The chemical basis for the electrical stratigraphy of ice

Antarctic and Greenland ice core samples were studied using two different stratigraphic electrical techniques. The electrical conductivity measurement (ECM) technique is a dc method, while dielectric profiling (DEP) is an ac method. It was found that ECM responds only to acid, even in large excess of neutral salt concentrations. DEP responds to both acid and salt content of the ice. Acids may be giving rise to conduction through an increase in the number of ionisation defects, or through a network of liquid veins between ice grains. Salts on the other hand appear to give rise to Bjerrum defects, which are bound charges and cannot provide a dc current, but do produce a dielectric ac conductivity. The two methods can be used together to give a rapid prediction of both acid and salt content of cores. This may be of particular use in Wisconsin-age ice from Greenland, but can generally be used to define parts of cores worthy of detailed chemical study.