Collaborative Research: Using Fracture Patterns and Ice Thickness to Study the History and Dynamics of Grounding Line Migration and Shutdown of Kamb and Whillans Ice Streams

该奖项支持一个为期三年的项目，该项目旨在开发解释罗斯冰架上复杂的流动特征模式所需的工具，该工具记录了从南极西部冰原向东流动的冰流的排放历史。这项工作建立在先前的研究基础上，该研究利用卫星图像拼接和冰架流动数值模型中可见的流动特征来检测数百年来地面区动力学的变化和冰流出口的重定向。最近观察到的惠兰斯冰流的变化符合这一框架。这种重定向模式是由快速的下游变薄对冰的基底热梯度和相关的“粘点”（冰升）形成的影响驱动的。在进行这项工作的过程中，研究人员发现了大陆架上其他的流量变化记录，这些记录可以用来建立一个更完整的冰流流量变化历史和理解。这项工作的智力价值在于，这些记录，包括裂缝模式和冰厚的空间变化，如果在适当的背景下被理解，将产生关于冰流减速的时间和动力学、接地线后退以及冰流之间的相对排放历史的定量信息。新的工具将有助于进一步限制这一历史。美国宇航局的IceSAT卫星上的激光高度计提高了我们对南极冰层表面高度的认识。IceSAT表面高程提供了冰架厚度的高分辨率地图，与冰架图像拼接的来源地图一起，将用于估计过去冰流排放事件（减速、重定向等）所涉及的冰量。本项目将开发新的裂缝扩展数值模型；这将使过去冰架应力状态的变化得以研究。动力学和体积通量的历史将为理解冰流流量的过去变化和潜在的物理过程提供一套强有力的观测资料。这个项目更广泛的影响集中在它如何有助于估计南极西部对全球海平面上升的贡献，以及回答有关千年冰流和更长期冰流演变的原因的悬而未决的问题。这项工作将提供已知最复杂的冰流记录的历史。除了将这项研究纳入研究生指导和正常教学职责之外，研究人员还参与了公民参与和教育的其他途径。这两个机构的调查人员每年都会向高中学生和广大社区宣传。波特兰州立大学的新推广项目是在具有学生学习和科学和数学成就方面专业知识的研究人员的协助下开发的。合作研究小组包括两名在高分辨率卫星图像和各种冰流模型配对方面有经验的冰川学家和一名专注于岩石变形力学的地质学家。

This award supports a three year project to develop the tools required to interpret complex patterns of flow features on the Ross Ice Shelf, which record the discharge history the ice streams flowing east off of the West Antarctic Ice Sheet. This work builds on previous research that used flow features visible in satellite image mosaics and numerical models of ice shelf flow to detect changes in grounding zone dynamics and redirection of ice stream outlets over hundreds of years. Recently observed changes on Whillans Ice Stream fit within this framework. The pattern of redirection is driven by the influence of rapid downstream thinning on the basal thermal gradient in the ice and associated "sticky spot" (ice rise) formation. In pursuing this work, the investigators recognized other records of discharge variation on the shelf that can be used to build a more complete history and understanding of ice-stream discharge variability. The intellectual merit of the proposed work lies in the fact that these records, including fracture patterns and spatial variation in ice thickness, when understood in the proper context, will yield quantitative information about the timing and dynamics of ice stream slowdowns, grounding line retreat, and the relative history of discharge between the ice streams. New tools will help further constrain this history. The laser altimeter on NASA's IceSAT has improved our knowledge of the surface elevation of Antarctic ice. IceSAT surface elevations provide a high-resolution map of ice-shelf thickness that, along with provenance maps from ice-shelf image mosaics, will be used to estimate the volumes of ice involved in past ice-stream discharge events (slowdowns, redirections, and so on). This project will develop new numerical models for fracture propagation; these will allow past variations in ice-shelf stress state to be investigated. Together, the dynamic and volume-flux histories will provide a powerful set of observations for understanding past variations in ice stream discharge and the underlying physical processes. The broader impacts of this project center on how it contributes to the ability to estimate West Antarctic contributions to global sea level rise and to answer outstanding questions about the causes of millennial and longer-scale evolution of ice streams. This work will provide a history of the most complex record of ice discharge known. In addition to the incorporation of this research into graduate student advising and normal teaching duties, the investigators are involved in other avenues of civic engagement and education. Outreach to high school students and the community at large is promoted on an annual basis by the investigators at both institutions. New outreach projects at Portland State University are developed with the assistance of researchers with expertise in student learning and achievement in science and mathematics. The collaborative research team includes two glaciologists with experience in the pairing of high resolution satellite imagery and a variety of ice-flow models and a geologist whose focus is the mechanics of rock deformation.