N2O production and cycling within Antarctic sea ice

Nitrous oxide (N2O) is a potent greenhouse gas that has a lifetime of 114 years in the atmosphere
and a global warming potential 300 time higher than that of CO2. However there are still large
uncertainties and gaps in the understanding of the N2O cycle in polar oceans and particularly
associated to sea ice. Sources and sinks of N2O are therefore poorly quantified. To date, only one
study by Randall et al. 2012 present N2O measurements in sea ice. They pointed out that sea ice
formation and melt has the potential to generate sea-air or air-sea fluxes of N2O, respectively. The
main processes (except the transport processes) involved in the N2O cycle within the aquatic
environment are nitrification and denitrification. Recent observations of significant nitrification in
Antarctic sea ice shed a new light on nitrogen cycle within sea ice. It has been suggested that
nitrification supplies up to 70% of nitrate assimilated within Antarctic spring sea ice. Corollary,
production of N2O, a by-product of nitrification, can potentially be significant. Our recent studies in
Antarctic land fast ice in McMurdo Sound, confirmed this suggestion, where N2O release to the
atmosphere was estimated to reach 4µmol.m-2.yr-1. But this assessment is probably an
underestimation since it only accounts for dissolved N2O while a significant amount of N2O is likely
to occur in the gaseous form like N2, O2 and Ar. We will then address the new tools to measure the
bulk concentration of N2O (dissolved and gaseous) in sea ice, and the production of N2O by
sympagic microorganisms - what process is dominant and how much N2O is produced - based on
the first time series of N2O measurement in sea ice. The determination of the isotopic composition
of N2O using cavity enhanced laser absorption spectroscopy technique (Off-axis ICOS) will allow us
to determine the origin of these processes.