基于微粒变化对崇测冰帽浅层冰芯的定年结果

Dating of a Shallow Ice Core from Chongce Ice Cap Using Micro-particle Content

冰芯年代学的建立, 对于稳定同位素定年方法失效的钻点尤为困难. 依据粒径在0.66～1.33μm之间的不可溶尘埃微粒的浓度垂向分布, 并结合阳离子Ca2+的浓度剖面变化, 实现了对崇测冰帽冰芯浅层的断代. 该冰芯钻自海拔6 532 m的冰穹顶部, 解析的18.7 m冰芯长度占到钻点冰层深度约2/5, 辅助的定年参数包括钻点表层5 a的实测净积累率和大气核试验的地层标志. 综合各种技巧定年, 崇测冰帽该冰芯覆盖的记录年代为1902-1992年, 最底部累积误差在±2 a(约为2%).

An accurate time scale is necessary for interpretation of an ice core record. The establishment of chronology is especially difficult for sites where the conventional annual--layer counting using stable isotopes fails due to much less snow deposition. In this work, dating from the analysis of insoluble micro-particles ranging from 0. 66 to 1.33μm in diameter, in combination with the soluble Ca^2＋ concentration, was applied to an ice core from a middle-sized Chongce Ice Cap, West Kunlun Mountains of China. The ice core was retrieved from the summit, 6 530 ma. s. 1., of the ice cap. The dated core of 18. 7 m in length represents about 2/5 of the total ice thickness at the drilling site. The assisting dating parameters include the measured net accumulation in the last 5 years prior to the drilling and the stratigraphic marker of atmospheric nuclear weapon test. Based on the combined techniques, a time scale covering the period of 1903--1992 was derived. The cumulative dating uncertainty by the bottom is estimated less than 2 years. This work suggests that the insoluble microparticle takes an advantage in the dating of ice cores from Asian mountainous glaciers. The concentration in a certain size range （〈2 μm）, rather than the total concentration, is more preferable. It is significant to exclude the possible “noise”of weathered mineral dust of local sources.