Interfacial Premelting and Geophysical Implications

该项目是对冰晶边界上存在的液态水在低于纯水冰点的温度下的动力学的理论和实验研究的三年的延续。这个被称为预融的过程对海冰中卤水的重新分配、污染物在冰川中的明显迁移以及土壤和岩石中的冻胀和风化速度具有重大影响。预融几乎对所有类型的材料都是常见的，但在冰中得到了最广泛的研究。它可能是由吸附力、润湿、尺寸效应或衬底无序引起的，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和海洋温盐环流之间的关系，以及对古气候替代记录的定量解释。在较长的气候时间尺度上，南极冰芯揭示了近期冰川-间冰期循环的总体特征，但需要更高的分辨率来破译驱动气候突变的机制。从冰芯获得的任何更高分辨率的古气候信息的准确性将取决于对影响痕量组分在冰盖中长时间(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冰川冰粒交汇处的纹理和节点的预融液体网络进行运输的主要过程。此外，晶界熔化的作用可以进一步增加液体含量和增强痕量组分的流动性。该项目有三个截然不同但相互关联的组成部分。将直接测量不同杂质存在下的晶界预熔，作为温度和颗粒失配的函数，并将对在剪切流存在时不断增长的海冰/海洋界面上预测发生的不稳定性进行实验。两者都将得到理论计算的补充，以证明实验问题，并在许多情况下探索预熔化的含义。

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.