Laboratory experiments were done to better understand the electrical conduction mechanisms of impure, polycrystalline ice as represented by the 2503 m Dome Fuji (Antarctica) ice core. Also, two electrical measurement techniques for ice cores were compared and their usefulness for determining the acidity of ice cores was studied. We measured the electrical conductivity and complex permittivity of 167 slab-ice samples at frequencies from 20 Hz to 1 MHz. Measurements were performed at –21˚C for all samples, and at –110˚ to –20˚C for several samples, to examine the effects of temperature. We found linear relations between the AC loss factor and the molarity of sulfuric acid, and between the high-frequency-limit conductivity and the AC loss factor. Thus, the acidity levels can be determined from the AC loss factor. In contrast, the electrical conductivity measurement (ECM) current correlated weakly with the other parameters; furthermore, the correlation worsens at larger signal. In several samples containing high acidity, the dielectric properties had distinct changes near –81˚C. We argue that these changes were caused by a change from a liquid-vein-mediated conduction mechanism above the eutectic point of the solute/water/ ice system to a solid-phase conduction mechanism at lower temperatures.

The 320 kyr climatic record from the 2503 m Dome Fuji (Antarctica) ice core was analyzed using two electrical methods: AC-ECM and ECM (electrical conductivity measurements). AC-ECM is a method to detect the complex admittance between electrodes dragged on the ice surface with mm-scale resolution and uses 1V and 1 MHz. the ratio of the real to imaginary part of the admittance is the AC loss factor, which responds linearly to the amount of sulfuric acid and hydrogen ions. Both the AC loss factor and the ECM current respond to acid, but the ECM signal tends to saturate at high acidities. Dome Fuji ice was measured to be highly acidic, with background values of 2–7 μM, and had 4500 major peaks with acidities of up to 90 μM. This ice-core evidence and earlier snow-chemistry survey around the dome region indicates that Dome F may have a better connection to the stratosphere than have sites at lower altitude, which allows more stratospheric aerosol and gases to reach the snow surface. Acidity tends to be high in interglacial periods, but correlation between acidity and δ18O is not straightforward. Electrical signals decreased and smoothed out with increasing depth; the diffusion coefficients deduced from this smoothing were 10–102 times greater than in solid ice. the ice core exhibited electromechanical effects and expelling effects from sulfate peaks.

Thermodynamic calculations of the reaction between hydrated OPC phases and saline groundwater indicate an elevated pH > 13, which is not associated with the well known initial release of the alkalis. Instead, the pH elevation is attributed to the generation of OH− accompanied with the precipitation of Friedel's salt (Ca3Al2O6·CaCl2·10H2O; AFm-Cl2) from the reaction of portlandite (Ca(OH)2;CH) and hydrogarnet (Ca3Al2O6·6H2O; C3AH6) with chloride ions from the saline groundwater. If such a reaction mechanism were to occur in the context of the geological disposal of radioactive wastes, the impact of a hyper alkaline plume on other barrier components, such as a bentonite buffer, could be significant. Experimental investigations were therefore conducted using only portlandite and hydrogarnet to represent hydrated OPC and NaCl solution to represent a saline groundwater. The pH elevation was confirmed and showed good agreement with the thermodynamic calculations. The experiments were repeated using hardened OPC paste to confirm this reaction mechanism in the presence of other hydrated OPC phases. In this case, however, the pH elevation was not as high as expected. This deviation can be explained by the residual aluminum, after being partially consumed by AFt and/or AFm, not being wholly assigned to hydrogarnet and a better agreement between the thermodynamic calculations and the experimentally measured results can be made assuming a fraction of aluminum is incorporated into the C-S-H gel phase.