DOI: 10.25921/v667-1992
title: NOAA/WDS Paleoclimatology - Dome Fuji, Antarctica Core DF1 1-cm Electrical Conductivity Measurements (ECM)

description: 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 1MHz. 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 uM, and had >500 major peaks with acidities of up to 90 uM. 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 d18O 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.
description: The climatic record from the 2503m Dome Fuji (Antarctica) ice core was analyzed using AC-ECM (AC 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 1Vand 1MHz. The ratio of the real to imaginary part of the admittance is the AC loss factor (or loss tangent), which responds linearly to the amount of sulfuric acid and hydrogen ions. Dome Fuji ice was measured to be highly acidic, with background values of 2-7 micro M, and had 4500 major peaks with acidities of up to 90 micro M. Methods are as follows. After equilibrating for 1 day at the cold-room temperature at Dome F, all core sections, which were 93mm in diameter and about 1.7 m long, were cut parallel to their central axes into 60% and 40% portions by volume. The cut surfaces of the 60 % portions were further finished with a microtome knife to make fresh, smooth surfaces. Immediately after a surface was cut and finished, two AC-ECM electrodes were dragged along the surface with a 1 MHz frequency, 1 V signal. The entire ice core from depths of 112.65 to 2503.07m was covered by the measurements. However, quality of the measurement below 2251.4 m was not good. Thus, we publish here down to 2251.4 m. Although the signal was sampled every 2mm, we plot only 10mm running averages of the data to remove noise. The AC-ECM electrodes were manually dragged along the ice at about 1cm s^(-1). The AC-ECM system consists of two coaxial electrodes and an auto-balance bridge (HP model 4284A precision LCR meter). It measures the complex admittance Y= G+Bi, where G is the conductance and B is the susceptance, at the surface of ice using 1MHz to detect the high frequency-limit conductance of ice; here high-frequency limit means frequency well above the Debye dispersion only, and below the dispersions that exist above the microwave region. The electrodes were aligned perpendicular to the core axis and 15mm apart.The effective resolution of the electrodes approximately equaled the distance between the electrodes (15mm); based on a physical principle that the electrical field decreases inversely proportional to the distance from a given location to each electrode. Within this distance, about 65% of the lines of electrical force cross. Because the AC-ECM needs careful calibration of the auto-balance bridge, cable and electrodes, we calibrated the admittance to measurements on three reference materials: dry air, aluminum and Teflon. We found that insufficient calibration would double the estimated error in the AC loss factor. The AC conductance is proportional to the concentration of sulfuric acid and hydrogen ions.  All of the measured data were converted to values equivalent to -25C. For details, please see Fujita et al.(2002).