Polar ice cores contain long and detailed records of paleoatmospheric composition, paleoclimate, and their evolution through time. By making a complete ionic balance in melted samples of ice, it is possible to evaluate the origin (identification of chemical compounds) and sources (continental, marine, volcanic, extraterrestrial) of soluble impurities contained in these ice cores. Once these are known, an attempt can be made to try and explain the cause of any observed changes. In this paper we present results of analyses of the major soluble impurities (H+, Na+, NH4+, K+, So4-, NO3-, Cl-) made on bulk samples selected at approximately 50 m intervals down the length of an ice core from Byrd Station, Antarctics (80¿01'S, 119¿31'W, 1530 m). Most samples are in ionic balance, and it is therefore possible to suggest with which compounds the ionic impurities are linked. These compounds include an important contribution from both sea salts (NaCl and Na2SO4) and strong acids (approximately equal amounts of HNO3 and H2SO4). The Cl/Na mole ratio is found to be quite stable throughout the core and hovers about the expected bulk sea water ratio. In general, the marine-derived components at Byrd Station decreased by a factor of 2 between the Late Glacial Maximum and Holocene while the gas-derived acid components decreased by a factor of only 1.5. Some possible causes of these variations are suggested.