Year-round records of the ionic composition of Antarctic aerosol were obtained at the inland Dome C (DC) and coastal Neumayer (NM) sites, with additional observations of black carbon at NM. Discussions focus on the origin of ammonium in Antarctica. This first Antarctic atmospheric study of several species emitted by biomass burning indicates that black carbon, oxalate, and fine potassium reach a maximum in October in relation to biomass burning activity in the southern hemisphere. Ammonium reaches a maximum two months later, suggesting that biomass burning remains a minor ammonium source there. The ammonium maximum in December coincides with the occurrence of diatom blooms in the austral ocean, suggesting that oceanic ammonia emissions are the main source of ammonium in Antarctica. The ammonium to sulfur-derived biogenic species molar ratio of 0.15 in summer suggests far lower ammonia emissions from the polar ocean than mid-latitude southern oceans.