A 60-year atmospheric nitrate isotope record from a southeastern Greenland ice core with minimal postdepositional alteration

Abstract

Stable isotopes of atmospheric nitrate (NO3-) are valuable tools for tracing nitrogen sources and processes; however, their signals in ice core records are often disrupted by postdepositional processes. The ice core from the southeastern Dome (SE-Dome) in Greenland is a potential record of variations in atmospheric chemistry that has experienced a lower postdepositional effect owing to a high accumulation rate (∼1 m water equivalent per year). Herein, we report 60-year (1959–2014) δ15N(NO3-) and Δ17O(NO3-) records from the SE-Dome ice core. The δ15N(NO3-) decreased from 1960 to 1974 and exhibited clear seasonal changes (high in summer and low in winter). The Δ17O(NO3-) did not exhibit any significant long-term trends, but it did contain seasonal patterns. The mass-weighted annual average of δ15N(NO3-) values in the SE-Dome core were 4.2±2.8 ‰ lower than those in the Greenland Summit ice core between 1959 and 2006. The TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) model under the SE-Dome condition estimated changes of only 0.9 ‰ for δ15N(NO3-) and −0.2 ‰ for Δ17O(NO3-) from the initial deposition. Although differences in the source of NO3- cannot be discounted, the lower δ15N(NO3-) values observed at SE-Dome compared to Summit were likely due to reduced postdepositional alteration. Therefore, the SE-Dome ice core NO3- record offers a precise reconstruction of nitrogen oxides (NOx) emissions from both North America and western Europe, as well as atmospheric oxidation chemistry and transport, thereby providing reliable insight into atmospheric nitrogen cycling.