Antarctic snow and ice contain very low concentrations of ions, <10 μmole/l Na, Cl and SO4 but these ions may play a significant part in determining the physical properties of the ice and atmospheric chemistry. At the temperatures pertaining in the Antarctic sulphuric acid would still be liquid and information on the distribution of these ions, whether they are disseminated through the crystals or concentrated in a liquid phase at the triple junctions between the crystals, is essential in order to model some of the physical properties of the ice, including electrical conductivity, rigidity and transparency to radar. Samples of 125 year old ice from the Antarctic Peninsula were planed with a sledge microtome, coated with 23 nm of Al and maintained at -160 °C in a scanning electron microscope. X-ray emission analysis of areas 1 μm square showed that S was concentrated at the triple junctions. At the temperature of the ice-sheet, -16.5 °C, the sulphuric acid would be a liquid in equilibrium with the ice at a concentration of about 2.6 mole/l but when frozen rapidly to stage temperature it would form vitreous ice at a concentration of 2.6 mole/l or it might be further concentrated to its eutectic of 4.9 mole/l. No Na or Cl were detected either at the triple junctions or elsewhere in the ice crystal. An understanding of the processes involved in the distribution and segregation of the ions, in both the atmosphere and the ice sheet, will be necessary in order to model atmospheric and ice sheet chemistry and physics.
Authors: Potts, W.T.W., Oates, K., Wolff, E.W., Mulvaney, R.