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 (nssSO42−, Na+ and Cl−) was also investigated, and the results show a correlation between nssSO42− (fine aerosol particles) and NO3− in surface snow, while the correlation between NO3− and Na+ (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.