Collaborative Research: Investigating jamming in iceberg-choked fjords with field observations, laboratory experiments, and numerical models

合作研究：通过现场观察、实验室实验和数值模型研究冰山堵塞的峡湾中的干扰

• 批准号: 1506446
• 负责人: Justin Burton
• 金额: $ 25.64万
• 依托单位: Emory University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506446&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; jamming; iceberg

Nontechnical:This award is jointly funded by the Condensed Matter Physics Program and the Office of Multidisciplinary Activities in Math and Physical Sciences and the Artic Natural Sciences Program in Geosciences. The polar regions of our planet are home to many dynamic physical processes. Although the word "glacier" may invoke connotations of stoic and slow-moving mountains of ice whose changes are indistinguishable to the eye, this is not always the case. Among the most active regions of glaciological activity are the massive coastal fjords in Greenland. Rivers of ice which are 5-10 km wide and up to 1 km deep are rapidly flowing towards the ocean. At the end of these glaciers, where the ice meets the sea, icebergs are constantly breaking off or "calving" into the ocean. Approximately 30-50% of all ice discharged into the ocean occurs through calving, as opposed to other mechanisms such as melting. Unfortunately, the physical processes which control calving are not well understood. One possible influence is the presence of an ice mélange, which is a floating layer of icebergs and sea ice extending many kilometers away from the front of the glacier. The mélange is essentially a large-scale, quasi-two dimensional granular material, which can potentially have a large impact on calving rates and our ability to detect iceberg calving. This collaborative project aims to determine the correct physical description of ice mélange mechanics, as well as its influences on iceberg calving. This is accomplished through an interdisciplinary combination of satellite imagery, small-scale laboratory experiments, and theoretical modeling. By bringing together ideas in condensed matter physics to study large-scale glaciological processes, the project sheds new light on the underlying mechanisms which shape the polar regions of our planet. Technical:The primary goal of this project is to characterize the rheology of ice mélange, a closely-packed granular material composed of icebergs and sea ice that is found in fjords throughout Greenland. Ice mélange is unique among granular materials in that it contains exceptionally large clasts (10s to 100s of meters in scale in all directions), is constrained to flow in a quasi-two-dimensional setting, and floats in its own melt. Seasonal variations in ice mélange motion and extent are well-correlated with seasonal variations in iceberg calving rates, suggesting that ice mélange is an important control on outlet glacier and ice sheet stability. The dynamics, energetics, and oceanographic consequences of ice mélange are essentially unexplored. The research team's aim is to study ice mélange by combining analysis of field observations with laboratory experiments and numerical modeling. Satellite imagery, along with previously collected time lapse photography and terrestrial radar data, is analyzed to produce ice mélange velocity fields and quantify iceberg-size distributions. This work provides new insights into ice mélange kinematics and composition, and serves as a benchmark for laboratory and numerical modeling experiments. In addition, experiments are conducted in which synthetic icebergs in a water tank are pushed by a model terminus. These experiments study jamming of particles that model icebergs during and between calving events to investigate stress transmission through ice mélange. Finally, numerical experiments are performed in which ice mélange is simulated using discrete particle and continuum models adapted from previous work on granular materials. The model rheology can be adjusted to find a description of ice mélange that is consistent with field observations and laboratory experiments.

非技术性：该奖项由凝聚态物理计划和数学与物理科学多学科活动办公室以及地球科学中的北极自然科学计划共同资助。地球的极地地区是许多动态物理过程的所在地。虽然“冰川”这个词可能会让人联想到坚忍和缓慢移动的冰山，它们的变化肉眼难以分辨，但情况并非总是如此。冰川活动最活跃的地区之一是格陵兰岛巨大的沿海峡湾。5-10公里宽、1公里深的冰河正迅速流向海洋。在这些冰川的末端，在冰与海相遇的地方，冰山不断地断裂或“崩解”到海洋中。大约30-50%的冰排放到海洋中是通过产裂作用发生的，而不是其他机制，如融化。不幸的是，控制产犊的物理过程还没有得到很好的理解。一个可能的影响是冰混合物的存在，这是一个漂浮的冰山和海冰层，从冰川前部延伸出许多公里。混合物本质上是一种大规模的准二维颗粒状物质，可能会对产犊率和我们检测冰山产犊的能力产生巨大影响。这个合作项目的目的是确定正确的物理描述冰混合力学，以及它对冰山崩解的影响。这是通过卫星图像，小规模实验室实验和理论建模的跨学科组合来实现的。通过汇集凝聚态物理学的思想来研究大规模的冰川过程，该项目揭示了塑造我们星球极地地区的潜在机制。技术：该项目的主要目标是描述冰混合物的流变学特征，冰混合物是一种由冰山和海冰组成的紧密堆积的颗粒状材料，在格陵兰岛的峡湾中发现。冰溷合物在颗粒物质中是独一无二的，因为它包含非常大的碎屑（各个方向的尺度为10到100米），被限制在准二维环境中流动，并漂浮在自己的熔体中。冰混合运动和范围的季节变化与冰山崩解率的季节变化密切相关，表明冰混合是出口冰川和冰盖稳定性的重要控制因素。冰混杂的动力学、能量学和海洋学后果基本上是未被探索的。该研究小组的目标是通过将实地观测分析与实验室实验和数值模拟相结合来研究冰混合。卫星图像，沿着与以前收集的时间推移摄影和地面雷达数据，进行分析，以产生冰混合速度场和量化冰山的大小分布。这项工作提供了新的见解冰混杂运动学和组成，并作为实验室和数值模拟实验的基准。此外，还进行了由模型末端推动水箱中的合成冰山的实验。这些实验研究了在崩解事件期间和之间对模拟冰山的颗粒的干扰，以研究通过冰混合物的应力传递。最后，数值实验中，冰混合模拟离散颗粒和连续体模型改编自以前的工作颗粒状材料。可以调整模型流变学，以找到与现场观察和实验室实验一致的冰混合物的描述。