NO3- signature, which evolves from the enriched snowpack (−3 ‰ to 100 ‰), to the skin layer (−20 ‰ to 3 ‰), to the depleted atmosphere (−50 ‰ to −20 ‰), corresponding to mass loss of NO3- from the snowpack. Based on the TRANSITS model, we find that NO3- is recycled two times, on ...