Snow Nitrate Isotopes in Central Antarctica Record the Prolonged Period of Stratospheric Ozone Depletion From ∼1960 to 2000

• Published in: Geophysical research letters 2022-07, Vol.49 (13), p.n/a
• Main Authors: Shi, Guitao, Hu, Ye, Ma, Hongmei, Jiang, Su, Chen, Zhenlou, Hu, Zhengyi, An, Chunlei, Sun, Bo, Hastings, Meredith G.
• Format: Article
• Language: English
• Subjects: Accumulation; Antarctic ozone; central Antarctica; Chemical composition; Cores; Domes; Ice; ice core nitrate; Ice cores; Ice formation; Isotope composition; Isotopes; Nitrates; nitrogen and oxygen isotopes; Nitrogen compounds; Oxides; Oxygen; Oxygen isotopes; Ozone; Ozone depletion; Ozone variations; Paleoclimate; Photolysis; Records; Snow; Snow accumulation; Snowpack; Solar radiation; Solar ultraviolet radiation; stratospheric ozone depletion; Trends; Ultraviolet radiation; Variability; Variation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL098986

Interpretation of NO3− variability recorded in ice cores remains challenging as it can be lost from snow. Here, we present 60‐year records of NO3− and its isotopic composition (δ15N, δ18O, and Δ17O) in snow in central Antarctica, Dome A. In the upper ∼90 cm snowpack, variations in concentration and isotopic composition of NO3− are dominated by photolytic loss, and δ18O and Δ17O of NO3− are associated with the recycling of NOx to NO3− in the condensed phase driven by photolysis. In the deeper snowpack (∼1960–2000), we observe prolonged trends in concentration and isotopic composition of NO3−, which are best explained as enhanced snow NO3− photolysis due to long‐term decreasing total column ozone (TCO). That is, the prolonged period of trends in NO3− and its isotopes in extremely low snow accumulation sites such as Dome A relay information on variations in TCO and consequently surface solar ultraviolet radiation over time. Plain Language Summary The atmospheric information contained in polar snow/ice nitrate (NO3−) is of great interest in paleoclimate research. The interpretation of NO3− variability recorded in ice cores, however, remains challenging as atmospheric NO3− can be lost from snow prior to ice formation. Here, we present 60‐year records of NO3− and its isotopic composition in snow pits collected from Dome A, an exceptionally low snow accumulation site in central Antarctica. Analysis of our data shows that variations in concentration and isotopic composition of NO3− in the upper snowpack are dominated by photolytic loss, resulting in distinct trends in nitrogen and oxygen isotopes of NO3−. In the deeper snowpack, we observe clear trends in both concentration and isotopic composition of NO3−, which are closely associated with enhanced snow NO3− UV photolysis due to the decreasing stratospheric ozone during ∼1960–2000. That is, elevated UV doses reaching the snow surface as a result of larger Antarctic ozone holes significantly promoted snow NO3− photolysis. These findings raise the prospect of better understanding of past stratospheric ozone variations using ice core NO3− isotope records. Key Points Condensed phase NO3− reformation in snow driven by photolysis is recorded in δ18O and Δ17O Clear trends in NO3− and its isotopes from ∼1960 to 2000 were related to depletion of stratospheric ozone Interannual variations in snow NO3− were dominated by local physical processes and snow chemistry