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

摘要

Antarctic ice core nitrate (NO 3 - ) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO 3 - 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 NO 3 - concentrations in the snow in different environments. Results show that an increasing trend of NO 3 - concentrations with distance inland is present in surface snow, and NO 3 - is extremely enriched in the topmost crystal ice (with a maximum of 16.1 μ eq?L sup?1/sup) . NO 3 - concentration profiles for snow pits vary between coastal and inland sites. On the coast, the deposited NO 3 - was largely preserved, and the archived NO 3 - fluxes are dominated by snow accumulation. The relationship between the archived NO 3 - and snow accumulation rate can be depicted well by a linear model, suggesting a homogeneity of atmospheric NO 3 - levels. It is estimated that dry deposition contributes 27–44?% of the archived NO 3 - fluxes, and the dry deposition velocity and scavenging ratio for NO 3 - were relatively constant near the coast. Compared to the coast, the inland snow shows a relatively weak correlation between archived NO 3 - and snow accumulation, and the archived NO 3 - fluxes were more dependent on concentration. The relationship between NO 3 - and coexisting ions (nssSO 4 2 - , Na sup+/sup and Cl sup?/sup) was also investigated, and the results show a correlation between nssSO 4 2 - (fine aerosol particles) and NO 3 - in surface snow, while the correlation between NO 3 - and Na sup+/sup (mainly associated with coarse aerosol particles) is not significant. In inland snow, there were no significant relationships found between NO 3 - and the coexisting ions, suggesting a dominant role of NO 3 - recycling in determining the concentrations.