- 1Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland (lison.soussaintjean@unibe.ch)
- 2CNRS - IRD - INRAE - Grenoble INP - IGE, Université Grenoble Alpes, Grenoble, France
- 3Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
- 4Environmental Research Unit, Commonwealth Scientific and Industrial Research Organisation, Aspendale, Victoria, Australia
- 5College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, USA
- 6Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands
Nitrous oxide (N2O) is a potent greenhouse gas also involved in the destruction of stratospheric ozone. Unlike carbon dioxide (CO2) and methane (CH4), there is no continuous record of past atmospheric concentrations of N2O from ice cores over the last 800,000 years. This is due to the production of excess N2O in dust-rich Antarctic ice during glacial periods.
We investigated the production of N2O that happens in the ice sheet - referred to as in situ production - with the aim of systematically identifying affected ice core samples. To this end, we measured the nitrogen bulk and position-specific isotopic composition of N2O in dust-rich samples affected by in situ production in the EDC, Vostok, EDML, and Taylor Glacier ice cores. We calculated the isotopic signature of in situ-produced N2O with a mass balance approach. For this calculation, we had to determine the amount of N2O enrichment from in situ production relative to an unaffected atmospheric baseline for N2O concentration and isotopic composition. We chose to use as the atmospheric baseline the N2O record from the TALDICE ice core, which has a low dust content and is supposed to be the least affected by in situ production. To investigate a potential nitrogen precursor, we then compared the nitrogen isotopic signature of in situ-produced N2O with that of nitrate (NO3-) measured in the same samples.
These measurements reveal that the isotopic composition of the central-position N atom in the N2O molecule (δ15Nα) correlates with the nitrogen isotopic composition of NO3- with a slope of 1. However, there is no correlation between the nitrogen isotopic composition of the terminal-position N atom in N2O (δ15Nβ) and that of NO3-. Therefore, our study shows that the N2O produced in situ is hybrid, i.e., the two N atoms in the N2O molecule come from two distinct nitrogen sources. Our hypothesis is based on a reaction involving three reactants. NO3- present in the ice provides the central-position N atom in N2O. It is first converted to NO2- by a reducing species contained in the dust (e.g. Fe2+), and NO2- reacts with a yet unknown nucleophilic species that is the source of the terminal-position N atom.
How to cite: Soussaintjean, L., Schmitt, J., Savarino, J., Menking, A., Brook, E., Seth, B., Röckmann, T., and Fischer, H.: Towards understanding the N2O production in dust-rich Antarctic ice using bulk and position-specific isotope analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8910, https://doi.org/10.5194/egusphere-egu25-8910, 2025.
