Interfacial Premelting and Geophysical Implications

该项目是对存在于冰晶边界的液态水在低于纯水冰点温度下的动力学进行为期三年的理论和实验研究的延续。这一过程被称为预融化，在海冰中盐水的重新分配、污染物通过冰川的明显迁移、土壤和岩石的冻胀和风化速率等方面具有重要影响。预熔对几乎所有类型的材料都是常见的，但对冰的研究最为广泛。它可以由吸附力、润湿、尺寸效应或衬底紊乱引起，并涉及表面物理和相变现象的许多方面。这些分子尺度过程的宏观结果包括季节冻结与海洋温盐环流之间的关系，以及古气候代理记录的定量解释。在更长的气候时间尺度上，南极冰芯揭示了最近冰期-间冰期旋回的总体特征，但破译驱动气候突变的机制需要更高的分辨率。从冰芯中获得的任何高分辨率古气候信息的准确性都必须依赖于对影响微量成分在冰原中长时间（100 kyr）停留时间的过程的适当处理。晶界融化被认为是控制物质通过排列在冰川冰粒交叉处的脉和结的预融化液体网络传输速率的主要过程。此外，晶界熔融的作用可以进一步增加液体含量，增强微量组分的迁移率。该项目有三个不同但相互关联的组成部分。在不同杂质存在的情况下，将直接测量晶界的预熔，作为温度和晶粒失配的函数，并对在剪切流存在的情况下，预测在不断增长的海冰/海洋界面上发生的不稳定性进行实验。两者都将辅以理论计算来证明实验问题，并在许多情况下追求预熔的影响。

This project is a three-year continuation of a theoretical and experimental study of the dynamics of liquid water existing at the boundaries of ice crystal at temperatures below the freezing point of pure water. This process, called premelting, has significant consequences in the redistributing of brine in sea ice, the apparent migrating of contaminants through glacier ice, and the rate of frost heave and weathering in soils and rocks. Premelting is common to virtually all types of materials, but has been most extensively studied in ice. It can be caused by adsorption forces, wetting, size effects, or substrate disorder, and involves many aspects of surface physics and phase transition phenomena. The macroscale consequences of these molecular-scale processes include the relationship between seasonal freezing and the oceanic thermohaline circulation, and the quantitative interpretations of paleoclimate proxy records. On the longer climatic time scales, the overall features of recent glacial-interglacial cycles have been revealed in the Antarctic ice cores, but higher resolution is required to decipher the mechanisms that drive abrupt climate changes. The accuracy of any higher resolution paleoclimatic information derived from ice cores will have to rely on the proper treatment of processes that affect the trace constituents during their long (100 kyr) residence times in the ice sheets. Grain-boundary melting is believed to be the primary process controlling the rate of material transport through the premelted-liquid networks of veins and nodes that line the grain intersections of glacier ice. Moreover, the role of grain-boundary melting can further increase the liquid content and enhance trace-constituent mobility.The project has three distinct, but interrelated components. Direct measurements of premelting of grain boundaries in the presence of different impurities will be made as a function of temperature and grain mismatch, and experiments on instabilities that are predicted to occur at the growing sea ice/ocean interface in the presence of a shear flow will be conducted. Both will be complemented by theoretical calculations to prove experimental issues and to pursue the implications of premelting in numerous contexts.