Dome Fuji, Antarctica Core DF1 1-cm AC-ECM Data

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).本研究针对海拔2503米的南极富士圆顶（Dome Fuji）冰芯所获取的气候记录，采用交流电导测量法（AC-ECM，AC electrical conductivity measurements）开展分析。AC-ECM是一种可检测冰面拖拽电极间复导纳的毫米级分辨率检测方法，采用1V电压与1MHz频率的激励信号。复导纳的实部与虚部之比即为交流损耗因子（亦称损耗正切），其与硫酸及氢离子的含量呈线性相关关系。富士圆顶冰芯整体酸度偏高，背景酸度介于2~7微摩尔每升（μM），共识别出4500个主要酸度峰值，最高酸度可达90微摩尔每升。 具体实验流程如下：将直径93毫米、长度约1.7米的全部冰芯段，在富士圆顶冷室温度下平衡1日后，沿中心轴平行切割为体积占比60%与40%的两个部分。对占比60%的冰芯段的切割面，使用切片机进一步修整以获得新鲜平整的表面。在表面切割与修整完成后，即刻采用1MHz频率、1V的激励信号，将两个AC-ECM电极沿表面拖拽扫描。 本次测量覆盖了深度112.65米至2503.07米的全部冰芯，但2251.4米以下的测量数据质量不佳，因此本数据集仅公开至2251.4米深度。尽管信号采样间隔为2毫米，但为抑制噪声，我们仅绘制数据的10毫米滑动平均值。AC-ECM电极以约1厘米每秒的速度沿冰面手动拖拽。 AC-ECM系统由两个同轴电极与自动平衡电桥（惠普（HP）4284A型精密LCR表）构成。该系统通过1MHz频率测量冰面的复导纳Y = G + jB，其中G为电导，B为电纳，以获取冰的高频极限电导；此处的高频极限指频率仅高于德拜色散（Debye dispersion），且低于微波频段以上存在的色散效应。 电极与冰芯轴垂直对齐，间距为15毫米。根据电场强度与到给定电极的距离成反比的物理原理，电极的有效分辨率近似等于电极间距（15毫米）：在此间距内，约65%的电力线会穿过测量区域。 由于AC-ECM需要对自动平衡电桥、线缆与电极进行精准校准，我们采用三种参考材料——干燥空气、铝与特氟龙（Teflon）——对导纳测量结果进行校准。研究表明，校准不充分会使交流损耗因子的估算误差翻倍。 交流电导与硫酸及氢离子的浓度呈正比关系。所有测量数据均被转换为-25℃下的等效值。详细内容请参见Fujita等（2002）的研究。