The microstructure of meteoric ice from Vostok, Antarctica
The microstructure of meteoric ice from Vostok, Antarctica
复制标题
南极洲沃斯托克流星冰的微观结构
作者：
R. Obbard;I. Baker
摘要 在南极洲东方站收集的 3623 米长的 5G 核心包含交替的流星冰层，具有两种截然不同的微观结构。在本文中，我们介绍了深度为 97 至 3416 m 的多个样本的微观结构和杂质含量，详细描述了不同层的特征，并提出了其微观结构发展的机制。使用数字图像分析、离子色谱、扫描电子显微镜和能量色散X射线光谱来测量纹理以及杂质的位置和类型；使用电子背散射衍射来确定晶体取向。与间冰期相关的冰的特征是相对较粗的晶粒和 c 轴在包含取芯方向的平面中的强烈择优取向，产生垂直腰围织物。相比之下，冰河时期的冰具有更小的颗粒尺寸和坚固的单最大结构，其中 c 轴聚集在垂直方向上。钙独特地存在于细粒冰川层的晶界中，其对晶界流动性的影响以及流动性的错误取向依赖性可以解释沃斯托克站冰川冰中所见的不连续微结构的发展。
Abstract The 3623 m long, 5G core collected at Vostok station, Antarctica, contains alternating layers of meteoric ice with two distinctly different microstructures. In this paper, we present the microstructure and impurity content of a number of specimens ranging in depth from 97 to 3416 m, describe in detail the characteristics of the different layers and propose a mechanism for their microstructural development. Digital image analysis, ion chromatography, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to measure texture and the location and type of impurities; electron backscatter diffraction was used to determine crystal orientation. The ice associated with interglacial periods is characterized by relatively coarse grains and a strong preferred orientation of the c axes in a plane encompassing the coring direction, producing a vertical-girdle fabric. In contrast, ice from glacial periods is characterized by a much smaller grain size and a strong singlemaximum fabric, where the c axes are clustered around the vertical. Calcium is uniquely present in the grain boundaries of the fine-grained glacial layers, and its effect on grain-boundary mobility and the misorientation dependence of mobility can explain the development of the discontinuous microstructure seen in glacial ice at Vostok station.