The effect of nanoparticles on the evolution of microstructure in polar ice (NEMI)

在南极和格陵兰的冰雪和冰川冰层中观察到的软冰与小颗粒和杂质的存在有关。一般认为，杂质通过钉扎晶界从而抑制其迁移来控制晶粒度。然而，杂质对这种影响的影响仍然存在很大的不确定性。关于不溶微粒和可溶离子的数据不完整地描绘了它们在冰中的存在以及它们在抑制晶界迁移方面的相关性。最近的数据显示，有明确的证据表明，钙离子浓度影响降雪和浅冰的致密化。没有理由认为这种相关性不适用于更深的冰层。然而，目前还不清楚这种影响是由钙直接引起的，还是它是其他某些杂质的替代品。理论强调了纳米颗粒的作用，但由于在冰中很难检测到这个颗粒大小范围，计算结果并未得到实验证据的支持。因此，为了了解纳米颗粒如何影响晶界迁移，我们将不同种类的纳米颗粒应用于多晶冰。我们专注于来自极地硅藻的抗冻蛋白(AFP)，已知这种颗粒可以抑制颗粒生长。我们认为这些蛋白质是冰中纳米颗粒的类似物。然而，考虑到北极和南极的深层冰中栖息着微生物，这些微生物可能通过风的运输到达中部地区，然后被包括在冰盖中，再考虑到AFP在极地地区广泛存在，可以想象南极和格陵兰的冰中确实存在蛋白质。除了AFP，钙和其他选定的纳米颗粒将被应用于实验。我们将主要使用冻结的多晶颗粒溶液，通过从冰I到冰II再回到冰I的相变方法，获得细粒度且没有变形的溶液。颗粒微观结构将由光学显微镜、拉曼光谱和自动织物分析仪确定。在第二步中，我们将分析掺入颗粒的雪，从而与自然条件相似。此外，为了了解粒子在边界迁移过程中的行为，无论它们是过度生长还是被迁移边界拖曳，我们将确定它们在冰中的局部化。在这最后一步中，荧光纳米粒子将在激光共聚焦显微镜下应用和观察，根据前几步获得的结果选择更有希望的实验条件。针对纳米粒子在影响多晶冰微结构中的作用，特别是AFP，该项目旨在通过跨学科的努力，填补冰芯分析和防冻剂研究方面的空白。

The soft ice observed in Antarctic and Greenland firn and glacial ice layers is related to small grain size and the presence of impurities. It is generally assumed that the impurities control the grain size by pinning grain boundaries and thus inhibiting their migration. However, large uncertainties persist on which impurities are responsible for this effect. Data on insoluble microparticles and soluble ions give an incomplete picture of their presence in ice and of their relevance in inhibiting grain boundary migration. Recent data show a clear evidence that calcium ion concentration affects densification in firn and shallow ice. There is no reason to assume that this correlation should not hold for deeper ice. However, it is unknown whether the effect is caused directly by calcium or if it is a proxy for some other impurity. Theory stresses the role of nanoparticles, but calculations are not supported by experimental evidence due to the fact that this particle size range is difficult to detect in ice. Therefore, in order to understand how nanoparticles affect grain boundary migration, we apply different kinds to polycrystalline ice. We focus on antifreeze proteins (AFPs) from polar diatoms, particles known to inhibit grain growth. We regard these proteins as analogues of nanoparticles within ice. However, considering that Arctic and Antarctic deep ice is populated by microorganisms, which may have reached the central regions by wind transport and then been included in the ice sheets, and considering that AFPs are widespread in the polar regions, it is conceivable that proteins are indeed present in Antarctic and Greenland ice. Besides AFPs, calcium and selected other nanoparticles will be applied to the experiments. We will work mainly with frozen polycrystalline particle solution, fine-grained and free of deformations through a phase-transition method from ice I to ice II and back to ice I. Grain boundaries will be observed in relation to time, temperature, particle type and concentration. Grain microstructure will be determined by optical microscopy, Raman spectroscopy and an Automated Fabric Analyzer. In a second step we will analyze snow doped with particles, thus resembling natural conditions. Furthermore, in order to understand how particles behave during boundary migration, whether they are overgrown or dragged along by the migrating boundaries, we will determine their localization in ice. In this last step fluorescent nanoparticles will be applied and observed at laser confocal microscopy, choosing the more promising experimental conditions based on the obtained results from previous steps.Addressing the role of nanoparticles in affecting the microstructure of polycrystalline ice with special emphasis on AFPs, this project aims to close, in an interdisciplinary effort, open gaps in both ice-core analysis and antifreeze research.