Ice Core Colle Gnifetti KCC

We analysed crystal-preferred orientation of c-axis and microstructure data from the Alpine ice core KCC at an unprecedented resolution and coverage of any Alpine ice core. We find that an anisotropic single-maximum fabric develops as early as 25 m depth in firn under vertical compression and strengthens under simple shear conditions towards the bedrock at 72 m depth. The analysis of continuously measured intervals with subsequent thin section samples from several depths of the ice core reveals a high spatial variability in the crystal orientation and crystal size on the 10 cm-scale as well as within a few centimeters. We quantify the variability and investigate the possible causes and links to other microstructural properties. Our findings support the hypothesis that the observed variability is a consequence of strain localisation on small spatial scales with influence on fabric and microstructure. From a methodological perspective, the results of this study lead us to challenge whether single thin sections from ice cores provide representative parameters for their depth to be used to infer the fabric development in a glacier on the large scale. Previously proposed uncertainty estimates for fabric and grain size parameters do not capture the observed variability. This might therefore demand a new scale-sensitive statistical approach.

本研究针对阿尔卑斯冰芯KCC的c轴晶体优选取向（crystal-preferred orientation）与微观结构数据展开分析，其分辨率与覆盖范围达到了阿尔卑斯冰芯研究中的前所未有的水准。研究发现，在垂直压缩作用下的粒雪（firn）中，各向异性单极大组构最早可在25米深度处形成，并在72米深度朝向基岩的简单剪切环境中逐步强化。通过对连续测量段及冰芯多个深度的后续薄片样品开展分析，结果显示晶体取向与晶体粒径在10厘米尺度乃至数厘米范围内均存在显著的空间异质性。本研究对该异质性进行了定量表征，并探讨了其潜在成因以及与其他微观结构属性的关联。研究结果支持下述假说：观测到的空间异质性源于小尺度空间范围内的应变局域化，该过程会对晶体组构与微观结构产生影响。从方法学视角来看，本研究的结果促使我们重新审视：冰芯的单一切片样品能否为其所在深度提供具有代表性的参数，以用于推断大尺度冰川的晶体组构演化过程。此前针对组构与粒径参数提出的不确定性估计方法未能覆盖本次观测到的异质性，因此这一现状或亟需提出新的尺度敏感统计方法。