Air–snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records

• Published in: Atmospheric Chemistry and Physics
• Main Authors: J. Erbland, J. Savarino, S. Morin, J. L. France, M. M. Frey, M. D. King
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; East Antarctica; The Antarctic; Antarc*; Antarctica; ice core
• Online Access: https://doi.org/10.5194/acp-15-12079-2015; https://doaj.org/article/6eec67ac0844481a965a732cd3404f7a

Unraveling the modern budget of reactive nitrogen on the Antarctic Plateau is critical for the interpretation of ice-core records of nitrate. This requires accounting for nitrate recycling processes occurring in near-surface snow and the overlying atmospheric boundary layer. Not only concentration measurements but also isotopic ratios of nitrogen and oxygen in nitrate provide constraints on the processes at play. However, due to the large number of intertwined chemical and physical phenomena involved, numerical modeling is required to test hypotheses in a quantitative manner. Here we introduce the model TRANSITS (TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow), a novel conceptual, multi-layer and one-dimensional model representing the impact of processes operating on nitrate at the air–snow interface on the East Antarctic Plateau, in terms of concentrations (mass fraction) and nitrogen (δ 15 N) and oxygen isotopic composition ( 17 O excess, Δ 17 O) in nitrate. At the air–snow interface at Dome C (DC; 75° 06' S, 123° 19' E), the model reproduces well the values of δ 15 N in atmospheric and surface snow (skin layer) nitrate as well as in the δ 15 N profile in DC snow, including the observed extraordinary high positive values (around +300 ‰) below 2 cm. The model also captures the observed variability in nitrate mass fraction in the snow. While oxygen data are qualitatively reproduced at the air–snow interface at DC and in East Antarctica, the simulated Δ 17 O values underestimate the observed Δ 17 O values by several per mill. This is explained by the simplifications made in the description of the atmospheric cycling and oxidation of NO 2 as well as by our lack of understanding of the NO x chemistry at Dome C. The model reproduces well the sensitivity of δ 15 N, Δ 17 O and the apparent fractionation constants ( 15 ε app , 17 E app ) to the snow accumulation rate. Building on this development, we propose a framework for the interpretation of nitrate records measured from ice cores. Measurement of ...