Nitrate preservation in snow at Dome A, East Antarctica from ice core concentration and isotope records

Abstract

A shallow ice core from Dome A (DA2005 ice core), East Antarctica is used to investigate the preservation and variation of nitrate (NO3−) at a location with extremely low snow accumulation rate. The average NO3− concentration of 11.8 ± 3.0 μg kg−1 in the last 2840 years covered by the top 100.42 m is the lowest in all Antarctic ice cores for this specific temporal frame. Isotopic composition of NO3− indicates that NO3− in the DA2005 core has experienced strong post-depositional processing most likely driven by photolytic chemistry, which results in the extremely low NO3− concentration. NO3− remaining at depth far below the surface is mainly cycled and produced locally. A decrease in NO3− concentration from AD 1250 to 1900 and a sustained NO3− dip in AD 1500–1900 below the long-term mean concentration may be linked with changes in primary NOx sources. In the DA2005 core, significant NO3− displacement is observed in layers containing volcanic sulphate; the degree of displacement is largely influenced by the volcanic signal magnitude, i.e., large volcanic signals lead to significant displacement, while small signals result in negligible displacement. In addition, it is found that snow accumulation rate could influence NO3− displacement by comparing DA2005 core and other Antarctic ice core records.