Meredith Hastings

Climate history frozen in Greenland's ice and snow

JISAO postdoc Meredith G. Hastings and graduate student Justin Wettstein collected a 100-meter ice core, surface snow and ambient air samples during a month at the summit of Greenland. Samples from each will be analyzed using a new technique to help understand nitrogen oxide sources, oxidation chemistry in the atmosphere and connections of each to climate change. The fieldwork, funded by the National Science Foundation with additional support by JISAO, is part of a project entitled "Isotopic composition of nitric acid and nitrogen oxides at Summit Greenland." Hastings and UW Associate Professor Eric J. Steig are Principal Investigators on the grant.

Nitrogen oxides are a key component of the atmosphere, but little is known about past concentrations or source changes. Nitrogen oxides directly impact the concentrations of ozone and hydroxyl radicals (OH), the main oxidants of the atmosphere. Fossil fuel burning, biomass burning, soil microbial activity, and lightning represent the largest sources of nitrogen oxides.

The major sink of nitrogen oxides from the atmosphere is nitric acid (or nitrate), a major component of acid rain and a source of biologically available nitrogen. The isotopic composition of atmospheric nitrate represents a powerful new tool for studying the sources and chemistry of nitrogen oxides. Recent research has shown that the isotopic composition of nitrate is impacted by the sources of nitrogen oxides and different chemical reaction pathways. Applying this technique to ice cores will give researchers a unique opportunity to look at variations in atmospheric chemistry, changes in the sources of nitrogen oxides, and their connections with climate change.

A primary goal of this research is to compare diurnal, seasonal and inter-annual variability in the isotopic composition of nitrate to human and climate-related changes using comparable measurements obtained from ambient air, snow and ice samples.

To interpret the record of nitrate archived in the snow and ice in Greenland, we must also distinguish the air-to-snow transfer of the isotopes, which Hastings, Steig, and co-collaborators hope to better understand with the recovered snow and air samples.

Air, snow and snowpit samples will also help to characterize the influence of post-depositional processes on snow nitrate.Analysis of the ice core should reveal the seasonal variability in the isotopic composition of nitrate over the last ~300 years, its connection to variations in the physical climate system and changes in the sources (e.g., the Industrial Revolution) and chemistry of nitric acid in the atmosphere.

A long-term record holds the hope of connecting atmospheric transport to nitrate isotope deposition via the dependencies on source region, oxidant chemistry, and long-term changes in the relative contribution of different sources (e.g., escalation of human-related deposition after the Industrial Revolution).