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

Guitao Shi,Yuansheng Li,Jinhai Yu,Su Jiang,Meredith G Hastings,Hongmei Ma,Zhengyi Hu,Chuanjin Li,Chunlei An,Tianming Ma

doi:10.5194/tc-12-1177-2018

Abstract

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.

Highlights

As the major sink of atmospheric nitrogen oxides (NOx = NO and NO2), nitrate (NO−3 ) is one of the major chemical species measured in polar snow and ice
The relationship between NO−3 and coexisting ions was investigated, and the results show a correlation between nssSO24− and NO−3 in surface snow, while the correlation between NO−3 and Na+ is not significant
NO−3 levels are thought to be linked with snow accumulation rate, and higher values are usually present in areas with low accumulation, e.g., East Antarctic plateaus (Qin et al, 1992; Erbland et al, 2013; Traversi et al, 2017)

Summary

Introduction

As the major sink of atmospheric nitrogen oxides (NOx = NO and NO2), nitrate (NO−3 ) is one of the major chemical species measured in polar snow and ice. The measurements of NO−3 in ice cores may offer potential for under-. At Halley station in coastal Antarctica, significant concentrations of organic nitrates (peroxyacetyl nitrate (PAN) and alkyl NO−3 ) were observed in the lower atmosphere (Jones et al, 2011). Not a direct source of snowpack nitrate, organic nitrates could act as source of NOx to coastal Antarctica that would contribute to NO−3 within the snowpack (Jones et al, 2011)

Methods

Results

Conclusion