Microparticles in a deep ice core drilled at NEEM, Greenland: cryogenic scanning electron microscopic observations of location, size, shape, and constituent elements

This report presents the analysis of microparticles contained in the deep ice core drilled at the North Greenland Eemian Ice Drilling (NEEM) site, using a cryogenic scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). By implementing additional optical microscopic analysis prior to cryogenic SEM/EDS analysis, it was possible to exclude microparticles formed during the cryogenic SEM/EDS experiments. The examined ice core samples were cut from depths corresponding to five different climate stages, from the Holocene period through the last interglacial epoch. Overall, 514 microparticles were observed via SEM, and 151 of those were also analyzed based on their EDS spectra to determine their chemical compositions. A catalog containing the details of all the observed microparticles was then constructed. The catalog presents optical and secondary electron images of microparticles, an area-equivalent diameter and aspect ratio of each microparticle, and its distance from the nearest grain boundary and air-inclusion (e.g., air bubble, hydrate, or plate-like inclusion). For microparticles analyzed with EDS, numerical data regarding the X-ray count, weight ratio, and atomic ratio are also included, and the atomic ratio is shown as a pie chart. In this report, we describe how the observations and analyses were carried out and how the catalog data were organized. The catalog is valuable for studies regarding the general paleoenvironment and the relationship between microparticles and the physical properties of ice-sheet ice.本报告针对北格陵兰埃姆冰芯钻探（North Greenland Eemian Ice Drilling, NEEM）位点获取的深冰芯所含微粒展开分析，实验采用配备能量色散X射线能谱仪（energy dispersive X-ray spectrometer, EDS）的低温扫描电子显微镜（cryogenic scanning electron microscope, SEM）。在开展低温SEM/EDS分析前，通过额外的光学显微分析（optical microscopic analysis），可排除低温实验过程中形成的微粒。本次分析的冰芯样品取自全新世（Holocene）至末次间冰期（last interglacial epoch）共5个不同气候阶段对应的深度。经扫描电子显微镜观测，共发现514个微粒，其中151个微粒借助EDS能谱完成了化学组成分析。随后构建了涵盖所有观测微粒详细信息的目录。该目录收录了微粒的光学图像与二次电子图像、各微粒的等效投影面积直径（area-equivalent diameter）与长径比（aspect ratio），以及其与最近晶粒边界（grain boundary）和空气包裹体（air-inclusion，如气泡、水合物或板状包裹体）之间的距离。对于经EDS分析的微粒，目录还包含X射线计数、重量占比与原子占比的数值数据，且原子占比以饼图形式呈现。本报告详述了本次观测与分析的实施流程，以及目录数据的组织方式。该目录对于开展综合古环境研究，以及探究微粒与冰盖冰物理性质之间的关联具有重要研究价值。