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

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 (delta N-15, delta O-18, and Delta O-17) in snow in central Antarctica, Dome A. In the upper similar to 90 cm snowpack, variations in concentration and isotopic composition of NO3- are dominated by photolytic loss, and delta O-18 and Delta O-17 of NO3- are associated with the recycling of NOx to NO3- in the condensed phase driven by photolysis. In the deeper snowpack (similar to 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.

Automated summary

The interpretation of NO3- variability recorded in ice cores is challenging due to its potential loss from snow. This study presents 60-year records of NO3- and its isotopic composition in snow in central Antarctica, revealing the dominant role of photolytic loss in the variations of NO3- concentrations and isotopic composition. The authors also find that the prolonged trends in NO3- and its isotopes in deeper snowpacks coincide with the long-term decrease in total column ozone, suggesting enhanced snow NO3- photolysis.