Where does the ammonium in Antarctic aerosol come from ?

Studies of ammonium (NH4+) in ice from Antarctica suggest that this species originates either from biomass fires or from oceanic emissions produced by diatoms (microscopic algae). Beyond its interest as a tracer of biogenic emissions from the Southern Ocean or biomass fires from the continents of the Southern Hemisphere, the question of the origin of NH4+ in Antarctica is important for our knowledge of the atmospheric budget of NH3 (the atmospheric precursor of NH4+). Indeed, it remains poorly understood, in particular the oceanic source, with estimates ranging from 2 to 20 teragrams of nitrogen (TgN) per year. Due to its location, Antarctica is an interesting observation site for assessing oceanic emissions.

As part of the CESOA observation service, researchers have established a climatology of atmospheric levels of NH4+, in sulfur derivatives emitted by the marine biosphere, as well as in species emitted by biomass fires, such as soot carbon and oxalate. This study, carried out on the Concordia site, was associated with the observations made at the Neumayer station. It is a coastal site not frequented by penguins which emit NH3 and oxalate by degradation of urea (nitrogenous waste that comes from the degradation of proteins by the liver), and little disturbed by carbon soot from station activities.

At Concordia and Neumayer, NH4+ peaks in December, a little before the January sulfur maximum. This is consistent with an NH3 release from diatoms in the Southern Ocean, about a month before the flowering of Phaeocystis, another species of sulfur-producing algae. In addition, Antarctic NH4+ concentrations are consistent with the lower range of oceanic NH3 emissions (2 TgN per year).

In Neumayer, soot carbon and oxalate peak in October, in relation with the South American fires. The NH4+ peak occurs later, suggesting that fires have little influence on NH4+ in Antarctica. This study therefore suggests that in addition to soot carbon, oxalate, but not NH4+, may help rebuild past fires from Antarctic ice.

Annual aerosol cycle at Neumayer (left) and Concordia (right) : Ammonium and sulfur compounds (top), oxalate (and when available soot carbon) (bottom).

To learn more :

Legrand, M., Weller, R., Preunkert, S., Jourdain, B.Retour ligne automatique
Ammonium in Antarctic aerosol : Marine biological activity versus long-range transport of biomass burning – Geophysical Research Letters
https://doi.org/10.1029/2021GL092826

Contacts :

Michel Legrand
Laboratoire inter-universitaire des systèmes atmosphériques (LISA) / IPSL
michel.legrand lisa.ipsl.fr

Suzanne Preunkert
Institut des Géosciences de l’Environnement (IGE) / OSUG
suzanne.preunkert univ-grenoble-alpes.fr

Article published on the CNRS/INSU website