Nitrate deposition and preservation in the snowpack along a traverse from coast to the ice sheet summit (Dome A) in East Antarctica

Abstract

Antarctic ice core nitrate (NO3 ) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO3 at the ice sheet surface must first be understood. Therefore, an intensive program of snow and atmospheric sampling was made on a traverse from the coast to the ice sheet summit, Dome A, East Antarctica. Snow samples in this observation include 120 surface snow samples (top ~ 3 cm), 20 snow pits with depths of 150 to 300 cm, and 6 crystal ice samples (the topmost needle-like layer on Dome A plateau). The main purpose of this investigation is to characterize the distribution pattern and preservation of NO3 concentrations in the snow in different environments. Results show that an increasing trend of NO3 concentrations with distance inland is present in surface snow, and NO3 is extremely enriched in the topmost crystal ice (with a maximum of 16.1 μeq L-1/NO3 concentration profiles for snow pits vary between coastal and inland sites. On the coast, the deposited NO3 was largely preserved, and the archived NO3 fluxes are dominated by snow accumulation. The relationship between the archived NO3- and snow accumulation rate can be depicted well by a linear model, suggesting a homogeneity of atmospheric NO3- levels. It is estimated that dry deposition contributes 27-44% of the archived NO3 fluxes, and the dry deposition velocity and scavenging ratio for NO3 were relatively constant near the coast. Compared to the coast, the inland snow shows a relatively weak correlation between archived NO3 and snow accumulation, and the archived NO3 fluxes were more dependent on concentration. The relationship between NO3 and coexisting ions (nssSO24, NaC and Cl-1 was also investigated, and the results show a correlation between nssSO24 (fine aerosol particles) and NO3 in surface snow, while the correlation between NO3 and NaC (mainly associated with coarse aerosol particles) is not significant. In inland snow, there were no significant relationships found between NO3 and the coexisting ions, suggesting a dominant role of NO3 recycling in determining the concentrations.