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: 1506307
• 负责人: Jason Amundson
• 金额: $ 9.68万
• 依托单位: University of Alaska Southeast Juneau Campus
• 依托单位国家: 美国
• 项目类别: Standard 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=1506307&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; jamming; iceberg

Non-Technical:This award is jointly funded by the Condensed Matter Physics Program and the Office of Multidisciplinary Affairs in MPS and the Artic Natural Sciences Program in GEO. 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 (10's to 100's 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MPS凝聚态物理项目和多学科事务办公室以及GEO北极自然科学项目联合资助。我们星球的极地地区是许多动态物理过程的所在地。尽管“冰川”一词可能会让人联想到坚忍不拔的冰山和缓慢移动的冰山，其变化肉眼无法区分，但情况并非总是如此。格陵兰岛广阔的沿海峡湾是冰川活动最活跃的地区之一。宽5-10公里、深达1公里的冰河正迅速流向海洋。在这些冰川的末端，即冰与大海的交汇处，冰山不断脱落或“崩解”到海洋中。排入海洋的所有冰中，大约有 30-50% 是通过崩解发生的，而不是融化等其他机制。不幸的是，控制产犊的物理过程尚不清楚。一种可能的影响是混冰的存在，它是由冰山和海冰组成的漂浮层，从冰川前端延伸数公里。混合物本质上是一种大规模的准二维颗粒材料，它可能对冰山崩解率和我们检测冰山崩解的能力产生重大影响。该合作项目旨在确定混冰力学的正确物理描述及其对冰山崩解的影响。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，该项目为塑造地球极地地区的潜在机制提供了新的线索。技术：该项目的主要目标是表征混冰的流变学特征，混冰是一种由冰山和海冰组成的紧密堆积的颗粒材料，存在于整个格陵兰岛的峡湾中。冰混合物在粒状材料中是独一无二的，因为它含有特别大的碎屑（各个方向的尺寸为数十米到数百米），被限制在准二维环境中流动，并漂浮在其自身的融化物中。混冰运动和范围的季节性变化与冰山崩解率的季节性变化密切相关，这表明混冰是对出口冰川和冰盖稳定性的重要控制因素。混合冰的动力学、能量学和海洋学后果基本上尚未被探索。研究小组的目标是通过将现场观察分析与实验室实验和数值模拟相结合来研究冰混合物。对卫星图像以及之前收集的延时摄影和地面雷达数据进行分析，以产生冰混合物速度场并量化冰山大小分布。这项工作提供了对混冰运动学和成分的新见解，并可作为实验室和数值模拟实验的基准。此外，还进行了由模型终点推动水箱中的人造冰山的实验。这些实验研究了模拟冰山在崩解事件期间和之间的粒子干扰，以研究通过混合冰的应力传递。最后，进行数值实验，其中使用改编自先前颗粒材料工作的离散粒子和连续体模型来模拟冰混合物。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。